Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 8408 insertions, 0 deletions

diff --git a/third_party/rust/hashbrown/src/map.rs b/third_party/rust/hashbrown/src/map.rs
new file mode 100644
index 0000000000..a5d3ccb97e
--- /dev/null
+++ b/third_party/rust/hashbrown/src/map.rs
@@ -0,0 +1,8408 @@
+use crate::raw::{Allocator, Bucket, Global, RawDrain, RawIntoIter, RawIter, RawTable};
+use crate::TryReserveError;
+use core::borrow::Borrow;
+use core::fmt::{self, Debug};
+use core::hash::{BuildHasher, Hash};
+use core::iter::{FromIterator, FusedIterator};
+use core::marker::PhantomData;
+use core::mem;
+use core::ops::Index;
+
+/// Default hasher for `HashMap`.
+#[cfg(feature = "ahash")]
+pub type DefaultHashBuilder = ahash::RandomState;
+
+/// Dummy default hasher for `HashMap`.
+#[cfg(not(feature = "ahash"))]
+pub enum DefaultHashBuilder {}
+
+/// A hash map implemented with quadratic probing and SIMD lookup.
+///
+/// The default hashing algorithm is currently [`AHash`], though this is
+/// subject to change at any point in the future. This hash function is very
+/// fast for all types of keys, but this algorithm will typically *not* protect
+/// against attacks such as HashDoS.
+///
+/// The hashing algorithm can be replaced on a per-`HashMap` basis using the
+/// [`default`], [`with_hasher`], and [`with_capacity_and_hasher`] methods. Many
+/// alternative algorithms are available on crates.io, such as the [`fnv`] crate.
+///
+/// It is required that the keys implement the [`Eq`] and [`Hash`] traits, although
+/// this can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`.
+/// If you implement these yourself, it is important that the following
+/// property holds:
+///
+/// ```text
+/// k1 == k2 -> hash(k1) == hash(k2)
+/// ```
+///
+/// In other words, if two keys are equal, their hashes must be equal.
+///
+/// It is a logic error for a key to be modified in such a way that the key's
+/// hash, as determined by the [`Hash`] trait, or its equality, as determined by
+/// the [`Eq`] trait, changes while it is in the map. This is normally only
+/// possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
+///
+/// It is also a logic error for the [`Hash`] implementation of a key to panic.
+/// This is generally only possible if the trait is implemented manually. If a
+/// panic does occur then the contents of the `HashMap` may become corrupted and
+/// some items may be dropped from the table.
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// // Type inference lets us omit an explicit type signature (which
+/// // would be `HashMap<String, String>` in this example).
+/// let mut book_reviews = HashMap::new();
+///
+/// // Review some books.
+/// book_reviews.insert(
+///     "Adventures of Huckleberry Finn".to_string(),
+///     "My favorite book.".to_string(),
+/// );
+/// book_reviews.insert(
+///     "Grimms' Fairy Tales".to_string(),
+///     "Masterpiece.".to_string(),
+/// );
+/// book_reviews.insert(
+///     "Pride and Prejudice".to_string(),
+///     "Very enjoyable.".to_string(),
+/// );
+/// book_reviews.insert(
+///     "The Adventures of Sherlock Holmes".to_string(),
+///     "Eye lyked it alot.".to_string(),
+/// );
+///
+/// // Check for a specific one.
+/// // When collections store owned values (String), they can still be
+/// // queried using references (&str).
+/// if !book_reviews.contains_key("Les Misérables") {
+///     println!("We've got {} reviews, but Les Misérables ain't one.",
+///              book_reviews.len());
+/// }
+///
+/// // oops, this review has a lot of spelling mistakes, let's delete it.
+/// book_reviews.remove("The Adventures of Sherlock Holmes");
+///
+/// // Look up the values associated with some keys.
+/// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
+/// for &book in &to_find {
+///     match book_reviews.get(book) {
+///         Some(review) => println!("{}: {}", book, review),
+///         None => println!("{} is unreviewed.", book)
+///     }
+/// }
+///
+/// // Look up the value for a key (will panic if the key is not found).
+/// println!("Review for Jane: {}", book_reviews["Pride and Prejudice"]);
+///
+/// // Iterate over everything.
+/// for (book, review) in &book_reviews {
+///     println!("{}: \"{}\"", book, review);
+/// }
+/// ```
+///
+/// `HashMap` also implements an [`Entry API`](#method.entry), which allows
+/// for more complex methods of getting, setting, updating and removing keys and
+/// their values:
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// // type inference lets us omit an explicit type signature (which
+/// // would be `HashMap<&str, u8>` in this example).
+/// let mut player_stats = HashMap::new();
+///
+/// fn random_stat_buff() -> u8 {
+///     // could actually return some random value here - let's just return
+///     // some fixed value for now
+///     42
+/// }
+///
+/// // insert a key only if it doesn't already exist
+/// player_stats.entry("health").or_insert(100);
+///
+/// // insert a key using a function that provides a new value only if it
+/// // doesn't already exist
+/// player_stats.entry("defence").or_insert_with(random_stat_buff);
+///
+/// // update a key, guarding against the key possibly not being set
+/// let stat = player_stats.entry("attack").or_insert(100);
+/// *stat += random_stat_buff();
+/// ```
+///
+/// The easiest way to use `HashMap` with a custom key type is to derive [`Eq`] and [`Hash`].
+/// We must also derive [`PartialEq`].
+///
+/// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+/// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+/// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
+/// [`RefCell`]: https://doc.rust-lang.org/std/cell/struct.RefCell.html
+/// [`Cell`]: https://doc.rust-lang.org/std/cell/struct.Cell.html
+/// [`default`]: #method.default
+/// [`with_hasher`]: #method.with_hasher
+/// [`with_capacity_and_hasher`]: #method.with_capacity_and_hasher
+/// [`fnv`]: https://crates.io/crates/fnv
+/// [`AHash`]: https://crates.io/crates/ahash
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// #[derive(Hash, Eq, PartialEq, Debug)]
+/// struct Viking {
+///     name: String,
+///     country: String,
+/// }
+///
+/// impl Viking {
+///     /// Creates a new Viking.
+///     fn new(name: &str, country: &str) -> Viking {
+///         Viking { name: name.to_string(), country: country.to_string() }
+///     }
+/// }
+///
+/// // Use a HashMap to store the vikings' health points.
+/// let mut vikings = HashMap::new();
+///
+/// vikings.insert(Viking::new("Einar", "Norway"), 25);
+/// vikings.insert(Viking::new("Olaf", "Denmark"), 24);
+/// vikings.insert(Viking::new("Harald", "Iceland"), 12);
+///
+/// // Use derived implementation to print the status of the vikings.
+/// for (viking, health) in &vikings {
+///     println!("{:?} has {} hp", viking, health);
+/// }
+/// ```
+///
+/// A `HashMap` with fixed list of elements can be initialized from an array:
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let timber_resources: HashMap<&str, i32> = [("Norway", 100), ("Denmark", 50), ("Iceland", 10)]
+///     .iter().cloned().collect();
+/// // use the values stored in map
+/// ```
+pub struct HashMap<K, V, S = DefaultHashBuilder, A: Allocator + Clone = Global> {
+    pub(crate) hash_builder: S,
+    pub(crate) table: RawTable<(K, V), A>,
+}
+
+impl<K: Clone, V: Clone, S: Clone, A: Allocator + Clone> Clone for HashMap<K, V, S, A> {
+    fn clone(&self) -> Self {
+        HashMap {
+            hash_builder: self.hash_builder.clone(),
+            table: self.table.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, source: &Self) {
+        self.table.clone_from(&source.table);
+
+        // Update hash_builder only if we successfully cloned all elements.
+        self.hash_builder.clone_from(&source.hash_builder);
+    }
+}
+
+/// Ensures that a single closure type across uses of this which, in turn prevents multiple
+/// instances of any functions like RawTable::reserve from being generated
+#[cfg_attr(feature = "inline-more", inline)]
+pub(crate) fn make_hasher<K, Q, V, S>(hash_builder: &S) -> impl Fn(&(Q, V)) -> u64 + '_
+where
+    K: Borrow<Q>,
+    Q: Hash,
+    S: BuildHasher,
+{
+    move |val| make_hash::<K, Q, S>(hash_builder, &val.0)
+}
+
+/// Ensures that a single closure type across uses of this which, in turn prevents multiple
+/// instances of any functions like RawTable::reserve from being generated
+#[cfg_attr(feature = "inline-more", inline)]
+fn equivalent_key<Q, K, V>(k: &Q) -> impl Fn(&(K, V)) -> bool + '_
+where
+    K: Borrow<Q>,
+    Q: ?Sized + Eq,
+{
+    move |x| k.eq(x.0.borrow())
+}
+
+/// Ensures that a single closure type across uses of this which, in turn prevents multiple
+/// instances of any functions like RawTable::reserve from being generated
+#[cfg_attr(feature = "inline-more", inline)]
+fn equivalent<Q, K>(k: &Q) -> impl Fn(&K) -> bool + '_
+where
+    K: Borrow<Q>,
+    Q: ?Sized + Eq,
+{
+    move |x| k.eq(x.borrow())
+}
+
+#[cfg(not(feature = "nightly"))]
+#[cfg_attr(feature = "inline-more", inline)]
+pub(crate) fn make_hash<K, Q, S>(hash_builder: &S, val: &Q) -> u64
+where
+    K: Borrow<Q>,
+    Q: Hash + ?Sized,
+    S: BuildHasher,
+{
+    use core::hash::Hasher;
+    let mut state = hash_builder.build_hasher();
+    val.hash(&mut state);
+    state.finish()
+}
+
+#[cfg(feature = "nightly")]
+#[cfg_attr(feature = "inline-more", inline)]
+pub(crate) fn make_hash<K, Q, S>(hash_builder: &S, val: &Q) -> u64
+where
+    K: Borrow<Q>,
+    Q: Hash + ?Sized,
+    S: BuildHasher,
+{
+    hash_builder.hash_one(val)
+}
+
+#[cfg(not(feature = "nightly"))]
+#[cfg_attr(feature = "inline-more", inline)]
+pub(crate) fn make_insert_hash<K, S>(hash_builder: &S, val: &K) -> u64
+where
+    K: Hash,
+    S: BuildHasher,
+{
+    use core::hash::Hasher;
+    let mut state = hash_builder.build_hasher();
+    val.hash(&mut state);
+    state.finish()
+}
+
+#[cfg(feature = "nightly")]
+#[cfg_attr(feature = "inline-more", inline)]
+pub(crate) fn make_insert_hash<K, S>(hash_builder: &S, val: &K) -> u64
+where
+    K: Hash,
+    S: BuildHasher,
+{
+    hash_builder.hash_one(val)
+}
+
+#[cfg(feature = "ahash")]
+impl<K, V> HashMap<K, V, DefaultHashBuilder> {
+    /// Creates an empty `HashMap`.
+    ///
+    /// The hash map is initially created with a capacity of 0, so it will not allocate until it
+    /// is first inserted into.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// let mut map: HashMap<&str, i32> = HashMap::new();
+    /// assert_eq!(map.len(), 0);
+    /// assert_eq!(map.capacity(), 0);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Creates an empty `HashMap` with the specified capacity.
+    ///
+    /// The hash map will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash map will not allocate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
+    /// assert_eq!(map.len(), 0);
+    /// assert!(map.capacity() >= 10);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self::with_capacity_and_hasher(capacity, DefaultHashBuilder::default())
+    }
+}
+
+#[cfg(feature = "ahash")]
+impl<K, V, A: Allocator + Clone> HashMap<K, V, DefaultHashBuilder, A> {
+    /// Creates an empty `HashMap` using the given allocator.
+    ///
+    /// The hash map is initially created with a capacity of 0, so it will not allocate until it
+    /// is first inserted into.
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn new_in(alloc: A) -> Self {
+        Self::with_hasher_in(DefaultHashBuilder::default(), alloc)
+    }
+
+    /// Creates an empty `HashMap` with the specified capacity using the given allocator.
+    ///
+    /// The hash map will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash map will not allocate.
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
+        Self::with_capacity_and_hasher_in(capacity, DefaultHashBuilder::default(), alloc)
+    }
+}
+
+impl<K, V, S> HashMap<K, V, S> {
+    /// Creates an empty `HashMap` which will use the given hash builder to hash
+    /// keys.
+    ///
+    /// The hash map is initially created with a capacity of 0, so it will not
+    /// allocate until it is first inserted into.
+    ///
+    /// Warning: `hash_builder` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the HashMap to be useful, see its documentation for details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut map = HashMap::with_hasher(s);
+    /// assert_eq!(map.len(), 0);
+    /// assert_eq!(map.capacity(), 0);
+    ///
+    /// map.insert(1, 2);
+    /// ```
+    ///
+    /// [`BuildHasher`]: https://doc.rust-lang.org/std/hash/trait.BuildHasher.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub const fn with_hasher(hash_builder: S) -> Self {
+        Self {
+            hash_builder,
+            table: RawTable::new(),
+        }
+    }
+
+    /// Creates an empty `HashMap` with the specified capacity, using `hash_builder`
+    /// to hash the keys.
+    ///
+    /// The hash map will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash map will not allocate.
+    ///
+    /// Warning: `hash_builder` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
+    /// the HashMap to be useful, see its documentation for details.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut map = HashMap::with_capacity_and_hasher(10, s);
+    /// assert_eq!(map.len(), 0);
+    /// assert!(map.capacity() >= 10);
+    ///
+    /// map.insert(1, 2);
+    /// ```
+    ///
+    /// [`BuildHasher`]: https://doc.rust-lang.org/std/hash/trait.BuildHasher.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self {
+        Self {
+            hash_builder,
+            table: RawTable::with_capacity(capacity),
+        }
+    }
+}
+
+impl<K, V, S, A: Allocator + Clone> HashMap<K, V, S, A> {
+    /// Returns a reference to the underlying allocator.
+    #[inline]
+    pub fn allocator(&self) -> &A {
+        self.table.allocator()
+    }
+
+    /// Creates an empty `HashMap` which will use the given hash builder to hash
+    /// keys. It will be allocated with the given allocator.
+    ///
+    /// The created map has the default initial capacity.
+    ///
+    /// Warning: `hash_builder` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut map = HashMap::with_hasher(s);
+    /// map.insert(1, 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_hasher_in(hash_builder: S, alloc: A) -> Self {
+        Self {
+            hash_builder,
+            table: RawTable::new_in(alloc),
+        }
+    }
+
+    /// Creates an empty `HashMap` with the specified capacity, using `hash_builder`
+    /// to hash the keys. It will be allocated with the given allocator.
+    ///
+    /// The hash map will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash map will not allocate.
+    ///
+    /// Warning: `hash_builder` is normally randomly generated, and
+    /// is designed to allow HashMaps to be resistant to attacks that
+    /// cause many collisions and very poor performance. Setting it
+    /// manually using this function can expose a DoS attack vector.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut map = HashMap::with_capacity_and_hasher(10, s);
+    /// map.insert(1, 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity_and_hasher_in(capacity: usize, hash_builder: S, alloc: A) -> Self {
+        Self {
+            hash_builder,
+            table: RawTable::with_capacity_in(capacity, alloc),
+        }
+    }
+
+    /// Returns a reference to the map's [`BuildHasher`].
+    ///
+    /// [`BuildHasher`]: https://doc.rust-lang.org/std/hash/trait.BuildHasher.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let hasher = DefaultHashBuilder::default();
+    /// let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
+    /// let hasher: &DefaultHashBuilder = map.hasher();
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn hasher(&self) -> &S {
+        &self.hash_builder
+    }
+
+    /// Returns the number of elements the map can hold without reallocating.
+    ///
+    /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
+    /// more, but is guaranteed to be able to hold at least this many.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// let map: HashMap<i32, i32> = HashMap::with_capacity(100);
+    /// assert_eq!(map.len(), 0);
+    /// assert!(map.capacity() >= 100);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn capacity(&self) -> usize {
+        self.table.capacity()
+    }
+
+    /// An iterator visiting all keys in arbitrary order.
+    /// The iterator element type is `&'a K`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    /// assert_eq!(map.len(), 3);
+    /// let mut vec: Vec<&str> = Vec::new();
+    ///
+    /// for key in map.keys() {
+    ///     println!("{}", key);
+    ///     vec.push(*key);
+    /// }
+    ///
+    /// // The `Keys` iterator produces keys in arbitrary order, so the
+    /// // keys must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, ["a", "b", "c"]);
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn keys(&self) -> Keys<'_, K, V> {
+        Keys { inner: self.iter() }
+    }
+
+    /// An iterator visiting all values in arbitrary order.
+    /// The iterator element type is `&'a V`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    /// assert_eq!(map.len(), 3);
+    /// let mut vec: Vec<i32> = Vec::new();
+    ///
+    /// for val in map.values() {
+    ///     println!("{}", val);
+    ///     vec.push(*val);
+    /// }
+    ///
+    /// // The `Values` iterator produces values in arbitrary order, so the
+    /// // values must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [1, 2, 3]);
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn values(&self) -> Values<'_, K, V> {
+        Values { inner: self.iter() }
+    }
+
+    /// An iterator visiting all values mutably in arbitrary order.
+    /// The iterator element type is `&'a mut V`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    ///
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// for val in map.values_mut() {
+    ///     *val = *val + 10;
+    /// }
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// let mut vec: Vec<i32> = Vec::new();
+    ///
+    /// for val in map.values() {
+    ///     println!("{}", val);
+    ///     vec.push(*val);
+    /// }
+    ///
+    /// // The `Values` iterator produces values in arbitrary order, so the
+    /// // values must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [11, 12, 13]);
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
+        ValuesMut {
+            inner: self.iter_mut(),
+        }
+    }
+
+    /// An iterator visiting all key-value pairs in arbitrary order.
+    /// The iterator element type is `(&'a K, &'a V)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    /// assert_eq!(map.len(), 3);
+    /// let mut vec: Vec<(&str, i32)> = Vec::new();
+    ///
+    /// for (key, val) in map.iter() {
+    ///     println!("key: {} val: {}", key, val);
+    ///     vec.push((*key, *val));
+    /// }
+    ///
+    /// // The `Iter` iterator produces items in arbitrary order, so the
+    /// // items must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3)]);
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn iter(&self) -> Iter<'_, K, V> {
+        // Here we tie the lifetime of self to the iter.
+        unsafe {
+            Iter {
+                inner: self.table.iter(),
+                marker: PhantomData,
+            }
+        }
+    }
+
+    /// An iterator visiting all key-value pairs in arbitrary order,
+    /// with mutable references to the values.
+    /// The iterator element type is `(&'a K, &'a mut V)`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// // Update all values
+    /// for (_, val) in map.iter_mut() {
+    ///     *val *= 2;
+    /// }
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// let mut vec: Vec<(&str, i32)> = Vec::new();
+    ///
+    /// for (key, val) in &map {
+    ///     println!("key: {} val: {}", key, val);
+    ///     vec.push((*key, *val));
+    /// }
+    ///
+    /// // The `Iter` iterator produces items in arbitrary order, so the
+    /// // items must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [("a", 2), ("b", 4), ("c", 6)]);
+    ///
+    /// assert_eq!(map.len(), 3);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
+        // Here we tie the lifetime of self to the iter.
+        unsafe {
+            IterMut {
+                inner: self.table.iter(),
+                marker: PhantomData,
+            }
+        }
+    }
+
+    #[cfg(test)]
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn raw_capacity(&self) -> usize {
+        self.table.buckets()
+    }
+
+    /// Returns the number of elements in the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// assert_eq!(a.len(), 0);
+    /// a.insert(1, "a");
+    /// assert_eq!(a.len(), 1);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn len(&self) -> usize {
+        self.table.len()
+    }
+
+    /// Returns `true` if the map contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// assert!(a.is_empty());
+    /// a.insert(1, "a");
+    /// assert!(!a.is_empty());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Clears the map, returning all key-value pairs as an iterator. Keeps the
+    /// allocated memory for reuse.
+    ///
+    /// If the returned iterator is dropped before being fully consumed, it
+    /// drops the remaining key-value pairs. The returned iterator keeps a
+    /// mutable borrow on the vector to optimize its implementation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// a.insert(1, "a");
+    /// a.insert(2, "b");
+    /// let capacity_before_drain = a.capacity();
+    ///
+    /// for (k, v) in a.drain().take(1) {
+    ///     assert!(k == 1 || k == 2);
+    ///     assert!(v == "a" || v == "b");
+    /// }
+    ///
+    /// // As we can see, the map is empty and contains no element.
+    /// assert!(a.is_empty() && a.len() == 0);
+    /// // But map capacity is equal to old one.
+    /// assert_eq!(a.capacity(), capacity_before_drain);
+    ///
+    /// let mut a = HashMap::new();
+    /// a.insert(1, "a");
+    /// a.insert(2, "b");
+    ///
+    /// {   // Iterator is dropped without being consumed.
+    ///     let d = a.drain();
+    /// }
+    ///
+    /// // But the map is empty even if we do not use Drain iterator.
+    /// assert!(a.is_empty());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn drain(&mut self) -> Drain<'_, K, V, A> {
+        Drain {
+            inner: self.table.drain(),
+        }
+    }
+
+    /// Retains only the elements specified by the predicate. Keeps the
+    /// allocated memory for reuse.
+    ///
+    /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)` returns `false`.
+    /// The elements are visited in unsorted (and unspecified) order.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
+    /// assert_eq!(map.len(), 8);
+    /// let capacity_before_retain = map.capacity();
+    ///
+    /// map.retain(|&k, _| k % 2 == 0);
+    ///
+    /// // We can see, that the number of elements inside map is changed.
+    /// assert_eq!(map.len(), 4);
+    /// // But map capacity is equal to old one.
+    /// assert_eq!(map.capacity(), capacity_before_retain);
+    ///
+    /// let mut vec: Vec<(i32, i32)> = map.iter().map(|(&k, &v)| (k, v)).collect();
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [(0, 0), (2, 20), (4, 40), (6, 60)]);
+    /// ```
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        // Here we only use `iter` as a temporary, preventing use-after-free
+        unsafe {
+            for item in self.table.iter() {
+                let &mut (ref key, ref mut value) = item.as_mut();
+                if !f(key, value) {
+                    self.table.erase(item);
+                }
+            }
+        }
+    }
+
+    /// Drains elements which are true under the given predicate,
+    /// and returns an iterator over the removed items.
+    ///
+    /// In other words, move all pairs `(k, v)` such that `f(&k, &mut v)` returns `true` out
+    /// into another iterator.
+    ///
+    /// Note that `drain_filter` lets you mutate every value in the filter closure, regardless of
+    /// whether you choose to keep or remove it.
+    ///
+    /// When the returned DrainedFilter is dropped, any remaining elements that satisfy
+    /// the predicate are dropped from the table.
+    ///
+    /// It is unspecified how many more elements will be subjected to the closure
+    /// if a panic occurs in the closure, or a panic occurs while dropping an element,
+    /// or if the `DrainFilter` value is leaked.
+    ///
+    /// Keeps the allocated memory for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
+    /// let capacity_before_drain_filter = map.capacity();
+    /// let drained: HashMap<i32, i32> = map.drain_filter(|k, _v| k % 2 == 0).collect();
+    ///
+    /// let mut evens = drained.keys().cloned().collect::<Vec<_>>();
+    /// let mut odds = map.keys().cloned().collect::<Vec<_>>();
+    /// evens.sort();
+    /// odds.sort();
+    ///
+    /// assert_eq!(evens, vec![0, 2, 4, 6]);
+    /// assert_eq!(odds, vec![1, 3, 5, 7]);
+    /// // Map capacity is equal to old one.
+    /// assert_eq!(map.capacity(), capacity_before_drain_filter);
+    ///
+    /// let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();
+    ///
+    /// {   // Iterator is dropped without being consumed.
+    ///     let d = map.drain_filter(|k, _v| k % 2 != 0);
+    /// }
+    ///
+    /// // But the map lens have been reduced by half
+    /// // even if we do not use DrainFilter iterator.
+    /// assert_eq!(map.len(), 4);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn drain_filter<F>(&mut self, f: F) -> DrainFilter<'_, K, V, F, A>
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        DrainFilter {
+            f,
+            inner: DrainFilterInner {
+                iter: unsafe { self.table.iter() },
+                table: &mut self.table,
+            },
+        }
+    }
+
+    /// Clears the map, removing all key-value pairs. Keeps the allocated memory
+    /// for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut a = HashMap::new();
+    /// a.insert(1, "a");
+    /// let capacity_before_clear = a.capacity();
+    ///
+    /// a.clear();
+    ///
+    /// // Map is empty.
+    /// assert!(a.is_empty());
+    /// // But map capacity is equal to old one.
+    /// assert_eq!(a.capacity(), capacity_before_clear);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn clear(&mut self) {
+        self.table.clear();
+    }
+
+    /// Creates a consuming iterator visiting all the keys in arbitrary order.
+    /// The map cannot be used after calling this.
+    /// The iterator element type is `K`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// let mut vec: Vec<&str> = map.into_keys().collect();
+    ///
+    /// // The `IntoKeys` iterator produces keys in arbitrary order, so the
+    /// // keys must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, ["a", "b", "c"]);
+    /// ```
+    #[inline]
+    pub fn into_keys(self) -> IntoKeys<K, V, A> {
+        IntoKeys {
+            inner: self.into_iter(),
+        }
+    }
+
+    /// Creates a consuming iterator visiting all the values in arbitrary order.
+    /// The map cannot be used after calling this.
+    /// The iterator element type is `V`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert("a", 1);
+    /// map.insert("b", 2);
+    /// map.insert("c", 3);
+    ///
+    /// let mut vec: Vec<i32> = map.into_values().collect();
+    ///
+    /// // The `IntoValues` iterator produces values in arbitrary order, so
+    /// // the values must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [1, 2, 3]);
+    /// ```
+    #[inline]
+    pub fn into_values(self) -> IntoValues<K, V, A> {
+        IntoValues {
+            inner: self.into_iter(),
+        }
+    }
+}
+
+impl<K, V, S, A> HashMap<K, V, S, A>
+where
+    K: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    /// Reserves capacity for at least `additional` more elements to be inserted
+    /// in the `HashMap`. The collection may reserve more space to avoid
+    /// frequent reallocations.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new allocation size overflows [`usize`].
+    ///
+    /// [`usize`]: https://doc.rust-lang.org/std/primitive.usize.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// let mut map: HashMap<&str, i32> = HashMap::new();
+    /// // Map is empty and doesn't allocate memory
+    /// assert_eq!(map.capacity(), 0);
+    ///
+    /// map.reserve(10);
+    ///
+    /// // And now map can hold at least 10 elements
+    /// assert!(map.capacity() >= 10);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn reserve(&mut self, additional: usize) {
+        self.table
+            .reserve(additional, make_hasher::<K, _, V, S>(&self.hash_builder));
+    }
+
+    /// Tries to reserve capacity for at least `additional` more elements to be inserted
+    /// in the given `HashMap<K,V>`. The collection may reserve more space to avoid
+    /// frequent reallocations.
+    ///
+    /// # Errors
+    ///
+    /// If the capacity overflows, or the allocator reports a failure, then an error
+    /// is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, isize> = HashMap::new();
+    /// // Map is empty and doesn't allocate memory
+    /// assert_eq!(map.capacity(), 0);
+    ///
+    /// map.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");
+    ///
+    /// // And now map can hold at least 10 elements
+    /// assert!(map.capacity() >= 10);
+    /// ```
+    /// If the capacity overflows, or the allocator reports a failure, then an error
+    /// is returned:
+    /// ```
+    /// # fn test() {
+    /// use hashbrown::HashMap;
+    /// use hashbrown::TryReserveError;
+    /// let mut map: HashMap<i32, i32> = HashMap::new();
+    ///
+    /// match map.try_reserve(usize::MAX) {
+    ///     Err(error) => match error {
+    ///         TryReserveError::CapacityOverflow => {}
+    ///         _ => panic!("TryReserveError::AllocError ?"),
+    ///     },
+    ///     _ => panic!(),
+    /// }
+    /// # }
+    /// # fn main() {
+    /// #     #[cfg(not(miri))]
+    /// #     test()
+    /// # }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
+        self.table
+            .try_reserve(additional, make_hasher::<K, _, V, S>(&self.hash_builder))
+    }
+
+    /// Shrinks the capacity of the map as much as possible. It will drop
+    /// down as much as possible while maintaining the internal rules
+    /// and possibly leaving some space in accordance with the resize policy.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
+    /// map.insert(1, 2);
+    /// map.insert(3, 4);
+    /// assert!(map.capacity() >= 100);
+    /// map.shrink_to_fit();
+    /// assert!(map.capacity() >= 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn shrink_to_fit(&mut self) {
+        self.table
+            .shrink_to(0, make_hasher::<K, _, V, S>(&self.hash_builder));
+    }
+
+    /// Shrinks the capacity of the map with a lower limit. It will drop
+    /// down no lower than the supplied limit while maintaining the internal rules
+    /// and possibly leaving some space in accordance with the resize policy.
+    ///
+    /// This function does nothing if the current capacity is smaller than the
+    /// supplied minimum capacity.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
+    /// map.insert(1, 2);
+    /// map.insert(3, 4);
+    /// assert!(map.capacity() >= 100);
+    /// map.shrink_to(10);
+    /// assert!(map.capacity() >= 10);
+    /// map.shrink_to(0);
+    /// assert!(map.capacity() >= 2);
+    /// map.shrink_to(10);
+    /// assert!(map.capacity() >= 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn shrink_to(&mut self, min_capacity: usize) {
+        self.table
+            .shrink_to(min_capacity, make_hasher::<K, _, V, S>(&self.hash_builder));
+    }
+
+    /// Gets the given key's corresponding entry in the map for in-place manipulation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut letters = HashMap::new();
+    ///
+    /// for ch in "a short treatise on fungi".chars() {
+    ///     let counter = letters.entry(ch).or_insert(0);
+    ///     *counter += 1;
+    /// }
+    ///
+    /// assert_eq!(letters[&'s'], 2);
+    /// assert_eq!(letters[&'t'], 3);
+    /// assert_eq!(letters[&'u'], 1);
+    /// assert_eq!(letters.get(&'y'), None);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn entry(&mut self, key: K) -> Entry<'_, K, V, S, A> {
+        let hash = make_insert_hash::<K, S>(&self.hash_builder, &key);
+        if let Some(elem) = self.table.find(hash, equivalent_key(&key)) {
+            Entry::Occupied(OccupiedEntry {
+                hash,
+                key: Some(key),
+                elem,
+                table: self,
+            })
+        } else {
+            Entry::Vacant(VacantEntry {
+                hash,
+                key,
+                table: self,
+            })
+        }
+    }
+
+    /// Gets the given key's corresponding entry by reference in the map for in-place manipulation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut words: HashMap<String, usize> = HashMap::new();
+    /// let source = ["poneyland", "horseyland", "poneyland", "poneyland"];
+    /// for (i, &s) in source.iter().enumerate() {
+    ///     let counter = words.entry_ref(s).or_insert(0);
+    ///     *counter += 1;
+    /// }
+    ///
+    /// assert_eq!(words["poneyland"], 3);
+    /// assert_eq!(words["horseyland"], 1);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn entry_ref<'a, 'b, Q: ?Sized>(&'a mut self, key: &'b Q) -> EntryRef<'a, 'b, K, Q, V, S, A>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        let hash = make_hash::<K, Q, S>(&self.hash_builder, key);
+        if let Some(elem) = self.table.find(hash, equivalent_key(key)) {
+            EntryRef::Occupied(OccupiedEntryRef {
+                hash,
+                key: Some(KeyOrRef::Borrowed(key)),
+                elem,
+                table: self,
+            })
+        } else {
+            EntryRef::Vacant(VacantEntryRef {
+                hash,
+                key: KeyOrRef::Borrowed(key),
+                table: self,
+            })
+        }
+    }
+
+    /// Returns a reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// assert_eq!(map.get(&1), Some(&"a"));
+    /// assert_eq!(map.get(&2), None);
+    /// ```
+    #[inline]
+    pub fn get<Q: ?Sized>(&self, k: &Q) -> Option<&V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.get_inner(k) {
+            Some(&(_, ref v)) => Some(v),
+            None => None,
+        }
+    }
+
+    /// Returns the key-value pair corresponding to the supplied key.
+    ///
+    /// The supplied key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
+    /// assert_eq!(map.get_key_value(&2), None);
+    /// ```
+    #[inline]
+    pub fn get_key_value<Q: ?Sized>(&self, k: &Q) -> Option<(&K, &V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.get_inner(k) {
+            Some(&(ref key, ref value)) => Some((key, value)),
+            None => None,
+        }
+    }
+
+    #[inline]
+    fn get_inner<Q: ?Sized>(&self, k: &Q) -> Option<&(K, V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        if self.table.is_empty() {
+            None
+        } else {
+            let hash = make_hash::<K, Q, S>(&self.hash_builder, k);
+            self.table.get(hash, equivalent_key(k))
+        }
+    }
+
+    /// Returns the key-value pair corresponding to the supplied key, with a mutable reference to value.
+    ///
+    /// The supplied key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// let (k, v) = map.get_key_value_mut(&1).unwrap();
+    /// assert_eq!(k, &1);
+    /// assert_eq!(v, &mut "a");
+    /// *v = "b";
+    /// assert_eq!(map.get_key_value_mut(&1), Some((&1, &mut "b")));
+    /// assert_eq!(map.get_key_value_mut(&2), None);
+    /// ```
+    #[inline]
+    pub fn get_key_value_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<(&K, &mut V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.get_inner_mut(k) {
+            Some(&mut (ref key, ref mut value)) => Some((key, value)),
+            None => None,
+        }
+    }
+
+    /// Returns `true` if the map contains a value for the specified key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// assert_eq!(map.contains_key(&1), true);
+    /// assert_eq!(map.contains_key(&2), false);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.get_inner(k).is_some()
+    }
+
+    /// Returns a mutable reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, "a");
+    /// if let Some(x) = map.get_mut(&1) {
+    ///     *x = "b";
+    /// }
+    /// assert_eq!(map[&1], "b");
+    ///
+    /// assert_eq!(map.get_mut(&2), None);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.get_inner_mut(k) {
+            Some(&mut (_, ref mut v)) => Some(v),
+            None => None,
+        }
+    }
+
+    #[inline]
+    fn get_inner_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut (K, V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        if self.table.is_empty() {
+            None
+        } else {
+            let hash = make_hash::<K, Q, S>(&self.hash_builder, k);
+            self.table.get_mut(hash, equivalent_key(k))
+        }
+    }
+
+    /// Attempts to get mutable references to `N` values in the map at once.
+    ///
+    /// Returns an array of length `N` with the results of each query. For soundness, at most one
+    /// mutable reference will be returned to any value. `None` will be returned if any of the
+    /// keys are duplicates or missing.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut libraries = HashMap::new();
+    /// libraries.insert("Bodleian Library".to_string(), 1602);
+    /// libraries.insert("Athenæum".to_string(), 1807);
+    /// libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
+    /// libraries.insert("Library of Congress".to_string(), 1800);
+    ///
+    /// let got = libraries.get_many_mut([
+    ///     "Athenæum",
+    ///     "Library of Congress",
+    /// ]);
+    /// assert_eq!(
+    ///     got,
+    ///     Some([
+    ///         &mut 1807,
+    ///         &mut 1800,
+    ///     ]),
+    /// );
+    ///
+    /// // Missing keys result in None
+    /// let got = libraries.get_many_mut([
+    ///     "Athenæum",
+    ///     "New York Public Library",
+    /// ]);
+    /// assert_eq!(got, None);
+    ///
+    /// // Duplicate keys result in None
+    /// let got = libraries.get_many_mut([
+    ///     "Athenæum",
+    ///     "Athenæum",
+    /// ]);
+    /// assert_eq!(got, None);
+    /// ```
+    pub fn get_many_mut<Q: ?Sized, const N: usize>(&mut self, ks: [&Q; N]) -> Option<[&'_ mut V; N]>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.get_many_mut_inner(ks).map(|res| res.map(|(_, v)| v))
+    }
+
+    /// Attempts to get mutable references to `N` values in the map at once, without validating that
+    /// the values are unique.
+    ///
+    /// Returns an array of length `N` with the results of each query. `None` will be returned if
+    /// any of the keys are missing.
+    ///
+    /// For a safe alternative see [`get_many_mut`](`HashMap::get_many_mut`).
+    ///
+    /// # Safety
+    ///
+    /// Calling this method with overlapping keys is *[undefined behavior]* even if the resulting
+    /// references are not used.
+    ///
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut libraries = HashMap::new();
+    /// libraries.insert("Bodleian Library".to_string(), 1602);
+    /// libraries.insert("Athenæum".to_string(), 1807);
+    /// libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
+    /// libraries.insert("Library of Congress".to_string(), 1800);
+    ///
+    /// let got = libraries.get_many_mut([
+    ///     "Athenæum",
+    ///     "Library of Congress",
+    /// ]);
+    /// assert_eq!(
+    ///     got,
+    ///     Some([
+    ///         &mut 1807,
+    ///         &mut 1800,
+    ///     ]),
+    /// );
+    ///
+    /// // Missing keys result in None
+    /// let got = libraries.get_many_mut([
+    ///     "Athenæum",
+    ///     "New York Public Library",
+    /// ]);
+    /// assert_eq!(got, None);
+    /// ```
+    pub unsafe fn get_many_unchecked_mut<Q: ?Sized, const N: usize>(
+        &mut self,
+        ks: [&Q; N],
+    ) -> Option<[&'_ mut V; N]>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.get_many_unchecked_mut_inner(ks)
+            .map(|res| res.map(|(_, v)| v))
+    }
+
+    /// Attempts to get mutable references to `N` values in the map at once, with immutable
+    /// references to the corresponding keys.
+    ///
+    /// Returns an array of length `N` with the results of each query. For soundness, at most one
+    /// mutable reference will be returned to any value. `None` will be returned if any of the keys
+    /// are duplicates or missing.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut libraries = HashMap::new();
+    /// libraries.insert("Bodleian Library".to_string(), 1602);
+    /// libraries.insert("Athenæum".to_string(), 1807);
+    /// libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
+    /// libraries.insert("Library of Congress".to_string(), 1800);
+    ///
+    /// let got = libraries.get_many_key_value_mut([
+    ///     "Bodleian Library",
+    ///     "Herzogin-Anna-Amalia-Bibliothek",
+    /// ]);
+    /// assert_eq!(
+    ///     got,
+    ///     Some([
+    ///         (&"Bodleian Library".to_string(), &mut 1602),
+    ///         (&"Herzogin-Anna-Amalia-Bibliothek".to_string(), &mut 1691),
+    ///     ]),
+    /// );
+    /// // Missing keys result in None
+    /// let got = libraries.get_many_key_value_mut([
+    ///     "Bodleian Library",
+    ///     "Gewandhaus",
+    /// ]);
+    /// assert_eq!(got, None);
+    ///
+    /// // Duplicate keys result in None
+    /// let got = libraries.get_many_key_value_mut([
+    ///     "Bodleian Library",
+    ///     "Herzogin-Anna-Amalia-Bibliothek",
+    ///     "Herzogin-Anna-Amalia-Bibliothek",
+    /// ]);
+    /// assert_eq!(got, None);
+    /// ```
+    pub fn get_many_key_value_mut<Q: ?Sized, const N: usize>(
+        &mut self,
+        ks: [&Q; N],
+    ) -> Option<[(&'_ K, &'_ mut V); N]>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.get_many_mut_inner(ks)
+            .map(|res| res.map(|(k, v)| (&*k, v)))
+    }
+
+    /// Attempts to get mutable references to `N` values in the map at once, with immutable
+    /// references to the corresponding keys, without validating that the values are unique.
+    ///
+    /// Returns an array of length `N` with the results of each query. `None` will be returned if
+    /// any of the keys are missing.
+    ///
+    /// For a safe alternative see [`get_many_key_value_mut`](`HashMap::get_many_key_value_mut`).
+    ///
+    /// # Safety
+    ///
+    /// Calling this method with overlapping keys is *[undefined behavior]* even if the resulting
+    /// references are not used.
+    ///
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut libraries = HashMap::new();
+    /// libraries.insert("Bodleian Library".to_string(), 1602);
+    /// libraries.insert("Athenæum".to_string(), 1807);
+    /// libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
+    /// libraries.insert("Library of Congress".to_string(), 1800);
+    ///
+    /// let got = libraries.get_many_key_value_mut([
+    ///     "Bodleian Library",
+    ///     "Herzogin-Anna-Amalia-Bibliothek",
+    /// ]);
+    /// assert_eq!(
+    ///     got,
+    ///     Some([
+    ///         (&"Bodleian Library".to_string(), &mut 1602),
+    ///         (&"Herzogin-Anna-Amalia-Bibliothek".to_string(), &mut 1691),
+    ///     ]),
+    /// );
+    /// // Missing keys result in None
+    /// let got = libraries.get_many_key_value_mut([
+    ///     "Bodleian Library",
+    ///     "Gewandhaus",
+    /// ]);
+    /// assert_eq!(got, None);
+    /// ```
+    pub unsafe fn get_many_key_value_unchecked_mut<Q: ?Sized, const N: usize>(
+        &mut self,
+        ks: [&Q; N],
+    ) -> Option<[(&'_ K, &'_ mut V); N]>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.get_many_unchecked_mut_inner(ks)
+            .map(|res| res.map(|(k, v)| (&*k, v)))
+    }
+
+    fn get_many_mut_inner<Q: ?Sized, const N: usize>(
+        &mut self,
+        ks: [&Q; N],
+    ) -> Option<[&'_ mut (K, V); N]>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        let hashes = self.build_hashes_inner(ks);
+        self.table
+            .get_many_mut(hashes, |i, (k, _)| ks[i].eq(k.borrow()))
+    }
+
+    unsafe fn get_many_unchecked_mut_inner<Q: ?Sized, const N: usize>(
+        &mut self,
+        ks: [&Q; N],
+    ) -> Option<[&'_ mut (K, V); N]>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        let hashes = self.build_hashes_inner(ks);
+        self.table
+            .get_many_unchecked_mut(hashes, |i, (k, _)| ks[i].eq(k.borrow()))
+    }
+
+    fn build_hashes_inner<Q: ?Sized, const N: usize>(&self, ks: [&Q; N]) -> [u64; N]
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        let mut hashes = [0_u64; N];
+        for i in 0..N {
+            hashes[i] = make_hash::<K, Q, S>(&self.hash_builder, ks[i]);
+        }
+        hashes
+    }
+
+    /// Inserts a key-value pair into the map.
+    ///
+    /// If the map did not have this key present, [`None`] is returned.
+    ///
+    /// If the map did have this key present, the value is updated, and the old
+    /// value is returned. The key is not updated, though; this matters for
+    /// types that can be `==` without being identical. See the [`std::collections`]
+    /// [module-level documentation] for more.
+    ///
+    /// [`None`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
+    /// [`std::collections`]: https://doc.rust-lang.org/std/collections/index.html
+    /// [module-level documentation]: https://doc.rust-lang.org/std/collections/index.html#insert-and-complex-keys
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// assert_eq!(map.insert(37, "a"), None);
+    /// assert_eq!(map.is_empty(), false);
+    ///
+    /// map.insert(37, "b");
+    /// assert_eq!(map.insert(37, "c"), Some("b"));
+    /// assert_eq!(map[&37], "c");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(&mut self, k: K, v: V) -> Option<V> {
+        let hash = make_insert_hash::<K, S>(&self.hash_builder, &k);
+        if let Some((_, item)) = self.table.get_mut(hash, equivalent_key(&k)) {
+            Some(mem::replace(item, v))
+        } else {
+            self.table
+                .insert(hash, (k, v), make_hasher::<K, _, V, S>(&self.hash_builder));
+            None
+        }
+    }
+
+    /// Insert a key-value pair into the map without checking
+    /// if the key already exists in the map.
+    ///
+    /// Returns a reference to the key and value just inserted.
+    ///
+    /// This operation is safe if a key does not exist in the map.
+    ///
+    /// However, if a key exists in the map already, the behavior is unspecified:
+    /// this operation may panic, loop forever, or any following operation with the map
+    /// may panic, loop forever or return arbitrary result.
+    ///
+    /// That said, this operation (and following operations) are guaranteed to
+    /// not violate memory safety.
+    ///
+    /// This operation is faster than regular insert, because it does not perform
+    /// lookup before insertion.
+    ///
+    /// This operation is useful during initial population of the map.
+    /// For example, when constructing a map from another map, we know
+    /// that keys are unique.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map1 = HashMap::new();
+    /// assert_eq!(map1.insert(1, "a"), None);
+    /// assert_eq!(map1.insert(2, "b"), None);
+    /// assert_eq!(map1.insert(3, "c"), None);
+    /// assert_eq!(map1.len(), 3);
+    ///
+    /// let mut map2 = HashMap::new();
+    ///
+    /// for (key, value) in map1.into_iter() {
+    ///     map2.insert_unique_unchecked(key, value);
+    /// }
+    ///
+    /// let (key, value) = map2.insert_unique_unchecked(4, "d");
+    /// assert_eq!(key, &4);
+    /// assert_eq!(value, &mut "d");
+    /// *value = "e";
+    ///
+    /// assert_eq!(map2[&1], "a");
+    /// assert_eq!(map2[&2], "b");
+    /// assert_eq!(map2[&3], "c");
+    /// assert_eq!(map2[&4], "e");
+    /// assert_eq!(map2.len(), 4);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert_unique_unchecked(&mut self, k: K, v: V) -> (&K, &mut V) {
+        let hash = make_insert_hash::<K, S>(&self.hash_builder, &k);
+        let bucket = self
+            .table
+            .insert(hash, (k, v), make_hasher::<K, _, V, S>(&self.hash_builder));
+        let (k_ref, v_ref) = unsafe { bucket.as_mut() };
+        (k_ref, v_ref)
+    }
+
+    /// Tries to insert a key-value pair into the map, and returns
+    /// a mutable reference to the value in the entry.
+    ///
+    /// # Errors
+    ///
+    /// If the map already had this key present, nothing is updated, and
+    /// an error containing the occupied entry and the value is returned.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::OccupiedError;
+    ///
+    /// let mut map = HashMap::new();
+    /// assert_eq!(map.try_insert(37, "a").unwrap(), &"a");
+    ///
+    /// match map.try_insert(37, "b") {
+    ///     Err(OccupiedError { entry, value }) => {
+    ///         assert_eq!(entry.key(), &37);
+    ///         assert_eq!(entry.get(), &"a");
+    ///         assert_eq!(value, "b");
+    ///     }
+    ///     _ => panic!()
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn try_insert(
+        &mut self,
+        key: K,
+        value: V,
+    ) -> Result<&mut V, OccupiedError<'_, K, V, S, A>> {
+        match self.entry(key) {
+            Entry::Occupied(entry) => Err(OccupiedError { entry, value }),
+            Entry::Vacant(entry) => Ok(entry.insert(value)),
+        }
+    }
+
+    /// Removes a key from the map, returning the value at the key if the key
+    /// was previously in the map. Keeps the allocated memory for reuse.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// // The map is empty
+    /// assert!(map.is_empty() && map.capacity() == 0);
+    ///
+    /// map.insert(1, "a");
+    /// let capacity_before_remove = map.capacity();
+    ///
+    /// assert_eq!(map.remove(&1), Some("a"));
+    /// assert_eq!(map.remove(&1), None);
+    ///
+    /// // Now map holds none elements but capacity is equal to the old one
+    /// assert!(map.len() == 0 && map.capacity() == capacity_before_remove);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.remove_entry(k) {
+            Some((_, v)) => Some(v),
+            None => None,
+        }
+    }
+
+    /// Removes a key from the map, returning the stored key and value if the
+    /// key was previously in the map. Keeps the allocated memory for reuse.
+    ///
+    /// The key may be any borrowed form of the map's key type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the key type.
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// // The map is empty
+    /// assert!(map.is_empty() && map.capacity() == 0);
+    ///
+    /// map.insert(1, "a");
+    /// let capacity_before_remove = map.capacity();
+    ///
+    /// assert_eq!(map.remove_entry(&1), Some((1, "a")));
+    /// assert_eq!(map.remove(&1), None);
+    ///
+    /// // Now map hold none elements but capacity is equal to the old one
+    /// assert!(map.len() == 0 && map.capacity() == capacity_before_remove);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)>
+    where
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        let hash = make_hash::<K, Q, S>(&self.hash_builder, k);
+        self.table.remove_entry(hash, equivalent_key(k))
+    }
+}
+
+impl<K, V, S, A: Allocator + Clone> HashMap<K, V, S, A> {
+    /// Creates a raw entry builder for the HashMap.
+    ///
+    /// Raw entries provide the lowest level of control for searching and
+    /// manipulating a map. They must be manually initialized with a hash and
+    /// then manually searched. After this, insertions into a vacant entry
+    /// still require an owned key to be provided.
+    ///
+    /// Raw entries are useful for such exotic situations as:
+    ///
+    /// * Hash memoization
+    /// * Deferring the creation of an owned key until it is known to be required
+    /// * Using a search key that doesn't work with the Borrow trait
+    /// * Using custom comparison logic without newtype wrappers
+    ///
+    /// Because raw entries provide much more low-level control, it's much easier
+    /// to put the HashMap into an inconsistent state which, while memory-safe,
+    /// will cause the map to produce seemingly random results. Higher-level and
+    /// more foolproof APIs like `entry` should be preferred when possible.
+    ///
+    /// In particular, the hash used to initialized the raw entry must still be
+    /// consistent with the hash of the key that is ultimately stored in the entry.
+    /// This is because implementations of HashMap may need to recompute hashes
+    /// when resizing, at which point only the keys are available.
+    ///
+    /// Raw entries give mutable access to the keys. This must not be used
+    /// to modify how the key would compare or hash, as the map will not re-evaluate
+    /// where the key should go, meaning the keys may become "lost" if their
+    /// location does not reflect their state. For instance, if you change a key
+    /// so that the map now contains keys which compare equal, search may start
+    /// acting erratically, with two keys randomly masking each other. Implementations
+    /// are free to assume this doesn't happen (within the limits of memory-safety).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map = HashMap::new();
+    /// map.extend([("a", 100), ("b", 200), ("c", 300)]);
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// // Existing key (insert and update)
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => unreachable!(),
+    ///     RawEntryMut::Occupied(mut view) => {
+    ///         assert_eq!(view.get(), &100);
+    ///         let v = view.get_mut();
+    ///         let new_v = (*v) * 10;
+    ///         *v = new_v;
+    ///         assert_eq!(view.insert(1111), 1000);
+    ///     }
+    /// }
+    ///
+    /// assert_eq!(map[&"a"], 1111);
+    /// assert_eq!(map.len(), 3);
+    ///
+    /// // Existing key (take)
+    /// let hash = compute_hash(map.hasher(), &"c");
+    /// match map.raw_entry_mut().from_key_hashed_nocheck(hash, &"c") {
+    ///     RawEntryMut::Vacant(_) => unreachable!(),
+    ///     RawEntryMut::Occupied(view) => {
+    ///         assert_eq!(view.remove_entry(), ("c", 300));
+    ///     }
+    /// }
+    /// assert_eq!(map.raw_entry().from_key(&"c"), None);
+    /// assert_eq!(map.len(), 2);
+    ///
+    /// // Nonexistent key (insert and update)
+    /// let key = "d";
+    /// let hash = compute_hash(map.hasher(), &key);
+    /// match map.raw_entry_mut().from_hash(hash, |q| *q == key) {
+    ///     RawEntryMut::Occupied(_) => unreachable!(),
+    ///     RawEntryMut::Vacant(view) => {
+    ///         let (k, value) = view.insert("d", 4000);
+    ///         assert_eq!((*k, *value), ("d", 4000));
+    ///         *value = 40000;
+    ///     }
+    /// }
+    /// assert_eq!(map[&"d"], 40000);
+    /// assert_eq!(map.len(), 3);
+    ///
+    /// match map.raw_entry_mut().from_hash(hash, |q| *q == key) {
+    ///     RawEntryMut::Vacant(_) => unreachable!(),
+    ///     RawEntryMut::Occupied(view) => {
+    ///         assert_eq!(view.remove_entry(), ("d", 40000));
+    ///     }
+    /// }
+    /// assert_eq!(map.get(&"d"), None);
+    /// assert_eq!(map.len(), 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<'_, K, V, S, A> {
+        RawEntryBuilderMut { map: self }
+    }
+
+    /// Creates a raw immutable entry builder for the HashMap.
+    ///
+    /// Raw entries provide the lowest level of control for searching and
+    /// manipulating a map. They must be manually initialized with a hash and
+    /// then manually searched.
+    ///
+    /// This is useful for
+    /// * Hash memoization
+    /// * Using a search key that doesn't work with the Borrow trait
+    /// * Using custom comparison logic without newtype wrappers
+    ///
+    /// Unless you are in such a situation, higher-level and more foolproof APIs like
+    /// `get` should be preferred.
+    ///
+    /// Immutable raw entries have very limited use; you might instead want `raw_entry_mut`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.extend([("a", 100), ("b", 200), ("c", 300)]);
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// for k in ["a", "b", "c", "d", "e", "f"] {
+    ///     let hash = compute_hash(map.hasher(), k);
+    ///     let v = map.get(&k).cloned();
+    ///     let kv = v.as_ref().map(|v| (&k, v));
+    ///
+    ///     println!("Key: {} and value: {:?}", k, v);
+    ///
+    ///     assert_eq!(map.raw_entry().from_key(&k), kv);
+    ///     assert_eq!(map.raw_entry().from_hash(hash, |q| *q == k), kv);
+    ///     assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash, &k), kv);
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn raw_entry(&self) -> RawEntryBuilder<'_, K, V, S, A> {
+        RawEntryBuilder { map: self }
+    }
+
+    /// Returns a mutable reference to the [`RawTable`] used underneath [`HashMap`].
+    /// This function is only available if the `raw` feature of the crate is enabled.
+    ///
+    /// # Note
+    ///
+    /// Calling the function safe, but using raw hash table API's may require
+    /// unsafe functions or blocks.
+    ///
+    /// `RawTable` API gives the lowest level of control under the map that can be useful
+    /// for extending the HashMap's API, but may lead to *[undefined behavior]*.
+    ///
+    /// [`HashMap`]: struct.HashMap.html
+    /// [`RawTable`]: raw/struct.RawTable.html
+    /// [undefined behavior]: https://doc.rust-lang.org/reference/behavior-considered-undefined.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.extend([("a", 10), ("b", 20), ("c", 30)]);
+    /// assert_eq!(map.len(), 3);
+    ///
+    /// // Let's imagine that we have a value and a hash of the key, but not the key itself.
+    /// // However, if you want to remove the value from the map by hash and value, and you
+    /// // know exactly that the value is unique, then you can create a function like this:
+    /// fn remove_by_hash<K, V, S, F>(
+    ///     map: &mut HashMap<K, V, S>,
+    ///     hash: u64,
+    ///     is_match: F,
+    /// ) -> Option<(K, V)>
+    /// where
+    ///     F: Fn(&(K, V)) -> bool,
+    /// {
+    ///     let raw_table = map.raw_table();
+    ///     match raw_table.find(hash, is_match) {
+    ///         Some(bucket) => Some(unsafe { raw_table.remove(bucket) }),
+    ///         None => None,
+    ///     }
+    /// }
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// let hash = compute_hash(map.hasher(), "a");
+    /// assert_eq!(remove_by_hash(&mut map, hash, |(_, v)| *v == 10), Some(("a", 10)));
+    /// assert_eq!(map.get(&"a"), None);
+    /// assert_eq!(map.len(), 2);
+    /// ```
+    #[cfg(feature = "raw")]
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn raw_table(&mut self) -> &mut RawTable<(K, V), A> {
+        &mut self.table
+    }
+}
+
+impl<K, V, S, A> PartialEq for HashMap<K, V, S, A>
+where
+    K: Eq + Hash,
+    V: PartialEq,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    fn eq(&self, other: &Self) -> bool {
+        if self.len() != other.len() {
+            return false;
+        }
+
+        self.iter()
+            .all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
+    }
+}
+
+impl<K, V, S, A> Eq for HashMap<K, V, S, A>
+where
+    K: Eq + Hash,
+    V: Eq,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+}
+
+impl<K, V, S, A> Debug for HashMap<K, V, S, A>
+where
+    K: Debug,
+    V: Debug,
+    A: Allocator + Clone,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_map().entries(self.iter()).finish()
+    }
+}
+
+impl<K, V, S, A> Default for HashMap<K, V, S, A>
+where
+    S: Default,
+    A: Default + Allocator + Clone,
+{
+    /// Creates an empty `HashMap<K, V, S, A>`, with the `Default` value for the hasher and allocator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use std::collections::hash_map::RandomState;
+    ///
+    /// // You can specify all types of HashMap, including hasher and allocator.
+    /// // Created map is empty and don't allocate memory
+    /// let map: HashMap<u32, String> = Default::default();
+    /// assert_eq!(map.capacity(), 0);
+    /// let map: HashMap<u32, String, RandomState> = HashMap::default();
+    /// assert_eq!(map.capacity(), 0);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn default() -> Self {
+        Self::with_hasher_in(Default::default(), Default::default())
+    }
+}
+
+impl<K, Q: ?Sized, V, S, A> Index<&Q> for HashMap<K, V, S, A>
+where
+    K: Eq + Hash + Borrow<Q>,
+    Q: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    type Output = V;
+
+    /// Returns a reference to the value corresponding to the supplied key.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the key is not present in the `HashMap`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let map: HashMap<_, _> = [("a", "One"), ("b", "Two")].into();
+    ///
+    /// assert_eq!(map[&"a"], "One");
+    /// assert_eq!(map[&"b"], "Two");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn index(&self, key: &Q) -> &V {
+        self.get(key).expect("no entry found for key")
+    }
+}
+
+// The default hasher is used to match the std implementation signature
+#[cfg(feature = "ahash")]
+impl<K, V, A, const N: usize> From<[(K, V); N]> for HashMap<K, V, DefaultHashBuilder, A>
+where
+    K: Eq + Hash,
+    A: Default + Allocator + Clone,
+{
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let map1 = HashMap::from([(1, 2), (3, 4)]);
+    /// let map2: HashMap<_, _> = [(1, 2), (3, 4)].into();
+    /// assert_eq!(map1, map2);
+    /// ```
+    fn from(arr: [(K, V); N]) -> Self {
+        arr.into_iter().collect()
+    }
+}
+
+/// An iterator over the entries of a `HashMap` in arbitrary order.
+/// The iterator element type is `(&'a K, &'a V)`.
+///
+/// This `struct` is created by the [`iter`] method on [`HashMap`]. See its
+/// documentation for more.
+///
+/// [`iter`]: struct.HashMap.html#method.iter
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let map: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut iter = map.iter();
+/// let mut vec = vec![iter.next(), iter.next(), iter.next()];
+///
+/// // The `Iter` iterator produces items in arbitrary order, so the
+/// // items must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some((&1, &"a")), Some((&2, &"b")), Some((&3, &"c"))]);
+///
+/// // It is fused iterator
+/// assert_eq!(iter.next(), None);
+/// assert_eq!(iter.next(), None);
+/// ```
+pub struct Iter<'a, K, V> {
+    inner: RawIter<(K, V)>,
+    marker: PhantomData<(&'a K, &'a V)>,
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Iter<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone(),
+            marker: PhantomData,
+        }
+    }
+}
+
+impl<K: Debug, V: Debug> fmt::Debug for Iter<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A mutable iterator over the entries of a `HashMap` in arbitrary order.
+/// The iterator element type is `(&'a K, &'a mut V)`.
+///
+/// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its
+/// documentation for more.
+///
+/// [`iter_mut`]: struct.HashMap.html#method.iter_mut
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let mut map: HashMap<_, _> = [(1, "One".to_owned()), (2, "Two".into())].into();
+///
+/// let mut iter = map.iter_mut();
+/// iter.next().map(|(_, v)| v.push_str(" Mississippi"));
+/// iter.next().map(|(_, v)| v.push_str(" Mississippi"));
+///
+/// // It is fused iterator
+/// assert_eq!(iter.next(), None);
+/// assert_eq!(iter.next(), None);
+///
+/// assert_eq!(map.get(&1).unwrap(), &"One Mississippi".to_owned());
+/// assert_eq!(map.get(&2).unwrap(), &"Two Mississippi".to_owned());
+/// ```
+pub struct IterMut<'a, K, V> {
+    inner: RawIter<(K, V)>,
+    // To ensure invariance with respect to V
+    marker: PhantomData<(&'a K, &'a mut V)>,
+}
+
+// We override the default Send impl which has K: Sync instead of K: Send. Both
+// are correct, but this one is more general since it allows keys which
+// implement Send but not Sync.
+unsafe impl<K: Send, V: Send> Send for IterMut<'_, K, V> {}
+
+impl<K, V> IterMut<'_, K, V> {
+    /// Returns a iterator of references over the remaining items.
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub(super) fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            inner: self.inner.clone(),
+            marker: PhantomData,
+        }
+    }
+}
+
+/// An owning iterator over the entries of a `HashMap` in arbitrary order.
+/// The iterator element type is `(K, V)`.
+///
+/// This `struct` is created by the [`into_iter`] method on [`HashMap`]
+/// (provided by the [`IntoIterator`] trait). See its documentation for more.
+/// The map cannot be used after calling that method.
+///
+/// [`into_iter`]: struct.HashMap.html#method.into_iter
+/// [`HashMap`]: struct.HashMap.html
+/// [`IntoIterator`]: https://doc.rust-lang.org/core/iter/trait.IntoIterator.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let map: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut iter = map.into_iter();
+/// let mut vec = vec![iter.next(), iter.next(), iter.next()];
+///
+/// // The `IntoIter` iterator produces items in arbitrary order, so the
+/// // items must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some((1, "a")), Some((2, "b")), Some((3, "c"))]);
+///
+/// // It is fused iterator
+/// assert_eq!(iter.next(), None);
+/// assert_eq!(iter.next(), None);
+/// ```
+pub struct IntoIter<K, V, A: Allocator + Clone = Global> {
+    inner: RawIntoIter<(K, V), A>,
+}
+
+impl<K, V, A: Allocator + Clone> IntoIter<K, V, A> {
+    /// Returns a iterator of references over the remaining items.
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub(super) fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            inner: self.inner.iter(),
+            marker: PhantomData,
+        }
+    }
+}
+
+/// An owning iterator over the keys of a `HashMap` in arbitrary order.
+/// The iterator element type is `K`.
+///
+/// This `struct` is created by the [`into_keys`] method on [`HashMap`].
+/// See its documentation for more.
+/// The map cannot be used after calling that method.
+///
+/// [`into_keys`]: struct.HashMap.html#method.into_keys
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let map: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut keys = map.into_keys();
+/// let mut vec = vec![keys.next(), keys.next(), keys.next()];
+///
+/// // The `IntoKeys` iterator produces keys in arbitrary order, so the
+/// // keys must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some(1), Some(2), Some(3)]);
+///
+/// // It is fused iterator
+/// assert_eq!(keys.next(), None);
+/// assert_eq!(keys.next(), None);
+/// ```
+pub struct IntoKeys<K, V, A: Allocator + Clone = Global> {
+    inner: IntoIter<K, V, A>,
+}
+
+impl<K, V, A: Allocator + Clone> Iterator for IntoKeys<K, V, A> {
+    type Item = K;
+
+    #[inline]
+    fn next(&mut self) -> Option<K> {
+        self.inner.next().map(|(k, _)| k)
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoKeys<K, V, A> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<K, V, A: Allocator + Clone> FusedIterator for IntoKeys<K, V, A> {}
+
+impl<K: Debug, V: Debug, A: Allocator + Clone> fmt::Debug for IntoKeys<K, V, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entries(self.inner.iter().map(|(k, _)| k))
+            .finish()
+    }
+}
+
+/// An owning iterator over the values of a `HashMap` in arbitrary order.
+/// The iterator element type is `V`.
+///
+/// This `struct` is created by the [`into_values`] method on [`HashMap`].
+/// See its documentation for more. The map cannot be used after calling that method.
+///
+/// [`into_values`]: struct.HashMap.html#method.into_values
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let map: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut values = map.into_values();
+/// let mut vec = vec![values.next(), values.next(), values.next()];
+///
+/// // The `IntoValues` iterator produces values in arbitrary order, so
+/// // the values must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some("a"), Some("b"), Some("c")]);
+///
+/// // It is fused iterator
+/// assert_eq!(values.next(), None);
+/// assert_eq!(values.next(), None);
+/// ```
+pub struct IntoValues<K, V, A: Allocator + Clone = Global> {
+    inner: IntoIter<K, V, A>,
+}
+
+impl<K, V, A: Allocator + Clone> Iterator for IntoValues<K, V, A> {
+    type Item = V;
+
+    #[inline]
+    fn next(&mut self) -> Option<V> {
+        self.inner.next().map(|(_, v)| v)
+    }
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+
+impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoValues<K, V, A> {
+    #[inline]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<K, V, A: Allocator + Clone> FusedIterator for IntoValues<K, V, A> {}
+
+impl<K, V: Debug, A: Allocator + Clone> fmt::Debug for IntoValues<K, V, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entries(self.inner.iter().map(|(_, v)| v))
+            .finish()
+    }
+}
+
+/// An iterator over the keys of a `HashMap` in arbitrary order.
+/// The iterator element type is `&'a K`.
+///
+/// This `struct` is created by the [`keys`] method on [`HashMap`]. See its
+/// documentation for more.
+///
+/// [`keys`]: struct.HashMap.html#method.keys
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let map: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut keys = map.keys();
+/// let mut vec = vec![keys.next(), keys.next(), keys.next()];
+///
+/// // The `Keys` iterator produces keys in arbitrary order, so the
+/// // keys must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some(&1), Some(&2), Some(&3)]);
+///
+/// // It is fused iterator
+/// assert_eq!(keys.next(), None);
+/// assert_eq!(keys.next(), None);
+/// ```
+pub struct Keys<'a, K, V> {
+    inner: Iter<'a, K, V>,
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Keys<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        Keys {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<K: Debug, V> fmt::Debug for Keys<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// An iterator over the values of a `HashMap` in arbitrary order.
+/// The iterator element type is `&'a V`.
+///
+/// This `struct` is created by the [`values`] method on [`HashMap`]. See its
+/// documentation for more.
+///
+/// [`values`]: struct.HashMap.html#method.values
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let map: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut values = map.values();
+/// let mut vec = vec![values.next(), values.next(), values.next()];
+///
+/// // The `Values` iterator produces values in arbitrary order, so the
+/// // values must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some(&"a"), Some(&"b"), Some(&"c")]);
+///
+/// // It is fused iterator
+/// assert_eq!(values.next(), None);
+/// assert_eq!(values.next(), None);
+/// ```
+pub struct Values<'a, K, V> {
+    inner: Iter<'a, K, V>,
+}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Values<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        Values {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+impl<K, V: Debug> fmt::Debug for Values<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A draining iterator over the entries of a `HashMap` in arbitrary
+/// order. The iterator element type is `(K, V)`.
+///
+/// This `struct` is created by the [`drain`] method on [`HashMap`]. See its
+/// documentation for more.
+///
+/// [`drain`]: struct.HashMap.html#method.drain
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let mut map: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut drain_iter = map.drain();
+/// let mut vec = vec![drain_iter.next(), drain_iter.next(), drain_iter.next()];
+///
+/// // The `Drain` iterator produces items in arbitrary order, so the
+/// // items must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some((1, "a")), Some((2, "b")), Some((3, "c"))]);
+///
+/// // It is fused iterator
+/// assert_eq!(drain_iter.next(), None);
+/// assert_eq!(drain_iter.next(), None);
+/// ```
+pub struct Drain<'a, K, V, A: Allocator + Clone = Global> {
+    inner: RawDrain<'a, (K, V), A>,
+}
+
+impl<K, V, A: Allocator + Clone> Drain<'_, K, V, A> {
+    /// Returns a iterator of references over the remaining items.
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub(super) fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            inner: self.inner.iter(),
+            marker: PhantomData,
+        }
+    }
+}
+
+/// A draining iterator over entries of a `HashMap` which don't satisfy the predicate
+/// `f(&k, &mut v)` in arbitrary order. The iterator element type is `(K, V)`.
+///
+/// This `struct` is created by the [`drain_filter`] method on [`HashMap`]. See its
+/// documentation for more.
+///
+/// [`drain_filter`]: struct.HashMap.html#method.drain_filter
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let mut map: HashMap<i32, &str> = [(1, "a"), (2, "b"), (3, "c")].into();
+///
+/// let mut drain_filter = map.drain_filter(|k, _v| k % 2 != 0);
+/// let mut vec = vec![drain_filter.next(), drain_filter.next()];
+///
+/// // The `DrainFilter` iterator produces items in arbitrary order, so the
+/// // items must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [Some((1, "a")),Some((3, "c"))]);
+///
+/// // It is fused iterator
+/// assert_eq!(drain_filter.next(), None);
+/// assert_eq!(drain_filter.next(), None);
+/// drop(drain_filter);
+///
+/// assert_eq!(map.len(), 1);
+/// ```
+pub struct DrainFilter<'a, K, V, F, A: Allocator + Clone = Global>
+where
+    F: FnMut(&K, &mut V) -> bool,
+{
+    f: F,
+    inner: DrainFilterInner<'a, K, V, A>,
+}
+
+impl<'a, K, V, F, A> Drop for DrainFilter<'a, K, V, F, A>
+where
+    F: FnMut(&K, &mut V) -> bool,
+    A: Allocator + Clone,
+{
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn drop(&mut self) {
+        while let Some(item) = self.next() {
+            let guard = ConsumeAllOnDrop(self);
+            drop(item);
+            mem::forget(guard);
+        }
+    }
+}
+
+pub(super) struct ConsumeAllOnDrop<'a, T: Iterator>(pub &'a mut T);
+
+impl<T: Iterator> Drop for ConsumeAllOnDrop<'_, T> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn drop(&mut self) {
+        self.0.for_each(drop);
+    }
+}
+
+impl<K, V, F, A> Iterator for DrainFilter<'_, K, V, F, A>
+where
+    F: FnMut(&K, &mut V) -> bool,
+    A: Allocator + Clone,
+{
+    type Item = (K, V);
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next(&mut self.f)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, self.inner.iter.size_hint().1)
+    }
+}
+
+impl<K, V, F> FusedIterator for DrainFilter<'_, K, V, F> where F: FnMut(&K, &mut V) -> bool {}
+
+/// Portions of `DrainFilter` shared with `set::DrainFilter`
+pub(super) struct DrainFilterInner<'a, K, V, A: Allocator + Clone> {
+    pub iter: RawIter<(K, V)>,
+    pub table: &'a mut RawTable<(K, V), A>,
+}
+
+impl<K, V, A: Allocator + Clone> DrainFilterInner<'_, K, V, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub(super) fn next<F>(&mut self, f: &mut F) -> Option<(K, V)>
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        unsafe {
+            for item in &mut self.iter {
+                let &mut (ref key, ref mut value) = item.as_mut();
+                if f(key, value) {
+                    return Some(self.table.remove(item));
+                }
+            }
+        }
+        None
+    }
+}
+
+/// A mutable iterator over the values of a `HashMap` in arbitrary order.
+/// The iterator element type is `&'a mut V`.
+///
+/// This `struct` is created by the [`values_mut`] method on [`HashMap`]. See its
+/// documentation for more.
+///
+/// [`values_mut`]: struct.HashMap.html#method.values_mut
+/// [`HashMap`]: struct.HashMap.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashMap;
+///
+/// let mut map: HashMap<_, _> = [(1, "One".to_owned()), (2, "Two".into())].into();
+///
+/// let mut values = map.values_mut();
+/// values.next().map(|v| v.push_str(" Mississippi"));
+/// values.next().map(|v| v.push_str(" Mississippi"));
+///
+/// // It is fused iterator
+/// assert_eq!(values.next(), None);
+/// assert_eq!(values.next(), None);
+///
+/// assert_eq!(map.get(&1).unwrap(), &"One Mississippi".to_owned());
+/// assert_eq!(map.get(&2).unwrap(), &"Two Mississippi".to_owned());
+/// ```
+pub struct ValuesMut<'a, K, V> {
+    inner: IterMut<'a, K, V>,
+}
+
+/// A builder for computing where in a [`HashMap`] a key-value pair would be stored.
+///
+/// See the [`HashMap::raw_entry_mut`] docs for usage examples.
+///
+/// [`HashMap::raw_entry_mut`]: struct.HashMap.html#method.raw_entry_mut
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{RawEntryBuilderMut, RawEntryMut::Vacant, RawEntryMut::Occupied};
+/// use hashbrown::HashMap;
+/// use core::hash::{BuildHasher, Hash};
+///
+/// let mut map = HashMap::new();
+/// map.extend([(1, 11), (2, 12), (3, 13), (4, 14), (5, 15), (6, 16)]);
+/// assert_eq!(map.len(), 6);
+///
+/// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+///     use core::hash::Hasher;
+///     let mut state = hash_builder.build_hasher();
+///     key.hash(&mut state);
+///     state.finish()
+/// }
+///
+/// let builder: RawEntryBuilderMut<_, _, _> = map.raw_entry_mut();
+///
+/// // Existing key
+/// match builder.from_key(&6) {
+///     Vacant(_) => unreachable!(),
+///     Occupied(view) => assert_eq!(view.get(), &16),
+/// }
+///
+/// for key in 0..12 {
+///     let hash = compute_hash(map.hasher(), &key);
+///     let value = map.get(&key).cloned();
+///     let key_value = value.as_ref().map(|v| (&key, v));
+///
+///     println!("Key: {} and value: {:?}", key, value);
+///
+///     match map.raw_entry_mut().from_key(&key) {
+///         Occupied(mut o) => assert_eq!(Some(o.get_key_value()), key_value),
+///         Vacant(_) => assert_eq!(value, None),
+///     }
+///     match map.raw_entry_mut().from_key_hashed_nocheck(hash, &key) {
+///         Occupied(mut o) => assert_eq!(Some(o.get_key_value()), key_value),
+///         Vacant(_) => assert_eq!(value, None),
+///     }
+///     match map.raw_entry_mut().from_hash(hash, |q| *q == key) {
+///         Occupied(mut o) => assert_eq!(Some(o.get_key_value()), key_value),
+///         Vacant(_) => assert_eq!(value, None),
+///     }
+/// }
+///
+/// assert_eq!(map.len(), 6);
+/// ```
+pub struct RawEntryBuilderMut<'a, K, V, S, A: Allocator + Clone = Global> {
+    map: &'a mut HashMap<K, V, S, A>,
+}
+
+/// A view into a single entry in a map, which may either be vacant or occupied.
+///
+/// This is a lower-level version of [`Entry`].
+///
+/// This `enum` is constructed through the [`raw_entry_mut`] method on [`HashMap`],
+/// then calling one of the methods of that [`RawEntryBuilderMut`].
+///
+/// [`HashMap`]: struct.HashMap.html
+/// [`Entry`]: enum.Entry.html
+/// [`raw_entry_mut`]: struct.HashMap.html#method.raw_entry_mut
+/// [`RawEntryBuilderMut`]: struct.RawEntryBuilderMut.html
+///
+/// # Examples
+///
+/// ```
+/// use core::hash::{BuildHasher, Hash};
+/// use hashbrown::hash_map::{HashMap, RawEntryMut, RawOccupiedEntryMut};
+///
+/// let mut map = HashMap::new();
+/// map.extend([('a', 1), ('b', 2), ('c', 3)]);
+/// assert_eq!(map.len(), 3);
+///
+/// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+///     use core::hash::Hasher;
+///     let mut state = hash_builder.build_hasher();
+///     key.hash(&mut state);
+///     state.finish()
+/// }
+///
+/// // Existing key (insert)
+/// let raw: RawEntryMut<_, _, _> = map.raw_entry_mut().from_key(&'a');
+/// let _raw_o: RawOccupiedEntryMut<_, _, _> = raw.insert('a', 10);
+/// assert_eq!(map.len(), 3);
+///
+/// // Nonexistent key (insert)
+/// map.raw_entry_mut().from_key(&'d').insert('d', 40);
+/// assert_eq!(map.len(), 4);
+///
+/// // Existing key (or_insert)
+/// let hash = compute_hash(map.hasher(), &'b');
+/// let kv = map
+///     .raw_entry_mut()
+///     .from_key_hashed_nocheck(hash, &'b')
+///     .or_insert('b', 20);
+/// assert_eq!(kv, (&mut 'b', &mut 2));
+/// *kv.1 = 20;
+/// assert_eq!(map.len(), 4);
+///
+/// // Nonexistent key (or_insert)
+/// let hash = compute_hash(map.hasher(), &'e');
+/// let kv = map
+///     .raw_entry_mut()
+///     .from_key_hashed_nocheck(hash, &'e')
+///     .or_insert('e', 50);
+/// assert_eq!(kv, (&mut 'e', &mut 50));
+/// assert_eq!(map.len(), 5);
+///
+/// // Existing key (or_insert_with)
+/// let hash = compute_hash(map.hasher(), &'c');
+/// let kv = map
+///     .raw_entry_mut()
+///     .from_hash(hash, |q| q == &'c')
+///     .or_insert_with(|| ('c', 30));
+/// assert_eq!(kv, (&mut 'c', &mut 3));
+/// *kv.1 = 30;
+/// assert_eq!(map.len(), 5);
+///
+/// // Nonexistent key (or_insert_with)
+/// let hash = compute_hash(map.hasher(), &'f');
+/// let kv = map
+///     .raw_entry_mut()
+///     .from_hash(hash, |q| q == &'f')
+///     .or_insert_with(|| ('f', 60));
+/// assert_eq!(kv, (&mut 'f', &mut 60));
+/// assert_eq!(map.len(), 6);
+///
+/// println!("Our HashMap: {:?}", map);
+///
+/// let mut vec: Vec<_> = map.iter().map(|(&k, &v)| (k, v)).collect();
+/// // The `Iter` iterator produces items in arbitrary order, so the
+/// // items must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [('a', 10), ('b', 20), ('c', 30), ('d', 40), ('e', 50), ('f', 60)]);
+/// ```
+pub enum RawEntryMut<'a, K, V, S, A: Allocator + Clone = Global> {
+    /// An occupied entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::{hash_map::RawEntryMut, HashMap};
+    /// let mut map: HashMap<_, _> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => unreachable!(),
+    ///     RawEntryMut::Occupied(_) => { }
+    /// }
+    /// ```
+    Occupied(RawOccupiedEntryMut<'a, K, V, S, A>),
+    /// A vacant entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::{hash_map::RawEntryMut, HashMap};
+    /// let mut map: HashMap<&str, i32> = HashMap::new();
+    ///
+    /// match map.raw_entry_mut().from_key("a") {
+    ///     RawEntryMut::Occupied(_) => unreachable!(),
+    ///     RawEntryMut::Vacant(_) => { }
+    /// }
+    /// ```
+    Vacant(RawVacantEntryMut<'a, K, V, S, A>),
+}
+
+/// A view into an occupied entry in a `HashMap`.
+/// It is part of the [`RawEntryMut`] enum.
+///
+/// [`RawEntryMut`]: enum.RawEntryMut.html
+///
+/// # Examples
+///
+/// ```
+/// use core::hash::{BuildHasher, Hash};
+/// use hashbrown::hash_map::{HashMap, RawEntryMut, RawOccupiedEntryMut};
+///
+/// let mut map = HashMap::new();
+/// map.extend([("a", 10), ("b", 20), ("c", 30)]);
+///
+/// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+///     use core::hash::Hasher;
+///     let mut state = hash_builder.build_hasher();
+///     key.hash(&mut state);
+///     state.finish()
+/// }
+///
+/// let _raw_o: RawOccupiedEntryMut<_, _, _> = map.raw_entry_mut().from_key(&"a").insert("a", 100);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (insert and update)
+/// match map.raw_entry_mut().from_key(&"a") {
+///     RawEntryMut::Vacant(_) => unreachable!(),
+///     RawEntryMut::Occupied(mut view) => {
+///         assert_eq!(view.get(), &100);
+///         let v = view.get_mut();
+///         let new_v = (*v) * 10;
+///         *v = new_v;
+///         assert_eq!(view.insert(1111), 1000);
+///     }
+/// }
+///
+/// assert_eq!(map[&"a"], 1111);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (take)
+/// let hash = compute_hash(map.hasher(), &"c");
+/// match map.raw_entry_mut().from_key_hashed_nocheck(hash, &"c") {
+///     RawEntryMut::Vacant(_) => unreachable!(),
+///     RawEntryMut::Occupied(view) => {
+///         assert_eq!(view.remove_entry(), ("c", 30));
+///     }
+/// }
+/// assert_eq!(map.raw_entry().from_key(&"c"), None);
+/// assert_eq!(map.len(), 2);
+///
+/// let hash = compute_hash(map.hasher(), &"b");
+/// match map.raw_entry_mut().from_hash(hash, |q| *q == "b") {
+///     RawEntryMut::Vacant(_) => unreachable!(),
+///     RawEntryMut::Occupied(view) => {
+///         assert_eq!(view.remove_entry(), ("b", 20));
+///     }
+/// }
+/// assert_eq!(map.get(&"b"), None);
+/// assert_eq!(map.len(), 1);
+/// ```
+pub struct RawOccupiedEntryMut<'a, K, V, S, A: Allocator + Clone = Global> {
+    elem: Bucket<(K, V)>,
+    table: &'a mut RawTable<(K, V), A>,
+    hash_builder: &'a S,
+}
+
+unsafe impl<K, V, S, A> Send for RawOccupiedEntryMut<'_, K, V, S, A>
+where
+    K: Send,
+    V: Send,
+    S: Send,
+    A: Send + Allocator + Clone,
+{
+}
+unsafe impl<K, V, S, A> Sync for RawOccupiedEntryMut<'_, K, V, S, A>
+where
+    K: Sync,
+    V: Sync,
+    S: Sync,
+    A: Sync + Allocator + Clone,
+{
+}
+
+/// A view into a vacant entry in a `HashMap`.
+/// It is part of the [`RawEntryMut`] enum.
+///
+/// [`RawEntryMut`]: enum.RawEntryMut.html
+///
+/// # Examples
+///
+/// ```
+/// use core::hash::{BuildHasher, Hash};
+/// use hashbrown::hash_map::{HashMap, RawEntryMut, RawVacantEntryMut};
+///
+/// let mut map = HashMap::<&str, i32>::new();
+///
+/// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+///     use core::hash::Hasher;
+///     let mut state = hash_builder.build_hasher();
+///     key.hash(&mut state);
+///     state.finish()
+/// }
+///
+/// let raw_v: RawVacantEntryMut<_, _, _> = match map.raw_entry_mut().from_key(&"a") {
+///     RawEntryMut::Vacant(view) => view,
+///     RawEntryMut::Occupied(_) => unreachable!(),
+/// };
+/// raw_v.insert("a", 10);
+/// assert!(map[&"a"] == 10 && map.len() == 1);
+///
+/// // Nonexistent key (insert and update)
+/// let hash = compute_hash(map.hasher(), &"b");
+/// match map.raw_entry_mut().from_key_hashed_nocheck(hash, &"b") {
+///     RawEntryMut::Occupied(_) => unreachable!(),
+///     RawEntryMut::Vacant(view) => {
+///         let (k, value) = view.insert("b", 2);
+///         assert_eq!((*k, *value), ("b", 2));
+///         *value = 20;
+///     }
+/// }
+/// assert!(map[&"b"] == 20 && map.len() == 2);
+///
+/// let hash = compute_hash(map.hasher(), &"c");
+/// match map.raw_entry_mut().from_hash(hash, |q| *q == "c") {
+///     RawEntryMut::Occupied(_) => unreachable!(),
+///     RawEntryMut::Vacant(view) => {
+///         assert_eq!(view.insert("c", 30), (&mut "c", &mut 30));
+///     }
+/// }
+/// assert!(map[&"c"] == 30 && map.len() == 3);
+/// ```
+pub struct RawVacantEntryMut<'a, K, V, S, A: Allocator + Clone = Global> {
+    table: &'a mut RawTable<(K, V), A>,
+    hash_builder: &'a S,
+}
+
+/// A builder for computing where in a [`HashMap`] a key-value pair would be stored.
+///
+/// See the [`HashMap::raw_entry`] docs for usage examples.
+///
+/// [`HashMap::raw_entry`]: struct.HashMap.html#method.raw_entry
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{HashMap, RawEntryBuilder};
+/// use core::hash::{BuildHasher, Hash};
+///
+/// let mut map = HashMap::new();
+/// map.extend([(1, 10), (2, 20), (3, 30)]);
+///
+/// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+///     use core::hash::Hasher;
+///     let mut state = hash_builder.build_hasher();
+///     key.hash(&mut state);
+///     state.finish()
+/// }
+///
+/// for k in 0..6 {
+///     let hash = compute_hash(map.hasher(), &k);
+///     let v = map.get(&k).cloned();
+///     let kv = v.as_ref().map(|v| (&k, v));
+///
+///     println!("Key: {} and value: {:?}", k, v);
+///     let builder: RawEntryBuilder<_, _, _> = map.raw_entry();
+///     assert_eq!(builder.from_key(&k), kv);
+///     assert_eq!(map.raw_entry().from_hash(hash, |q| *q == k), kv);
+///     assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash, &k), kv);
+/// }
+/// ```
+pub struct RawEntryBuilder<'a, K, V, S, A: Allocator + Clone = Global> {
+    map: &'a HashMap<K, V, S, A>,
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> RawEntryBuilderMut<'a, K, V, S, A> {
+    /// Creates a `RawEntryMut` from the given key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// let key = "a";
+    /// let entry: RawEntryMut<&str, u32, _> = map.raw_entry_mut().from_key(&key);
+    /// entry.insert(key, 100);
+    /// assert_eq!(map[&"a"], 100);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    #[allow(clippy::wrong_self_convention)]
+    pub fn from_key<Q: ?Sized>(self, k: &Q) -> RawEntryMut<'a, K, V, S, A>
+    where
+        S: BuildHasher,
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        let hash = make_hash::<K, Q, S>(&self.map.hash_builder, k);
+        self.from_key_hashed_nocheck(hash, k)
+    }
+
+    /// Creates a `RawEntryMut` from the given key and its hash.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// let key = "a";
+    /// let hash = compute_hash(map.hasher(), &key);
+    /// let entry: RawEntryMut<&str, u32, _> = map.raw_entry_mut().from_key_hashed_nocheck(hash, &key);
+    /// entry.insert(key, 100);
+    /// assert_eq!(map[&"a"], 100);
+    /// ```
+    #[inline]
+    #[allow(clippy::wrong_self_convention)]
+    pub fn from_key_hashed_nocheck<Q: ?Sized>(self, hash: u64, k: &Q) -> RawEntryMut<'a, K, V, S, A>
+    where
+        K: Borrow<Q>,
+        Q: Eq,
+    {
+        self.from_hash(hash, equivalent(k))
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> RawEntryBuilderMut<'a, K, V, S, A> {
+    /// Creates a `RawEntryMut` from the given hash and matching function.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// let key = "a";
+    /// let hash = compute_hash(map.hasher(), &key);
+    /// let entry: RawEntryMut<&str, u32, _> = map.raw_entry_mut().from_hash(hash, |k| k == &key);
+    /// entry.insert(key, 100);
+    /// assert_eq!(map[&"a"], 100);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    #[allow(clippy::wrong_self_convention)]
+    pub fn from_hash<F>(self, hash: u64, is_match: F) -> RawEntryMut<'a, K, V, S, A>
+    where
+        for<'b> F: FnMut(&'b K) -> bool,
+    {
+        self.search(hash, is_match)
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn search<F>(self, hash: u64, mut is_match: F) -> RawEntryMut<'a, K, V, S, A>
+    where
+        for<'b> F: FnMut(&'b K) -> bool,
+    {
+        match self.map.table.find(hash, |(k, _)| is_match(k)) {
+            Some(elem) => RawEntryMut::Occupied(RawOccupiedEntryMut {
+                elem,
+                table: &mut self.map.table,
+                hash_builder: &self.map.hash_builder,
+            }),
+            None => RawEntryMut::Vacant(RawVacantEntryMut {
+                table: &mut self.map.table,
+                hash_builder: &self.map.hash_builder,
+            }),
+        }
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> RawEntryBuilder<'a, K, V, S, A> {
+    /// Access an immutable entry by key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    /// let key = "a";
+    /// assert_eq!(map.raw_entry().from_key(&key), Some((&"a", &100)));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    #[allow(clippy::wrong_self_convention)]
+    pub fn from_key<Q: ?Sized>(self, k: &Q) -> Option<(&'a K, &'a V)>
+    where
+        S: BuildHasher,
+        K: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        let hash = make_hash::<K, Q, S>(&self.map.hash_builder, k);
+        self.from_key_hashed_nocheck(hash, k)
+    }
+
+    /// Access an immutable entry by a key and its hash.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::HashMap;
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// let map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    /// let key = "a";
+    /// let hash = compute_hash(map.hasher(), &key);
+    /// assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash, &key), Some((&"a", &100)));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    #[allow(clippy::wrong_self_convention)]
+    pub fn from_key_hashed_nocheck<Q: ?Sized>(self, hash: u64, k: &Q) -> Option<(&'a K, &'a V)>
+    where
+        K: Borrow<Q>,
+        Q: Eq,
+    {
+        self.from_hash(hash, equivalent(k))
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn search<F>(self, hash: u64, mut is_match: F) -> Option<(&'a K, &'a V)>
+    where
+        F: FnMut(&K) -> bool,
+    {
+        match self.map.table.get(hash, |(k, _)| is_match(k)) {
+            Some(&(ref key, ref value)) => Some((key, value)),
+            None => None,
+        }
+    }
+
+    /// Access an immutable entry by hash and matching function.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::HashMap;
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// let map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    /// let key = "a";
+    /// let hash = compute_hash(map.hasher(), &key);
+    /// assert_eq!(map.raw_entry().from_hash(hash, |k| k == &key), Some((&"a", &100)));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    #[allow(clippy::wrong_self_convention)]
+    pub fn from_hash<F>(self, hash: u64, is_match: F) -> Option<(&'a K, &'a V)>
+    where
+        F: FnMut(&K) -> bool,
+    {
+        self.search(hash, is_match)
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> RawEntryMut<'a, K, V, S, A> {
+    /// Sets the value of the entry, and returns a RawOccupiedEntryMut.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// let entry = map.raw_entry_mut().from_key("horseyland").insert("horseyland", 37);
+    ///
+    /// assert_eq!(entry.remove_entry(), ("horseyland", 37));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self, key: K, value: V) -> RawOccupiedEntryMut<'a, K, V, S, A>
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            RawEntryMut::Occupied(mut entry) => {
+                entry.insert(value);
+                entry
+            }
+            RawEntryMut::Vacant(entry) => entry.insert_entry(key, value),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the default if empty, and returns
+    /// mutable references to the key and value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// map.raw_entry_mut().from_key("poneyland").or_insert("poneyland", 3);
+    /// assert_eq!(map["poneyland"], 3);
+    ///
+    /// *map.raw_entry_mut().from_key("poneyland").or_insert("poneyland", 10).1 *= 2;
+    /// assert_eq!(map["poneyland"], 6);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert(self, default_key: K, default_val: V) -> (&'a mut K, &'a mut V)
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            RawEntryMut::Occupied(entry) => entry.into_key_value(),
+            RawEntryMut::Vacant(entry) => entry.insert(default_key, default_val),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the result of the default function if empty,
+    /// and returns mutable references to the key and value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, String> = HashMap::new();
+    ///
+    /// map.raw_entry_mut().from_key("poneyland").or_insert_with(|| {
+    ///     ("poneyland", "hoho".to_string())
+    /// });
+    ///
+    /// assert_eq!(map["poneyland"], "hoho".to_string());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert_with<F>(self, default: F) -> (&'a mut K, &'a mut V)
+    where
+        F: FnOnce() -> (K, V),
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            RawEntryMut::Occupied(entry) => entry.into_key_value(),
+            RawEntryMut::Vacant(entry) => {
+                let (k, v) = default();
+                entry.insert(k, v)
+            }
+        }
+    }
+
+    /// Provides in-place mutable access to an occupied entry before any
+    /// potential inserts into the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// map.raw_entry_mut()
+    ///    .from_key("poneyland")
+    ///    .and_modify(|_k, v| { *v += 1 })
+    ///    .or_insert("poneyland", 42);
+    /// assert_eq!(map["poneyland"], 42);
+    ///
+    /// map.raw_entry_mut()
+    ///    .from_key("poneyland")
+    ///    .and_modify(|_k, v| { *v += 1 })
+    ///    .or_insert("poneyland", 0);
+    /// assert_eq!(map["poneyland"], 43);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn and_modify<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&mut K, &mut V),
+    {
+        match self {
+            RawEntryMut::Occupied(mut entry) => {
+                {
+                    let (k, v) = entry.get_key_value_mut();
+                    f(k, v);
+                }
+                RawEntryMut::Occupied(entry)
+            }
+            RawEntryMut::Vacant(entry) => RawEntryMut::Vacant(entry),
+        }
+    }
+
+    /// Provides shared access to the key and owned access to the value of
+    /// an occupied entry and allows to replace or remove it based on the
+    /// value of the returned option.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::RawEntryMut;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// let entry = map
+    ///     .raw_entry_mut()
+    ///     .from_key("poneyland")
+    ///     .and_replace_entry_with(|_k, _v| panic!());
+    ///
+    /// match entry {
+    ///     RawEntryMut::Vacant(_) => {},
+    ///     RawEntryMut::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// map.insert("poneyland", 42);
+    ///
+    /// let entry = map
+    ///     .raw_entry_mut()
+    ///     .from_key("poneyland")
+    ///     .and_replace_entry_with(|k, v| {
+    ///         assert_eq!(k, &"poneyland");
+    ///         assert_eq!(v, 42);
+    ///         Some(v + 1)
+    ///     });
+    ///
+    /// match entry {
+    ///     RawEntryMut::Occupied(e) => {
+    ///         assert_eq!(e.key(), &"poneyland");
+    ///         assert_eq!(e.get(), &43);
+    ///     },
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 43);
+    ///
+    /// let entry = map
+    ///     .raw_entry_mut()
+    ///     .from_key("poneyland")
+    ///     .and_replace_entry_with(|_k, _v| None);
+    ///
+    /// match entry {
+    ///     RawEntryMut::Vacant(_) => {},
+    ///     RawEntryMut::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// assert!(!map.contains_key("poneyland"));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn and_replace_entry_with<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&K, V) -> Option<V>,
+    {
+        match self {
+            RawEntryMut::Occupied(entry) => entry.replace_entry_with(f),
+            RawEntryMut::Vacant(_) => self,
+        }
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> RawOccupiedEntryMut<'a, K, V, S, A> {
+    /// Gets a reference to the key in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => assert_eq!(o.key(), &"a")
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key(&self) -> &K {
+        unsafe { &self.elem.as_ref().0 }
+    }
+
+    /// Gets a mutable reference to the key in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    /// use std::rc::Rc;
+    ///
+    /// let key_one = Rc::new("a");
+    /// let key_two = Rc::new("a");
+    ///
+    /// let mut map: HashMap<Rc<&str>, u32> = HashMap::new();
+    /// map.insert(key_one.clone(), 10);
+    ///
+    /// assert_eq!(map[&key_one], 10);
+    /// assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);
+    ///
+    /// match map.raw_entry_mut().from_key(&key_one) {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(mut o) => {
+    ///         *o.key_mut() = key_two.clone();
+    ///     }
+    /// }
+    /// assert_eq!(map[&key_two], 10);
+    /// assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key_mut(&mut self) -> &mut K {
+        unsafe { &mut self.elem.as_mut().0 }
+    }
+
+    /// Converts the entry into a mutable reference to the key in the entry
+    /// with a lifetime bound to the map itself.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    /// use std::rc::Rc;
+    ///
+    /// let key_one = Rc::new("a");
+    /// let key_two = Rc::new("a");
+    ///
+    /// let mut map: HashMap<Rc<&str>, u32> = HashMap::new();
+    /// map.insert(key_one.clone(), 10);
+    ///
+    /// assert_eq!(map[&key_one], 10);
+    /// assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);
+    ///
+    /// let inside_key: &mut Rc<&str>;
+    ///
+    /// match map.raw_entry_mut().from_key(&key_one) {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => inside_key = o.into_key(),
+    /// }
+    /// *inside_key = key_two.clone();
+    ///
+    /// assert_eq!(map[&key_two], 10);
+    /// assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_key(self) -> &'a mut K {
+        unsafe { &mut self.elem.as_mut().0 }
+    }
+
+    /// Gets a reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => assert_eq!(o.get(), &100),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get(&self) -> &V {
+        unsafe { &self.elem.as_ref().1 }
+    }
+
+    /// Converts the OccupiedEntry into a mutable reference to the value in the entry
+    /// with a lifetime bound to the map itself.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// let value: &mut u32;
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => value = o.into_mut(),
+    /// }
+    /// *value += 900;
+    ///
+    /// assert_eq!(map[&"a"], 1000);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_mut(self) -> &'a mut V {
+        unsafe { &mut self.elem.as_mut().1 }
+    }
+
+    /// Gets a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(mut o) => *o.get_mut() += 900,
+    /// }
+    ///
+    /// assert_eq!(map[&"a"], 1000);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_mut(&mut self) -> &mut V {
+        unsafe { &mut self.elem.as_mut().1 }
+    }
+
+    /// Gets a reference to the key and value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => assert_eq!(o.get_key_value(), (&"a", &100)),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_key_value(&self) -> (&K, &V) {
+        unsafe {
+            let &(ref key, ref value) = self.elem.as_ref();
+            (key, value)
+        }
+    }
+
+    /// Gets a mutable reference to the key and value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    /// use std::rc::Rc;
+    ///
+    /// let key_one = Rc::new("a");
+    /// let key_two = Rc::new("a");
+    ///
+    /// let mut map: HashMap<Rc<&str>, u32> = HashMap::new();
+    /// map.insert(key_one.clone(), 10);
+    ///
+    /// assert_eq!(map[&key_one], 10);
+    /// assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);
+    ///
+    /// match map.raw_entry_mut().from_key(&key_one) {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(mut o) => {
+    ///         let (inside_key, inside_value) = o.get_key_value_mut();
+    ///         *inside_key = key_two.clone();
+    ///         *inside_value = 100;
+    ///     }
+    /// }
+    /// assert_eq!(map[&key_two], 100);
+    /// assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_key_value_mut(&mut self) -> (&mut K, &mut V) {
+        unsafe {
+            let &mut (ref mut key, ref mut value) = self.elem.as_mut();
+            (key, value)
+        }
+    }
+
+    /// Converts the OccupiedEntry into a mutable reference to the key and value in the entry
+    /// with a lifetime bound to the map itself.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    /// use std::rc::Rc;
+    ///
+    /// let key_one = Rc::new("a");
+    /// let key_two = Rc::new("a");
+    ///
+    /// let mut map: HashMap<Rc<&str>, u32> = HashMap::new();
+    /// map.insert(key_one.clone(), 10);
+    ///
+    /// assert_eq!(map[&key_one], 10);
+    /// assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);
+    ///
+    /// let inside_key: &mut Rc<&str>;
+    /// let inside_value: &mut u32;
+    /// match map.raw_entry_mut().from_key(&key_one) {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => {
+    ///         let tuple = o.into_key_value();
+    ///         inside_key = tuple.0;
+    ///         inside_value = tuple.1;
+    ///     }
+    /// }
+    /// *inside_key = key_two.clone();
+    /// *inside_value = 100;
+    /// assert_eq!(map[&key_two], 100);
+    /// assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_key_value(self) -> (&'a mut K, &'a mut V) {
+        unsafe {
+            let &mut (ref mut key, ref mut value) = self.elem.as_mut();
+            (key, value)
+        }
+    }
+
+    /// Sets the value of the entry, and returns the entry's old value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(mut o) => assert_eq!(o.insert(1000), 100),
+    /// }
+    ///
+    /// assert_eq!(map[&"a"], 1000);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(&mut self, value: V) -> V {
+        mem::replace(self.get_mut(), value)
+    }
+
+    /// Sets the value of the entry, and returns the entry's old value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    /// use std::rc::Rc;
+    ///
+    /// let key_one = Rc::new("a");
+    /// let key_two = Rc::new("a");
+    ///
+    /// let mut map: HashMap<Rc<&str>, u32> = HashMap::new();
+    /// map.insert(key_one.clone(), 10);
+    ///
+    /// assert_eq!(map[&key_one], 10);
+    /// assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);
+    ///
+    /// match map.raw_entry_mut().from_key(&key_one) {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(mut o) => {
+    ///         let old_key = o.insert_key(key_two.clone());
+    ///         assert!(Rc::ptr_eq(&old_key, &key_one));
+    ///     }
+    /// }
+    /// assert_eq!(map[&key_two], 10);
+    /// assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert_key(&mut self, key: K) -> K {
+        mem::replace(self.key_mut(), key)
+    }
+
+    /// Takes the value out of the entry, and returns it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => assert_eq!(o.remove(), 100),
+    /// }
+    /// assert_eq!(map.get(&"a"), None);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove(self) -> V {
+        self.remove_entry().1
+    }
+
+    /// Take the ownership of the key and value from the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => assert_eq!(o.remove_entry(), ("a", 100)),
+    /// }
+    /// assert_eq!(map.get(&"a"), None);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove_entry(self) -> (K, V) {
+        unsafe { self.table.remove(self.elem) }
+    }
+
+    /// Provides shared access to the key and owned access to the value of
+    /// the entry and allows to replace or remove it based on the
+    /// value of the returned option.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// let raw_entry = match map.raw_entry_mut().from_key(&"a") {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => o.replace_entry_with(|k, v| {
+    ///         assert_eq!(k, &"a");
+    ///         assert_eq!(v, 100);
+    ///         Some(v + 900)
+    ///     }),
+    /// };
+    /// let raw_entry = match raw_entry {
+    ///     RawEntryMut::Vacant(_) => panic!(),
+    ///     RawEntryMut::Occupied(o) => o.replace_entry_with(|k, v| {
+    ///         assert_eq!(k, &"a");
+    ///         assert_eq!(v, 1000);
+    ///         None
+    ///     }),
+    /// };
+    /// match raw_entry {
+    ///     RawEntryMut::Vacant(_) => { },
+    ///     RawEntryMut::Occupied(_) => panic!(),
+    /// };
+    /// assert_eq!(map.get(&"a"), None);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace_entry_with<F>(self, f: F) -> RawEntryMut<'a, K, V, S, A>
+    where
+        F: FnOnce(&K, V) -> Option<V>,
+    {
+        unsafe {
+            let still_occupied = self
+                .table
+                .replace_bucket_with(self.elem.clone(), |(key, value)| {
+                    f(&key, value).map(|new_value| (key, new_value))
+                });
+
+            if still_occupied {
+                RawEntryMut::Occupied(self)
+            } else {
+                RawEntryMut::Vacant(RawVacantEntryMut {
+                    table: self.table,
+                    hash_builder: self.hash_builder,
+                })
+            }
+        }
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> RawVacantEntryMut<'a, K, V, S, A> {
+    /// Sets the value of the entry with the VacantEntry's key,
+    /// and returns a mutable reference to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.raw_entry_mut().from_key(&"c") {
+    ///     RawEntryMut::Occupied(_) => panic!(),
+    ///     RawEntryMut::Vacant(v) => assert_eq!(v.insert("c", 300), (&mut "c", &mut 300)),
+    /// }
+    ///
+    /// assert_eq!(map[&"c"], 300);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self, key: K, value: V) -> (&'a mut K, &'a mut V)
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        let hash = make_insert_hash::<K, S>(self.hash_builder, &key);
+        self.insert_hashed_nocheck(hash, key, value)
+    }
+
+    /// Sets the value of the entry with the VacantEntry's key,
+    /// and returns a mutable reference to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
+    ///     use core::hash::Hasher;
+    ///     let mut state = hash_builder.build_hasher();
+    ///     key.hash(&mut state);
+    ///     state.finish()
+    /// }
+    ///
+    /// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
+    /// let key = "c";
+    /// let hash = compute_hash(map.hasher(), &key);
+    ///
+    /// match map.raw_entry_mut().from_key_hashed_nocheck(hash, &key) {
+    ///     RawEntryMut::Occupied(_) => panic!(),
+    ///     RawEntryMut::Vacant(v) => assert_eq!(
+    ///         v.insert_hashed_nocheck(hash, key, 300),
+    ///         (&mut "c", &mut 300)
+    ///     ),
+    /// }
+    ///
+    /// assert_eq!(map[&"c"], 300);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    #[allow(clippy::shadow_unrelated)]
+    pub fn insert_hashed_nocheck(self, hash: u64, key: K, value: V) -> (&'a mut K, &'a mut V)
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        let &mut (ref mut k, ref mut v) = self.table.insert_entry(
+            hash,
+            (key, value),
+            make_hasher::<K, _, V, S>(self.hash_builder),
+        );
+        (k, v)
+    }
+
+    /// Set the value of an entry with a custom hasher function.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use core::hash::{BuildHasher, Hash};
+    /// use hashbrown::hash_map::{HashMap, RawEntryMut};
+    ///
+    /// fn make_hasher<K, S>(hash_builder: &S) -> impl Fn(&K) -> u64 + '_
+    /// where
+    ///     K: Hash + ?Sized,
+    ///     S: BuildHasher,
+    /// {
+    ///     move |key: &K| {
+    ///         use core::hash::Hasher;
+    ///         let mut state = hash_builder.build_hasher();
+    ///         key.hash(&mut state);
+    ///         state.finish()
+    ///     }
+    /// }
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// let key = "a";
+    /// let hash_builder = map.hasher().clone();
+    /// let hash = make_hasher(&hash_builder)(&key);
+    ///
+    /// match map.raw_entry_mut().from_hash(hash, |q| q == &key) {
+    ///     RawEntryMut::Occupied(_) => panic!(),
+    ///     RawEntryMut::Vacant(v) => assert_eq!(
+    ///         v.insert_with_hasher(hash, key, 100, make_hasher(&hash_builder)),
+    ///         (&mut "a", &mut 100)
+    ///     ),
+    /// }
+    /// map.extend([("b", 200), ("c", 300), ("d", 400), ("e", 500), ("f", 600)]);
+    /// assert_eq!(map[&"a"], 100);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert_with_hasher<H>(
+        self,
+        hash: u64,
+        key: K,
+        value: V,
+        hasher: H,
+    ) -> (&'a mut K, &'a mut V)
+    where
+        H: Fn(&K) -> u64,
+    {
+        let &mut (ref mut k, ref mut v) = self
+            .table
+            .insert_entry(hash, (key, value), |x| hasher(&x.0));
+        (k, v)
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn insert_entry(self, key: K, value: V) -> RawOccupiedEntryMut<'a, K, V, S, A>
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        let hash = make_insert_hash::<K, S>(self.hash_builder, &key);
+        let elem = self.table.insert(
+            hash,
+            (key, value),
+            make_hasher::<K, _, V, S>(self.hash_builder),
+        );
+        RawOccupiedEntryMut {
+            elem,
+            table: self.table,
+            hash_builder: self.hash_builder,
+        }
+    }
+}
+
+impl<K, V, S, A: Allocator + Clone> Debug for RawEntryBuilderMut<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawEntryBuilder").finish()
+    }
+}
+
+impl<K: Debug, V: Debug, S, A: Allocator + Clone> Debug for RawEntryMut<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            RawEntryMut::Vacant(ref v) => f.debug_tuple("RawEntry").field(v).finish(),
+            RawEntryMut::Occupied(ref o) => f.debug_tuple("RawEntry").field(o).finish(),
+        }
+    }
+}
+
+impl<K: Debug, V: Debug, S, A: Allocator + Clone> Debug for RawOccupiedEntryMut<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawOccupiedEntryMut")
+            .field("key", self.key())
+            .field("value", self.get())
+            .finish()
+    }
+}
+
+impl<K, V, S, A: Allocator + Clone> Debug for RawVacantEntryMut<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawVacantEntryMut").finish()
+    }
+}
+
+impl<K, V, S, A: Allocator + Clone> Debug for RawEntryBuilder<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("RawEntryBuilder").finish()
+    }
+}
+
+/// A view into a single entry in a map, which may either be vacant or occupied.
+///
+/// This `enum` is constructed from the [`entry`] method on [`HashMap`].
+///
+/// [`HashMap`]: struct.HashMap.html
+/// [`entry`]: struct.HashMap.html#method.entry
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{Entry, HashMap, OccupiedEntry};
+///
+/// let mut map = HashMap::new();
+/// map.extend([("a", 10), ("b", 20), ("c", 30)]);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (insert)
+/// let entry: Entry<_, _, _> = map.entry("a");
+/// let _raw_o: OccupiedEntry<_, _, _> = entry.insert(1);
+/// assert_eq!(map.len(), 3);
+/// // Nonexistent key (insert)
+/// map.entry("d").insert(4);
+///
+/// // Existing key (or_insert)
+/// let v = map.entry("b").or_insert(2);
+/// assert_eq!(std::mem::replace(v, 2), 20);
+/// // Nonexistent key (or_insert)
+/// map.entry("e").or_insert(5);
+///
+/// // Existing key (or_insert_with)
+/// let v = map.entry("c").or_insert_with(|| 3);
+/// assert_eq!(std::mem::replace(v, 3), 30);
+/// // Nonexistent key (or_insert_with)
+/// map.entry("f").or_insert_with(|| 6);
+///
+/// println!("Our HashMap: {:?}", map);
+///
+/// let mut vec: Vec<_> = map.iter().map(|(&k, &v)| (k, v)).collect();
+/// // The `Iter` iterator produces items in arbitrary order, so the
+/// // items must be sorted to test them against a sorted array.
+/// vec.sort_unstable();
+/// assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3), ("d", 4), ("e", 5), ("f", 6)]);
+/// ```
+pub enum Entry<'a, K, V, S, A = Global>
+where
+    A: Allocator + Clone,
+{
+    /// An occupied entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{Entry, HashMap};
+    /// let mut map: HashMap<_, _> = [("a", 100), ("b", 200)].into();
+    ///
+    /// match map.entry("a") {
+    ///     Entry::Vacant(_) => unreachable!(),
+    ///     Entry::Occupied(_) => { }
+    /// }
+    /// ```
+    Occupied(OccupiedEntry<'a, K, V, S, A>),
+
+    /// A vacant entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{Entry, HashMap};
+    /// let mut map: HashMap<&str, i32> = HashMap::new();
+    ///
+    /// match map.entry("a") {
+    ///     Entry::Occupied(_) => unreachable!(),
+    ///     Entry::Vacant(_) => { }
+    /// }
+    /// ```
+    Vacant(VacantEntry<'a, K, V, S, A>),
+}
+
+impl<K: Debug, V: Debug, S, A: Allocator + Clone> Debug for Entry<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            Entry::Vacant(ref v) => f.debug_tuple("Entry").field(v).finish(),
+            Entry::Occupied(ref o) => f.debug_tuple("Entry").field(o).finish(),
+        }
+    }
+}
+
+/// A view into an occupied entry in a `HashMap`.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{Entry, HashMap, OccupiedEntry};
+///
+/// let mut map = HashMap::new();
+/// map.extend([("a", 10), ("b", 20), ("c", 30)]);
+///
+/// let _entry_o: OccupiedEntry<_, _, _> = map.entry("a").insert(100);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (insert and update)
+/// match map.entry("a") {
+///     Entry::Vacant(_) => unreachable!(),
+///     Entry::Occupied(mut view) => {
+///         assert_eq!(view.get(), &100);
+///         let v = view.get_mut();
+///         *v *= 10;
+///         assert_eq!(view.insert(1111), 1000);
+///     }
+/// }
+///
+/// assert_eq!(map[&"a"], 1111);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (take)
+/// match map.entry("c") {
+///     Entry::Vacant(_) => unreachable!(),
+///     Entry::Occupied(view) => {
+///         assert_eq!(view.remove_entry(), ("c", 30));
+///     }
+/// }
+/// assert_eq!(map.get(&"c"), None);
+/// assert_eq!(map.len(), 2);
+/// ```
+pub struct OccupiedEntry<'a, K, V, S, A: Allocator + Clone = Global> {
+    hash: u64,
+    key: Option<K>,
+    elem: Bucket<(K, V)>,
+    table: &'a mut HashMap<K, V, S, A>,
+}
+
+unsafe impl<K, V, S, A> Send for OccupiedEntry<'_, K, V, S, A>
+where
+    K: Send,
+    V: Send,
+    S: Send,
+    A: Send + Allocator + Clone,
+{
+}
+unsafe impl<K, V, S, A> Sync for OccupiedEntry<'_, K, V, S, A>
+where
+    K: Sync,
+    V: Sync,
+    S: Sync,
+    A: Sync + Allocator + Clone,
+{
+}
+
+impl<K: Debug, V: Debug, S, A: Allocator + Clone> Debug for OccupiedEntry<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OccupiedEntry")
+            .field("key", self.key())
+            .field("value", self.get())
+            .finish()
+    }
+}
+
+/// A view into a vacant entry in a `HashMap`.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{Entry, HashMap, VacantEntry};
+///
+/// let mut map = HashMap::<&str, i32>::new();
+///
+/// let entry_v: VacantEntry<_, _, _> = match map.entry("a") {
+///     Entry::Vacant(view) => view,
+///     Entry::Occupied(_) => unreachable!(),
+/// };
+/// entry_v.insert(10);
+/// assert!(map[&"a"] == 10 && map.len() == 1);
+///
+/// // Nonexistent key (insert and update)
+/// match map.entry("b") {
+///     Entry::Occupied(_) => unreachable!(),
+///     Entry::Vacant(view) => {
+///         let value = view.insert(2);
+///         assert_eq!(*value, 2);
+///         *value = 20;
+///     }
+/// }
+/// assert!(map[&"b"] == 20 && map.len() == 2);
+/// ```
+pub struct VacantEntry<'a, K, V, S, A: Allocator + Clone = Global> {
+    hash: u64,
+    key: K,
+    table: &'a mut HashMap<K, V, S, A>,
+}
+
+impl<K: Debug, V, S, A: Allocator + Clone> Debug for VacantEntry<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("VacantEntry").field(self.key()).finish()
+    }
+}
+
+/// A view into a single entry in a map, which may either be vacant or occupied,
+/// with any borrowed form of the map's key type.
+///
+///
+/// This `enum` is constructed from the [`entry_ref`] method on [`HashMap`].
+///
+/// [`Hash`] and [`Eq`] on the borrowed form of the map's key type *must* match those
+/// for the key type. It also require that key may be constructed from the borrowed
+/// form through the [`From`] trait.
+///
+/// [`HashMap`]: struct.HashMap.html
+/// [`entry_ref`]: struct.HashMap.html#method.entry_ref
+/// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+/// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+/// [`From`]: https://doc.rust-lang.org/std/convert/trait.From.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{EntryRef, HashMap, OccupiedEntryRef};
+///
+/// let mut map = HashMap::new();
+/// map.extend([("a".to_owned(), 10), ("b".into(), 20), ("c".into(), 30)]);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (insert)
+/// let key = String::from("a");
+/// let entry: EntryRef<_, _, _, _> = map.entry_ref(&key);
+/// let _raw_o: OccupiedEntryRef<_, _, _, _> = entry.insert(1);
+/// assert_eq!(map.len(), 3);
+/// // Nonexistent key (insert)
+/// map.entry_ref("d").insert(4);
+///
+/// // Existing key (or_insert)
+/// let v = map.entry_ref("b").or_insert(2);
+/// assert_eq!(std::mem::replace(v, 2), 20);
+/// // Nonexistent key (or_insert)
+/// map.entry_ref("e").or_insert(5);
+///
+/// // Existing key (or_insert_with)
+/// let v = map.entry_ref("c").or_insert_with(|| 3);
+/// assert_eq!(std::mem::replace(v, 3), 30);
+/// // Nonexistent key (or_insert_with)
+/// map.entry_ref("f").or_insert_with(|| 6);
+///
+/// println!("Our HashMap: {:?}", map);
+///
+/// for (key, value) in ["a", "b", "c", "d", "e", "f"].into_iter().zip(1..=6) {
+///     assert_eq!(map[key], value)
+/// }
+/// assert_eq!(map.len(), 6);
+/// ```
+pub enum EntryRef<'a, 'b, K, Q: ?Sized, V, S, A = Global>
+where
+    A: Allocator + Clone,
+{
+    /// An occupied entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{EntryRef, HashMap};
+    /// let mut map: HashMap<_, _> = [("a".to_owned(), 100), ("b".into(), 200)].into();
+    ///
+    /// match map.entry_ref("a") {
+    ///     EntryRef::Vacant(_) => unreachable!(),
+    ///     EntryRef::Occupied(_) => { }
+    /// }
+    /// ```
+    Occupied(OccupiedEntryRef<'a, 'b, K, Q, V, S, A>),
+
+    /// A vacant entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{EntryRef, HashMap};
+    /// let mut map: HashMap<String, i32> = HashMap::new();
+    ///
+    /// match map.entry_ref("a") {
+    ///     EntryRef::Occupied(_) => unreachable!(),
+    ///     EntryRef::Vacant(_) => { }
+    /// }
+    /// ```
+    Vacant(VacantEntryRef<'a, 'b, K, Q, V, S, A>),
+}
+
+impl<K: Borrow<Q>, Q: ?Sized + Debug, V: Debug, S, A: Allocator + Clone> Debug
+    for EntryRef<'_, '_, K, Q, V, S, A>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match *self {
+            EntryRef::Vacant(ref v) => f.debug_tuple("EntryRef").field(v).finish(),
+            EntryRef::Occupied(ref o) => f.debug_tuple("EntryRef").field(o).finish(),
+        }
+    }
+}
+
+enum KeyOrRef<'a, K, Q: ?Sized> {
+    Borrowed(&'a Q),
+    Owned(K),
+}
+
+impl<'a, K, Q: ?Sized> KeyOrRef<'a, K, Q> {
+    fn into_owned(self) -> K
+    where
+        K: From<&'a Q>,
+    {
+        match self {
+            Self::Borrowed(borrowed) => borrowed.into(),
+            Self::Owned(owned) => owned,
+        }
+    }
+}
+
+impl<'a, K: Borrow<Q>, Q: ?Sized> AsRef<Q> for KeyOrRef<'a, K, Q> {
+    fn as_ref(&self) -> &Q {
+        match self {
+            Self::Borrowed(borrowed) => borrowed,
+            Self::Owned(owned) => owned.borrow(),
+        }
+    }
+}
+
+/// A view into an occupied entry in a `HashMap`.
+/// It is part of the [`EntryRef`] enum.
+///
+/// [`EntryRef`]: enum.EntryRef.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{EntryRef, HashMap, OccupiedEntryRef};
+///
+/// let mut map = HashMap::new();
+/// map.extend([("a".to_owned(), 10), ("b".into(), 20), ("c".into(), 30)]);
+///
+/// let key = String::from("a");
+/// let _entry_o: OccupiedEntryRef<_, _, _, _> = map.entry_ref(&key).insert(100);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (insert and update)
+/// match map.entry_ref("a") {
+///     EntryRef::Vacant(_) => unreachable!(),
+///     EntryRef::Occupied(mut view) => {
+///         assert_eq!(view.get(), &100);
+///         let v = view.get_mut();
+///         *v *= 10;
+///         assert_eq!(view.insert(1111), 1000);
+///     }
+/// }
+///
+/// assert_eq!(map["a"], 1111);
+/// assert_eq!(map.len(), 3);
+///
+/// // Existing key (take)
+/// match map.entry_ref("c") {
+///     EntryRef::Vacant(_) => unreachable!(),
+///     EntryRef::Occupied(view) => {
+///         assert_eq!(view.remove_entry(), ("c".to_owned(), 30));
+///     }
+/// }
+/// assert_eq!(map.get("c"), None);
+/// assert_eq!(map.len(), 2);
+/// ```
+pub struct OccupiedEntryRef<'a, 'b, K, Q: ?Sized, V, S, A: Allocator + Clone = Global> {
+    hash: u64,
+    key: Option<KeyOrRef<'b, K, Q>>,
+    elem: Bucket<(K, V)>,
+    table: &'a mut HashMap<K, V, S, A>,
+}
+
+unsafe impl<'a, 'b, K, Q, V, S, A> Send for OccupiedEntryRef<'a, 'b, K, Q, V, S, A>
+where
+    K: Send,
+    Q: Sync + ?Sized,
+    V: Send,
+    S: Send,
+    A: Send + Allocator + Clone,
+{
+}
+unsafe impl<'a, 'b, K, Q, V, S, A> Sync for OccupiedEntryRef<'a, 'b, K, Q, V, S, A>
+where
+    K: Sync,
+    Q: Sync + ?Sized,
+    V: Sync,
+    S: Sync,
+    A: Sync + Allocator + Clone,
+{
+}
+
+impl<K: Borrow<Q>, Q: ?Sized + Debug, V: Debug, S, A: Allocator + Clone> Debug
+    for OccupiedEntryRef<'_, '_, K, Q, V, S, A>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OccupiedEntryRef")
+            .field("key", &self.key())
+            .field("value", &self.get())
+            .finish()
+    }
+}
+
+/// A view into a vacant entry in a `HashMap`.
+/// It is part of the [`EntryRef`] enum.
+///
+/// [`EntryRef`]: enum.EntryRef.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{EntryRef, HashMap, VacantEntryRef};
+///
+/// let mut map = HashMap::<String, i32>::new();
+///
+/// let entry_v: VacantEntryRef<_, _, _, _> = match map.entry_ref("a") {
+///     EntryRef::Vacant(view) => view,
+///     EntryRef::Occupied(_) => unreachable!(),
+/// };
+/// entry_v.insert(10);
+/// assert!(map["a"] == 10 && map.len() == 1);
+///
+/// // Nonexistent key (insert and update)
+/// match map.entry_ref("b") {
+///     EntryRef::Occupied(_) => unreachable!(),
+///     EntryRef::Vacant(view) => {
+///         let value = view.insert(2);
+///         assert_eq!(*value, 2);
+///         *value = 20;
+///     }
+/// }
+/// assert!(map["b"] == 20 && map.len() == 2);
+/// ```
+pub struct VacantEntryRef<'a, 'b, K, Q: ?Sized, V, S, A: Allocator + Clone = Global> {
+    hash: u64,
+    key: KeyOrRef<'b, K, Q>,
+    table: &'a mut HashMap<K, V, S, A>,
+}
+
+impl<K: Borrow<Q>, Q: ?Sized + Debug, V, S, A: Allocator + Clone> Debug
+    for VacantEntryRef<'_, '_, K, Q, V, S, A>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("VacantEntryRef").field(&self.key()).finish()
+    }
+}
+
+/// The error returned by [`try_insert`](HashMap::try_insert) when the key already exists.
+///
+/// Contains the occupied entry, and the value that was not inserted.
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_map::{HashMap, OccupiedError};
+///
+/// let mut map: HashMap<_, _> = [("a", 10), ("b", 20)].into();
+///
+/// // try_insert method returns mutable reference to the value if keys are vacant,
+/// // but if the map did have key present, nothing is updated, and the provided
+/// // value is returned inside `Err(_)` variant
+/// match map.try_insert("a", 100) {
+///     Err(OccupiedError { mut entry, value }) => {
+///         assert_eq!(entry.key(), &"a");
+///         assert_eq!(value, 100);
+///         assert_eq!(entry.insert(100), 10)
+///     }
+///     _ => unreachable!(),
+/// }
+/// assert_eq!(map[&"a"], 100);
+/// ```
+pub struct OccupiedError<'a, K, V, S, A: Allocator + Clone = Global> {
+    /// The entry in the map that was already occupied.
+    pub entry: OccupiedEntry<'a, K, V, S, A>,
+    /// The value which was not inserted, because the entry was already occupied.
+    pub value: V,
+}
+
+impl<K: Debug, V: Debug, S, A: Allocator + Clone> Debug for OccupiedError<'_, K, V, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OccupiedError")
+            .field("key", self.entry.key())
+            .field("old_value", self.entry.get())
+            .field("new_value", &self.value)
+            .finish()
+    }
+}
+
+impl<'a, K: Debug, V: Debug, S, A: Allocator + Clone> fmt::Display
+    for OccupiedError<'a, K, V, S, A>
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "failed to insert {:?}, key {:?} already exists with value {:?}",
+            self.value,
+            self.entry.key(),
+            self.entry.get(),
+        )
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> IntoIterator for &'a HashMap<K, V, S, A> {
+    type Item = (&'a K, &'a V);
+    type IntoIter = Iter<'a, K, V>;
+
+    /// Creates an iterator over the entries of a `HashMap` in arbitrary order.
+    /// The iterator element type is `(&'a K, &'a V)`.
+    ///
+    /// Return the same `Iter` struct as by the [`iter`] method on [`HashMap`].
+    ///
+    /// [`iter`]: struct.HashMap.html#method.iter
+    /// [`HashMap`]: struct.HashMap.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// let map_one: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
+    /// let mut map_two = HashMap::new();
+    ///
+    /// for (key, value) in &map_one {
+    ///     println!("Key: {}, Value: {}", key, value);
+    ///     map_two.insert_unique_unchecked(*key, *value);
+    /// }
+    ///
+    /// assert_eq!(map_one, map_two);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn into_iter(self) -> Iter<'a, K, V> {
+        self.iter()
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> IntoIterator for &'a mut HashMap<K, V, S, A> {
+    type Item = (&'a K, &'a mut V);
+    type IntoIter = IterMut<'a, K, V>;
+
+    /// Creates an iterator over the entries of a `HashMap` in arbitrary order
+    /// with mutable references to the values. The iterator element type is
+    /// `(&'a K, &'a mut V)`.
+    ///
+    /// Return the same `IterMut` struct as by the [`iter_mut`] method on
+    /// [`HashMap`].
+    ///
+    /// [`iter_mut`]: struct.HashMap.html#method.iter_mut
+    /// [`HashMap`]: struct.HashMap.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// let mut map: HashMap<_, _> = [("a", 1), ("b", 2), ("c", 3)].into();
+    ///
+    /// for (key, value) in &mut map {
+    ///     println!("Key: {}, Value: {}", key, value);
+    ///     *value *= 2;
+    /// }
+    ///
+    /// let mut vec = map.iter().collect::<Vec<_>>();
+    /// // The `Iter` iterator produces items in arbitrary order, so the
+    /// // items must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [(&"a", &2), (&"b", &4), (&"c", &6)]);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn into_iter(self) -> IterMut<'a, K, V> {
+        self.iter_mut()
+    }
+}
+
+impl<K, V, S, A: Allocator + Clone> IntoIterator for HashMap<K, V, S, A> {
+    type Item = (K, V);
+    type IntoIter = IntoIter<K, V, A>;
+
+    /// Creates a consuming iterator, that is, one that moves each key-value
+    /// pair out of the map in arbitrary order. The map cannot be used after
+    /// calling this.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let map: HashMap<_, _> = [("a", 1), ("b", 2), ("c", 3)].into();
+    ///
+    /// // Not possible with .iter()
+    /// let mut vec: Vec<(&str, i32)> = map.into_iter().collect();
+    /// // The `IntoIter` iterator produces items in arbitrary order, so
+    /// // the items must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3)]);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn into_iter(self) -> IntoIter<K, V, A> {
+        IntoIter {
+            inner: self.table.into_iter(),
+        }
+    }
+}
+
+impl<'a, K, V> Iterator for Iter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<(&'a K, &'a V)> {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.inner.next() {
+            Some(x) => unsafe {
+                let r = x.as_ref();
+                Some((&r.0, &r.1))
+            },
+            None => None,
+        }
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<K, V> FusedIterator for Iter<'_, K, V> {}
+
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.inner.next() {
+            Some(x) => unsafe {
+                let r = x.as_mut();
+                Some((&r.0, &mut r.1))
+            },
+            None => None,
+        }
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+impl<K, V> FusedIterator for IterMut<'_, K, V> {}
+
+impl<K, V> fmt::Debug for IterMut<'_, K, V>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+impl<K, V, A: Allocator + Clone> Iterator for IntoIter<K, V, A> {
+    type Item = (K, V);
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<(K, V)> {
+        self.inner.next()
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+impl<K, V, A: Allocator + Clone> ExactSizeIterator for IntoIter<K, V, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+impl<K, V, A: Allocator + Clone> FusedIterator for IntoIter<K, V, A> {}
+
+impl<K: Debug, V: Debug, A: Allocator + Clone> fmt::Debug for IntoIter<K, V, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+impl<'a, K, V> Iterator for Keys<'a, K, V> {
+    type Item = &'a K;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a K> {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.inner.next() {
+            Some((k, _)) => Some(k),
+            None => None,
+        }
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+impl<K, V> FusedIterator for Keys<'_, K, V> {}
+
+impl<'a, K, V> Iterator for Values<'a, K, V> {
+    type Item = &'a V;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a V> {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.inner.next() {
+            Some((_, v)) => Some(v),
+            None => None,
+        }
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+impl<K, V> ExactSizeIterator for Values<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+impl<K, V> FusedIterator for Values<'_, K, V> {}
+
+impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
+    type Item = &'a mut V;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a mut V> {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.inner.next() {
+            Some((_, v)) => Some(v),
+            None => None,
+        }
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
+
+impl<K, V: Debug> fmt::Debug for ValuesMut<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list()
+            .entries(self.inner.iter().map(|(_, val)| val))
+            .finish()
+    }
+}
+
+impl<'a, K, V, A: Allocator + Clone> Iterator for Drain<'a, K, V, A> {
+    type Item = (K, V);
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<(K, V)> {
+        self.inner.next()
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.inner.size_hint()
+    }
+}
+impl<K, V, A: Allocator + Clone> ExactSizeIterator for Drain<'_, K, V, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+impl<K, V, A: Allocator + Clone> FusedIterator for Drain<'_, K, V, A> {}
+
+impl<K, V, A> fmt::Debug for Drain<'_, K, V, A>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+    A: Allocator + Clone,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.iter()).finish()
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> Entry<'a, K, V, S, A> {
+    /// Sets the value of the entry, and returns an OccupiedEntry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// let entry = map.entry("horseyland").insert(37);
+    ///
+    /// assert_eq!(entry.key(), &"horseyland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self, value: V) -> OccupiedEntry<'a, K, V, S, A>
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(mut entry) => {
+                entry.insert(value);
+                entry
+            }
+            Entry::Vacant(entry) => entry.insert_entry(value),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the default if empty, and returns
+    /// a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry("poneyland").or_insert(3);
+    /// assert_eq!(map["poneyland"], 3);
+    ///
+    /// // existing key
+    /// *map.entry("poneyland").or_insert(10) *= 2;
+    /// assert_eq!(map["poneyland"], 6);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert(self, default: V) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => entry.insert(default),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the result of the default function if empty,
+    /// and returns a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry("poneyland").or_insert_with(|| 3);
+    /// assert_eq!(map["poneyland"], 3);
+    ///
+    /// // existing key
+    /// *map.entry("poneyland").or_insert_with(|| 10) *= 2;
+    /// assert_eq!(map["poneyland"], 6);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => entry.insert(default()),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting, if empty, the result of the default function.
+    /// This method allows for generating key-derived values for insertion by providing the default
+    /// function a reference to the key that was moved during the `.entry(key)` method call.
+    ///
+    /// The reference to the moved key is provided so that cloning or copying the key is
+    /// unnecessary, unlike with `.or_insert_with(|| ... )`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, usize> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry("poneyland").or_insert_with_key(|key| key.chars().count());
+    /// assert_eq!(map["poneyland"], 9);
+    ///
+    /// // existing key
+    /// *map.entry("poneyland").or_insert_with_key(|key| key.chars().count() * 10) *= 2;
+    /// assert_eq!(map["poneyland"], 18);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert_with_key<F: FnOnce(&K) -> V>(self, default: F) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => {
+                let value = default(entry.key());
+                entry.insert(value)
+            }
+        }
+    }
+
+    /// Returns a reference to this entry's key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(3);
+    /// // existing key
+    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
+    /// // nonexistent key
+    /// assert_eq!(map.entry("horseland").key(), &"horseland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key(&self) -> &K {
+        match *self {
+            Entry::Occupied(ref entry) => entry.key(),
+            Entry::Vacant(ref entry) => entry.key(),
+        }
+    }
+
+    /// Provides in-place mutable access to an occupied entry before any
+    /// potential inserts into the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// map.entry("poneyland")
+    ///    .and_modify(|e| { *e += 1 })
+    ///    .or_insert(42);
+    /// assert_eq!(map["poneyland"], 42);
+    ///
+    /// map.entry("poneyland")
+    ///    .and_modify(|e| { *e += 1 })
+    ///    .or_insert(42);
+    /// assert_eq!(map["poneyland"], 43);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn and_modify<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&mut V),
+    {
+        match self {
+            Entry::Occupied(mut entry) => {
+                f(entry.get_mut());
+                Entry::Occupied(entry)
+            }
+            Entry::Vacant(entry) => Entry::Vacant(entry),
+        }
+    }
+
+    /// Provides shared access to the key and owned access to the value of
+    /// an occupied entry and allows to replace or remove it based on the
+    /// value of the returned option.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// let entry = map
+    ///     .entry("poneyland")
+    ///     .and_replace_entry_with(|_k, _v| panic!());
+    ///
+    /// match entry {
+    ///     Entry::Vacant(e) => {
+    ///         assert_eq!(e.key(), &"poneyland");
+    ///     }
+    ///     Entry::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// map.insert("poneyland", 42);
+    ///
+    /// let entry = map
+    ///     .entry("poneyland")
+    ///     .and_replace_entry_with(|k, v| {
+    ///         assert_eq!(k, &"poneyland");
+    ///         assert_eq!(v, 42);
+    ///         Some(v + 1)
+    ///     });
+    ///
+    /// match entry {
+    ///     Entry::Occupied(e) => {
+    ///         assert_eq!(e.key(), &"poneyland");
+    ///         assert_eq!(e.get(), &43);
+    ///     }
+    ///     Entry::Vacant(_) => panic!(),
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 43);
+    ///
+    /// let entry = map
+    ///     .entry("poneyland")
+    ///     .and_replace_entry_with(|_k, _v| None);
+    ///
+    /// match entry {
+    ///     Entry::Vacant(e) => assert_eq!(e.key(), &"poneyland"),
+    ///     Entry::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// assert!(!map.contains_key("poneyland"));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn and_replace_entry_with<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&K, V) -> Option<V>,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.replace_entry_with(f),
+            Entry::Vacant(_) => self,
+        }
+    }
+}
+
+impl<'a, K, V: Default, S, A: Allocator + Clone> Entry<'a, K, V, S, A> {
+    /// Ensures a value is in the entry by inserting the default value if empty,
+    /// and returns a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, Option<u32>> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry("poneyland").or_default();
+    /// assert_eq!(map["poneyland"], None);
+    ///
+    /// map.insert("horseland", Some(3));
+    ///
+    /// // existing key
+    /// assert_eq!(map.entry("horseland").or_default(), &mut Some(3));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_default(self) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(entry) => entry.into_mut(),
+            Entry::Vacant(entry) => entry.insert(Default::default()),
+        }
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> OccupiedEntry<'a, K, V, S, A> {
+    /// Gets a reference to the key in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{Entry, HashMap};
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// match map.entry("poneyland") {
+    ///     Entry::Vacant(_) => panic!(),
+    ///     Entry::Occupied(entry) => assert_eq!(entry.key(), &"poneyland"),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key(&self) -> &K {
+        unsafe { &self.elem.as_ref().0 }
+    }
+
+    /// Take the ownership of the key and value from the map.
+    /// Keeps the allocated memory for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// // The map is empty
+    /// assert!(map.is_empty() && map.capacity() == 0);
+    ///
+    /// map.entry("poneyland").or_insert(12);
+    /// let capacity_before_remove = map.capacity();
+    ///
+    /// if let Entry::Occupied(o) = map.entry("poneyland") {
+    ///     // We delete the entry from the map.
+    ///     assert_eq!(o.remove_entry(), ("poneyland", 12));
+    /// }
+    ///
+    /// assert_eq!(map.contains_key("poneyland"), false);
+    /// // Now map hold none elements but capacity is equal to the old one
+    /// assert!(map.len() == 0 && map.capacity() == capacity_before_remove);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove_entry(self) -> (K, V) {
+        unsafe { self.table.table.remove(self.elem) }
+    }
+
+    /// Gets a reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// match map.entry("poneyland") {
+    ///     Entry::Vacant(_) => panic!(),
+    ///     Entry::Occupied(entry) => assert_eq!(entry.get(), &12),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get(&self) -> &V {
+        unsafe { &self.elem.as_ref().1 }
+    }
+
+    /// Gets a mutable reference to the value in the entry.
+    ///
+    /// If you need a reference to the `OccupiedEntry` which may outlive the
+    /// destruction of the `Entry` value, see [`into_mut`].
+    ///
+    /// [`into_mut`]: #method.into_mut
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// assert_eq!(map["poneyland"], 12);
+    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
+    ///     *o.get_mut() += 10;
+    ///     assert_eq!(*o.get(), 22);
+    ///
+    ///     // We can use the same Entry multiple times.
+    ///     *o.get_mut() += 2;
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 24);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_mut(&mut self) -> &mut V {
+        unsafe { &mut self.elem.as_mut().1 }
+    }
+
+    /// Converts the OccupiedEntry into a mutable reference to the value in the entry
+    /// with a lifetime bound to the map itself.
+    ///
+    /// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
+    ///
+    /// [`get_mut`]: #method.get_mut
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{Entry, HashMap};
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// assert_eq!(map["poneyland"], 12);
+    ///
+    /// let value: &mut u32;
+    /// match map.entry("poneyland") {
+    ///     Entry::Occupied(entry) => value = entry.into_mut(),
+    ///     Entry::Vacant(_) => panic!(),
+    /// }
+    /// *value += 10;
+    ///
+    /// assert_eq!(map["poneyland"], 22);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_mut(self) -> &'a mut V {
+        unsafe { &mut self.elem.as_mut().1 }
+    }
+
+    /// Sets the value of the entry, and returns the entry's old value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.entry("poneyland").or_insert(12);
+    ///
+    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
+    ///     assert_eq!(o.insert(15), 12);
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 15);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(&mut self, value: V) -> V {
+        mem::replace(self.get_mut(), value)
+    }
+
+    /// Takes the value out of the entry, and returns it.
+    /// Keeps the allocated memory for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// // The map is empty
+    /// assert!(map.is_empty() && map.capacity() == 0);
+    ///
+    /// map.entry("poneyland").or_insert(12);
+    /// let capacity_before_remove = map.capacity();
+    ///
+    /// if let Entry::Occupied(o) = map.entry("poneyland") {
+    ///     assert_eq!(o.remove(), 12);
+    /// }
+    ///
+    /// assert_eq!(map.contains_key("poneyland"), false);
+    /// // Now map hold none elements but capacity is equal to the old one
+    /// assert!(map.len() == 0 && map.capacity() == capacity_before_remove);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove(self) -> V {
+        self.remove_entry().1
+    }
+
+    /// Replaces the entry, returning the old key and value. The new key in the hash map will be
+    /// the key used to create this entry.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if this OccupiedEntry was created through [`Entry::insert`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    ///  use hashbrown::hash_map::{Entry, HashMap};
+    ///  use std::rc::Rc;
+    ///
+    ///  let mut map: HashMap<Rc<String>, u32> = HashMap::new();
+    ///  let key_one = Rc::new("Stringthing".to_string());
+    ///  let key_two = Rc::new("Stringthing".to_string());
+    ///
+    ///  map.insert(key_one.clone(), 15);
+    ///  assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);
+    ///
+    ///  match map.entry(key_two.clone()) {
+    ///      Entry::Occupied(entry) => {
+    ///          let (old_key, old_value): (Rc<String>, u32) = entry.replace_entry(16);
+    ///          assert!(Rc::ptr_eq(&key_one, &old_key) && old_value == 15);
+    ///      }
+    ///      Entry::Vacant(_) => panic!(),
+    ///  }
+    ///
+    ///  assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
+    ///  assert_eq!(map[&"Stringthing".to_owned()], 16);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace_entry(self, value: V) -> (K, V) {
+        let entry = unsafe { self.elem.as_mut() };
+
+        let old_key = mem::replace(&mut entry.0, self.key.unwrap());
+        let old_value = mem::replace(&mut entry.1, value);
+
+        (old_key, old_value)
+    }
+
+    /// Replaces the key in the hash map with the key used to create this entry.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if this OccupiedEntry was created through [`Entry::insert`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{Entry, HashMap};
+    /// use std::rc::Rc;
+    ///
+    /// let mut map: HashMap<Rc<String>, usize> = HashMap::with_capacity(6);
+    /// let mut keys_one: Vec<Rc<String>> = Vec::with_capacity(6);
+    /// let mut keys_two: Vec<Rc<String>> = Vec::with_capacity(6);
+    ///
+    /// for (value, key) in ["a", "b", "c", "d", "e", "f"].into_iter().enumerate() {
+    ///     let rc_key = Rc::new(key.to_owned());
+    ///     keys_one.push(rc_key.clone());
+    ///     map.insert(rc_key.clone(), value);
+    ///     keys_two.push(Rc::new(key.to_owned()));
+    /// }
+    ///
+    /// assert!(
+    ///     keys_one.iter().all(|key| Rc::strong_count(key) == 2)
+    ///         && keys_two.iter().all(|key| Rc::strong_count(key) == 1)
+    /// );
+    ///
+    /// reclaim_memory(&mut map, &keys_two);
+    ///
+    /// assert!(
+    ///     keys_one.iter().all(|key| Rc::strong_count(key) == 1)
+    ///         && keys_two.iter().all(|key| Rc::strong_count(key) == 2)
+    /// );
+    ///
+    /// fn reclaim_memory(map: &mut HashMap<Rc<String>, usize>, keys: &[Rc<String>]) {
+    ///     for key in keys {
+    ///         if let Entry::Occupied(entry) = map.entry(key.clone()) {
+    ///         // Replaces the entry's key with our version of it in `keys`.
+    ///             entry.replace_key();
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace_key(self) -> K {
+        let entry = unsafe { self.elem.as_mut() };
+        mem::replace(&mut entry.0, self.key.unwrap())
+    }
+
+    /// Provides shared access to the key and owned access to the value of
+    /// the entry and allows to replace or remove it based on the
+    /// value of the returned option.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// map.insert("poneyland", 42);
+    ///
+    /// let entry = match map.entry("poneyland") {
+    ///     Entry::Occupied(e) => {
+    ///         e.replace_entry_with(|k, v| {
+    ///             assert_eq!(k, &"poneyland");
+    ///             assert_eq!(v, 42);
+    ///             Some(v + 1)
+    ///         })
+    ///     }
+    ///     Entry::Vacant(_) => panic!(),
+    /// };
+    ///
+    /// match entry {
+    ///     Entry::Occupied(e) => {
+    ///         assert_eq!(e.key(), &"poneyland");
+    ///         assert_eq!(e.get(), &43);
+    ///     }
+    ///     Entry::Vacant(_) => panic!(),
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 43);
+    ///
+    /// let entry = match map.entry("poneyland") {
+    ///     Entry::Occupied(e) => e.replace_entry_with(|_k, _v| None),
+    ///     Entry::Vacant(_) => panic!(),
+    /// };
+    ///
+    /// match entry {
+    ///     Entry::Vacant(e) => {
+    ///         assert_eq!(e.key(), &"poneyland");
+    ///     }
+    ///     Entry::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// assert!(!map.contains_key("poneyland"));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace_entry_with<F>(self, f: F) -> Entry<'a, K, V, S, A>
+    where
+        F: FnOnce(&K, V) -> Option<V>,
+    {
+        unsafe {
+            let mut spare_key = None;
+
+            self.table
+                .table
+                .replace_bucket_with(self.elem.clone(), |(key, value)| {
+                    if let Some(new_value) = f(&key, value) {
+                        Some((key, new_value))
+                    } else {
+                        spare_key = Some(key);
+                        None
+                    }
+                });
+
+            if let Some(key) = spare_key {
+                Entry::Vacant(VacantEntry {
+                    hash: self.hash,
+                    key,
+                    table: self.table,
+                })
+            } else {
+                Entry::Occupied(self)
+            }
+        }
+    }
+}
+
+impl<'a, K, V, S, A: Allocator + Clone> VacantEntry<'a, K, V, S, A> {
+    /// Gets a reference to the key that would be used when inserting a value
+    /// through the `VacantEntry`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key(&self) -> &K {
+        &self.key
+    }
+
+    /// Take ownership of the key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{Entry, HashMap};
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// match map.entry("poneyland") {
+    ///     Entry::Occupied(_) => panic!(),
+    ///     Entry::Vacant(v) => assert_eq!(v.into_key(), "poneyland"),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_key(self) -> K {
+        self.key
+    }
+
+    /// Sets the value of the entry with the VacantEntry's key,
+    /// and returns a mutable reference to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::Entry;
+    ///
+    /// let mut map: HashMap<&str, u32> = HashMap::new();
+    ///
+    /// if let Entry::Vacant(o) = map.entry("poneyland") {
+    ///     o.insert(37);
+    /// }
+    /// assert_eq!(map["poneyland"], 37);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self, value: V) -> &'a mut V
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        let table = &mut self.table.table;
+        let entry = table.insert_entry(
+            self.hash,
+            (self.key, value),
+            make_hasher::<K, _, V, S>(&self.table.hash_builder),
+        );
+        &mut entry.1
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub(crate) fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V, S, A>
+    where
+        K: Hash,
+        S: BuildHasher,
+    {
+        let elem = self.table.table.insert(
+            self.hash,
+            (self.key, value),
+            make_hasher::<K, _, V, S>(&self.table.hash_builder),
+        );
+        OccupiedEntry {
+            hash: self.hash,
+            key: None,
+            elem,
+            table: self.table,
+        }
+    }
+}
+
+impl<'a, 'b, K, Q: ?Sized, V, S, A: Allocator + Clone> EntryRef<'a, 'b, K, Q, V, S, A> {
+    /// Sets the value of the entry, and returns an OccupiedEntryRef.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// let entry = map.entry_ref("horseyland").insert(37);
+    ///
+    /// assert_eq!(entry.key(), "horseyland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self, value: V) -> OccupiedEntryRef<'a, 'b, K, Q, V, S, A>
+    where
+        K: Hash + From<&'b Q>,
+        S: BuildHasher,
+    {
+        match self {
+            EntryRef::Occupied(mut entry) => {
+                entry.insert(value);
+                entry
+            }
+            EntryRef::Vacant(entry) => entry.insert_entry(value),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the default if empty, and returns
+    /// a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry_ref("poneyland").or_insert(3);
+    /// assert_eq!(map["poneyland"], 3);
+    ///
+    /// // existing key
+    /// *map.entry_ref("poneyland").or_insert(10) *= 2;
+    /// assert_eq!(map["poneyland"], 6);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert(self, default: V) -> &'a mut V
+    where
+        K: Hash + From<&'b Q>,
+        S: BuildHasher,
+    {
+        match self {
+            EntryRef::Occupied(entry) => entry.into_mut(),
+            EntryRef::Vacant(entry) => entry.insert(default),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the result of the default function if empty,
+    /// and returns a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry_ref("poneyland").or_insert_with(|| 3);
+    /// assert_eq!(map["poneyland"], 3);
+    ///
+    /// // existing key
+    /// *map.entry_ref("poneyland").or_insert_with(|| 10) *= 2;
+    /// assert_eq!(map["poneyland"], 6);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V
+    where
+        K: Hash + From<&'b Q>,
+        S: BuildHasher,
+    {
+        match self {
+            EntryRef::Occupied(entry) => entry.into_mut(),
+            EntryRef::Vacant(entry) => entry.insert(default()),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting, if empty, the result of the default function.
+    /// This method allows for generating key-derived values for insertion by providing the default
+    /// function a reference to the key that was moved during the `.entry_ref(key)` method call.
+    ///
+    /// The reference to the moved key is provided so that cloning or copying the key is
+    /// unnecessary, unlike with `.or_insert_with(|| ... )`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, usize> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry_ref("poneyland").or_insert_with_key(|key| key.chars().count());
+    /// assert_eq!(map["poneyland"], 9);
+    ///
+    /// // existing key
+    /// *map.entry_ref("poneyland").or_insert_with_key(|key| key.chars().count() * 10) *= 2;
+    /// assert_eq!(map["poneyland"], 18);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert_with_key<F: FnOnce(&Q) -> V>(self, default: F) -> &'a mut V
+    where
+        K: Hash + Borrow<Q> + From<&'b Q>,
+        S: BuildHasher,
+    {
+        match self {
+            EntryRef::Occupied(entry) => entry.into_mut(),
+            EntryRef::Vacant(entry) => {
+                let value = default(entry.key.as_ref());
+                entry.insert(value)
+            }
+        }
+    }
+
+    /// Returns a reference to this entry's key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// map.entry_ref("poneyland").or_insert(3);
+    /// // existing key
+    /// assert_eq!(map.entry_ref("poneyland").key(), "poneyland");
+    /// // nonexistent key
+    /// assert_eq!(map.entry_ref("horseland").key(), "horseland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key(&self) -> &Q
+    where
+        K: Borrow<Q>,
+    {
+        match *self {
+            EntryRef::Occupied(ref entry) => entry.key(),
+            EntryRef::Vacant(ref entry) => entry.key(),
+        }
+    }
+
+    /// Provides in-place mutable access to an occupied entry before any
+    /// potential inserts into the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    ///
+    /// map.entry_ref("poneyland")
+    ///    .and_modify(|e| { *e += 1 })
+    ///    .or_insert(42);
+    /// assert_eq!(map["poneyland"], 42);
+    ///
+    /// map.entry_ref("poneyland")
+    ///    .and_modify(|e| { *e += 1 })
+    ///    .or_insert(42);
+    /// assert_eq!(map["poneyland"], 43);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn and_modify<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&mut V),
+    {
+        match self {
+            EntryRef::Occupied(mut entry) => {
+                f(entry.get_mut());
+                EntryRef::Occupied(entry)
+            }
+            EntryRef::Vacant(entry) => EntryRef::Vacant(entry),
+        }
+    }
+
+    /// Provides shared access to the key and owned access to the value of
+    /// an occupied entry and allows to replace or remove it based on the
+    /// value of the returned option.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    ///
+    /// let entry = map
+    ///     .entry_ref("poneyland")
+    ///     .and_replace_entry_with(|_k, _v| panic!());
+    ///
+    /// match entry {
+    ///     EntryRef::Vacant(e) => {
+    ///         assert_eq!(e.key(), "poneyland");
+    ///     }
+    ///     EntryRef::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// map.insert("poneyland".to_string(), 42);
+    ///
+    /// let entry = map
+    ///     .entry_ref("poneyland")
+    ///     .and_replace_entry_with(|k, v| {
+    ///         assert_eq!(k, "poneyland");
+    ///         assert_eq!(v, 42);
+    ///         Some(v + 1)
+    ///     });
+    ///
+    /// match entry {
+    ///     EntryRef::Occupied(e) => {
+    ///         assert_eq!(e.key(), "poneyland");
+    ///         assert_eq!(e.get(), &43);
+    ///     }
+    ///     EntryRef::Vacant(_) => panic!(),
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 43);
+    ///
+    /// let entry = map
+    ///     .entry_ref("poneyland")
+    ///     .and_replace_entry_with(|_k, _v| None);
+    ///
+    /// match entry {
+    ///     EntryRef::Vacant(e) => assert_eq!(e.key(), "poneyland"),
+    ///     EntryRef::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// assert!(!map.contains_key("poneyland"));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn and_replace_entry_with<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&Q, V) -> Option<V>,
+        K: Borrow<Q>,
+    {
+        match self {
+            EntryRef::Occupied(entry) => entry.replace_entry_with(f),
+            EntryRef::Vacant(_) => self,
+        }
+    }
+}
+
+impl<'a, 'b, K, Q: ?Sized, V: Default, S, A: Allocator + Clone> EntryRef<'a, 'b, K, Q, V, S, A> {
+    /// Ensures a value is in the entry by inserting the default value if empty,
+    /// and returns a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, Option<u32>> = HashMap::new();
+    ///
+    /// // nonexistent key
+    /// map.entry_ref("poneyland").or_default();
+    /// assert_eq!(map["poneyland"], None);
+    ///
+    /// map.insert("horseland".to_string(), Some(3));
+    ///
+    /// // existing key
+    /// assert_eq!(map.entry_ref("horseland").or_default(), &mut Some(3));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_default(self) -> &'a mut V
+    where
+        K: Hash + From<&'b Q>,
+        S: BuildHasher,
+    {
+        match self {
+            EntryRef::Occupied(entry) => entry.into_mut(),
+            EntryRef::Vacant(entry) => entry.insert(Default::default()),
+        }
+    }
+}
+
+impl<'a, 'b, K, Q: ?Sized, V, S, A: Allocator + Clone> OccupiedEntryRef<'a, 'b, K, Q, V, S, A> {
+    /// Gets a reference to the key in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{EntryRef, HashMap};
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// map.entry_ref("poneyland").or_insert(12);
+    ///
+    /// match map.entry_ref("poneyland") {
+    ///     EntryRef::Vacant(_) => panic!(),
+    ///     EntryRef::Occupied(entry) => assert_eq!(entry.key(), "poneyland"),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key(&self) -> &Q
+    where
+        K: Borrow<Q>,
+    {
+        unsafe { &self.elem.as_ref().0 }.borrow()
+    }
+
+    /// Take the ownership of the key and value from the map.
+    /// Keeps the allocated memory for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// // The map is empty
+    /// assert!(map.is_empty() && map.capacity() == 0);
+    ///
+    /// map.entry_ref("poneyland").or_insert(12);
+    /// let capacity_before_remove = map.capacity();
+    ///
+    /// if let EntryRef::Occupied(o) = map.entry_ref("poneyland") {
+    ///     // We delete the entry from the map.
+    ///     assert_eq!(o.remove_entry(), ("poneyland".to_owned(), 12));
+    /// }
+    ///
+    /// assert_eq!(map.contains_key("poneyland"), false);
+    /// // Now map hold none elements but capacity is equal to the old one
+    /// assert!(map.len() == 0 && map.capacity() == capacity_before_remove);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove_entry(self) -> (K, V) {
+        unsafe { self.table.table.remove(self.elem) }
+    }
+
+    /// Gets a reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// map.entry_ref("poneyland").or_insert(12);
+    ///
+    /// match map.entry_ref("poneyland") {
+    ///     EntryRef::Vacant(_) => panic!(),
+    ///     EntryRef::Occupied(entry) => assert_eq!(entry.get(), &12),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get(&self) -> &V {
+        unsafe { &self.elem.as_ref().1 }
+    }
+
+    /// Gets a mutable reference to the value in the entry.
+    ///
+    /// If you need a reference to the `OccupiedEntryRef` which may outlive the
+    /// destruction of the `EntryRef` value, see [`into_mut`].
+    ///
+    /// [`into_mut`]: #method.into_mut
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// map.entry_ref("poneyland").or_insert(12);
+    ///
+    /// assert_eq!(map["poneyland"], 12);
+    /// if let EntryRef::Occupied(mut o) = map.entry_ref("poneyland") {
+    ///     *o.get_mut() += 10;
+    ///     assert_eq!(*o.get(), 22);
+    ///
+    ///     // We can use the same Entry multiple times.
+    ///     *o.get_mut() += 2;
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 24);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_mut(&mut self) -> &mut V {
+        unsafe { &mut self.elem.as_mut().1 }
+    }
+
+    /// Converts the OccupiedEntryRef into a mutable reference to the value in the entry
+    /// with a lifetime bound to the map itself.
+    ///
+    /// If you need multiple references to the `OccupiedEntryRef`, see [`get_mut`].
+    ///
+    /// [`get_mut`]: #method.get_mut
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{EntryRef, HashMap};
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// map.entry_ref("poneyland").or_insert(12);
+    ///
+    /// let value: &mut u32;
+    /// match map.entry_ref("poneyland") {
+    ///     EntryRef::Occupied(entry) => value = entry.into_mut(),
+    ///     EntryRef::Vacant(_) => panic!(),
+    /// }
+    /// *value += 10;
+    ///
+    /// assert_eq!(map["poneyland"], 22);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_mut(self) -> &'a mut V {
+        unsafe { &mut self.elem.as_mut().1 }
+    }
+
+    /// Sets the value of the entry, and returns the entry's old value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// map.entry_ref("poneyland").or_insert(12);
+    ///
+    /// if let EntryRef::Occupied(mut o) = map.entry_ref("poneyland") {
+    ///     assert_eq!(o.insert(15), 12);
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 15);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(&mut self, value: V) -> V {
+        mem::replace(self.get_mut(), value)
+    }
+
+    /// Takes the value out of the entry, and returns it.
+    /// Keeps the allocated memory for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// // The map is empty
+    /// assert!(map.is_empty() && map.capacity() == 0);
+    ///
+    /// map.entry_ref("poneyland").or_insert(12);
+    /// let capacity_before_remove = map.capacity();
+    ///
+    /// if let EntryRef::Occupied(o) = map.entry_ref("poneyland") {
+    ///     assert_eq!(o.remove(), 12);
+    /// }
+    ///
+    /// assert_eq!(map.contains_key("poneyland"), false);
+    /// // Now map hold none elements but capacity is equal to the old one
+    /// assert!(map.len() == 0 && map.capacity() == capacity_before_remove);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove(self) -> V {
+        self.remove_entry().1
+    }
+
+    /// Replaces the entry, returning the old key and value. The new key in the hash map will be
+    /// the key used to create this entry.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if this OccupiedEntry was created through [`EntryRef::insert`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{EntryRef, HashMap};
+    /// use std::rc::Rc;
+    ///
+    /// let mut map: HashMap<Rc<str>, u32> = HashMap::new();
+    /// let key: Rc<str> = Rc::from("Stringthing");
+    ///
+    /// map.insert(key.clone(), 15);
+    /// assert_eq!(Rc::strong_count(&key), 2);
+    ///
+    /// match map.entry_ref("Stringthing") {
+    ///     EntryRef::Occupied(entry) => {
+    ///         let (old_key, old_value): (Rc<str>, u32) = entry.replace_entry(16);
+    ///         assert!(Rc::ptr_eq(&key, &old_key) && old_value == 15);
+    ///     }
+    ///     EntryRef::Vacant(_) => panic!(),
+    /// }
+    ///
+    /// assert_eq!(Rc::strong_count(&key), 1);
+    /// assert_eq!(map["Stringthing"], 16);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace_entry(self, value: V) -> (K, V)
+    where
+        K: From<&'b Q>,
+    {
+        let entry = unsafe { self.elem.as_mut() };
+
+        let old_key = mem::replace(&mut entry.0, self.key.unwrap().into_owned());
+        let old_value = mem::replace(&mut entry.1, value);
+
+        (old_key, old_value)
+    }
+
+    /// Replaces the key in the hash map with the key used to create this entry.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if this OccupiedEntry was created through [`Entry::insert`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{EntryRef, HashMap};
+    /// use std::rc::Rc;
+    ///
+    /// let mut map: HashMap<Rc<str>, usize> = HashMap::with_capacity(6);
+    /// let mut keys: Vec<Rc<str>> = Vec::with_capacity(6);
+    ///
+    /// for (value, key) in ["a", "b", "c", "d", "e", "f"].into_iter().enumerate() {
+    ///     let rc_key: Rc<str> = Rc::from(key);
+    ///     keys.push(rc_key.clone());
+    ///     map.insert(rc_key.clone(), value);
+    /// }
+    ///
+    /// assert!(keys.iter().all(|key| Rc::strong_count(key) == 2));
+    ///
+    /// // It doesn't matter that we kind of use a vector with the same keys,
+    /// // because all keys will be newly created from the references
+    /// reclaim_memory(&mut map, &keys);
+    ///
+    /// assert!(keys.iter().all(|key| Rc::strong_count(key) == 1));
+    ///
+    /// fn reclaim_memory(map: &mut HashMap<Rc<str>, usize>, keys: &[Rc<str>]) {
+    ///     for key in keys {
+    ///         if let EntryRef::Occupied(entry) = map.entry_ref(key.as_ref()) {
+    ///         /// Replaces the entry's key with our version of it in `keys`.
+    ///             entry.replace_key();
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace_key(self) -> K
+    where
+        K: From<&'b Q>,
+    {
+        let entry = unsafe { self.elem.as_mut() };
+        mem::replace(&mut entry.0, self.key.unwrap().into_owned())
+    }
+
+    /// Provides shared access to the key and owned access to the value of
+    /// the entry and allows to replace or remove it based on the
+    /// value of the returned option.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// map.insert("poneyland".to_string(), 42);
+    ///
+    /// let entry = match map.entry_ref("poneyland") {
+    ///     EntryRef::Occupied(e) => {
+    ///         e.replace_entry_with(|k, v| {
+    ///             assert_eq!(k, "poneyland");
+    ///             assert_eq!(v, 42);
+    ///             Some(v + 1)
+    ///         })
+    ///     }
+    ///     EntryRef::Vacant(_) => panic!(),
+    /// };
+    ///
+    /// match entry {
+    ///     EntryRef::Occupied(e) => {
+    ///         assert_eq!(e.key(), "poneyland");
+    ///         assert_eq!(e.get(), &43);
+    ///     }
+    ///     EntryRef::Vacant(_) => panic!(),
+    /// }
+    ///
+    /// assert_eq!(map["poneyland"], 43);
+    ///
+    /// let entry = match map.entry_ref("poneyland") {
+    ///     EntryRef::Occupied(e) => e.replace_entry_with(|_k, _v| None),
+    ///     EntryRef::Vacant(_) => panic!(),
+    /// };
+    ///
+    /// match entry {
+    ///     EntryRef::Vacant(e) => {
+    ///         assert_eq!(e.key(), "poneyland");
+    ///     }
+    ///     EntryRef::Occupied(_) => panic!(),
+    /// }
+    ///
+    /// assert!(!map.contains_key("poneyland"));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace_entry_with<F>(self, f: F) -> EntryRef<'a, 'b, K, Q, V, S, A>
+    where
+        F: FnOnce(&Q, V) -> Option<V>,
+        K: Borrow<Q>,
+    {
+        unsafe {
+            let mut spare_key = None;
+
+            self.table
+                .table
+                .replace_bucket_with(self.elem.clone(), |(key, value)| {
+                    if let Some(new_value) = f(key.borrow(), value) {
+                        Some((key, new_value))
+                    } else {
+                        spare_key = Some(KeyOrRef::Owned(key));
+                        None
+                    }
+                });
+
+            if let Some(key) = spare_key {
+                EntryRef::Vacant(VacantEntryRef {
+                    hash: self.hash,
+                    key,
+                    table: self.table,
+                })
+            } else {
+                EntryRef::Occupied(self)
+            }
+        }
+    }
+}
+
+impl<'a, 'b, K, Q: ?Sized, V, S, A: Allocator + Clone> VacantEntryRef<'a, 'b, K, Q, V, S, A> {
+    /// Gets a reference to the key that would be used when inserting a value
+    /// through the `VacantEntryRef`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// let key: &str = "poneyland";
+    /// assert_eq!(map.entry_ref(key).key(), "poneyland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn key(&self) -> &Q
+    where
+        K: Borrow<Q>,
+    {
+        self.key.as_ref()
+    }
+
+    /// Take ownership of the key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::{EntryRef, HashMap};
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// let key: &str = "poneyland";
+    ///
+    /// match map.entry_ref(key) {
+    ///     EntryRef::Occupied(_) => panic!(),
+    ///     EntryRef::Vacant(v) => assert_eq!(v.into_key(), "poneyland".to_owned()),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_key(self) -> K
+    where
+        K: From<&'b Q>,
+    {
+        self.key.into_owned()
+    }
+
+    /// Sets the value of the entry with the VacantEntryRef's key,
+    /// and returns a mutable reference to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashMap;
+    /// use hashbrown::hash_map::EntryRef;
+    ///
+    /// let mut map: HashMap<String, u32> = HashMap::new();
+    /// let key: &str = "poneyland";
+    ///
+    /// if let EntryRef::Vacant(o) = map.entry_ref(key) {
+    ///     o.insert(37);
+    /// }
+    /// assert_eq!(map["poneyland"], 37);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self, value: V) -> &'a mut V
+    where
+        K: Hash + From<&'b Q>,
+        S: BuildHasher,
+    {
+        let table = &mut self.table.table;
+        let entry = table.insert_entry(
+            self.hash,
+            (self.key.into_owned(), value),
+            make_hasher::<K, _, V, S>(&self.table.hash_builder),
+        );
+        &mut entry.1
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn insert_entry(self, value: V) -> OccupiedEntryRef<'a, 'b, K, Q, V, S, A>
+    where
+        K: Hash + From<&'b Q>,
+        S: BuildHasher,
+    {
+        let elem = self.table.table.insert(
+            self.hash,
+            (self.key.into_owned(), value),
+            make_hasher::<K, _, V, S>(&self.table.hash_builder),
+        );
+        OccupiedEntryRef {
+            hash: self.hash,
+            key: None,
+            elem,
+            table: self.table,
+        }
+    }
+}
+
+impl<K, V, S, A> FromIterator<(K, V)> for HashMap<K, V, S, A>
+where
+    K: Eq + Hash,
+    S: BuildHasher + Default,
+    A: Default + Allocator + Clone,
+{
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> Self {
+        let iter = iter.into_iter();
+        let mut map =
+            Self::with_capacity_and_hasher_in(iter.size_hint().0, S::default(), A::default());
+        iter.for_each(|(k, v)| {
+            map.insert(k, v);
+        });
+        map
+    }
+}
+
+/// Inserts all new key-values from the iterator and replaces values with existing
+/// keys with new values returned from the iterator.
+impl<K, V, S, A> Extend<(K, V)> for HashMap<K, V, S, A>
+where
+    K: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    /// Inserts all new key-values from the iterator to existing `HashMap<K, V, S, A>`.
+    /// Replace values with existing keys with new values returned from the iterator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, 100);
+    ///
+    /// let some_iter = [(1, 1), (2, 2)].into_iter();
+    /// map.extend(some_iter);
+    /// // Replace values with existing keys with new values returned from the iterator.
+    /// // So that the map.get(&1) doesn't return Some(&100).
+    /// assert_eq!(map.get(&1), Some(&1));
+    ///
+    /// let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
+    /// map.extend(some_vec);
+    ///
+    /// let some_arr = [(5, 5), (6, 6)];
+    /// map.extend(some_arr);
+    /// let old_map_len = map.len();
+    ///
+    /// // You can also extend from another HashMap
+    /// let mut new_map = HashMap::new();
+    /// new_map.extend(map);
+    /// assert_eq!(new_map.len(), old_map_len);
+    ///
+    /// let mut vec: Vec<_> = new_map.into_iter().collect();
+    /// // The `IntoIter` iterator produces items in arbitrary order, so the
+    /// // items must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
+        // Keys may be already present or show multiple times in the iterator.
+        // Reserve the entire hint lower bound if the map is empty.
+        // Otherwise reserve half the hint (rounded up), so the map
+        // will only resize twice in the worst case.
+        let iter = iter.into_iter();
+        let reserve = if self.is_empty() {
+            iter.size_hint().0
+        } else {
+            (iter.size_hint().0 + 1) / 2
+        };
+        self.reserve(reserve);
+        iter.for_each(move |(k, v)| {
+            self.insert(k, v);
+        });
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_one(&mut self, (k, v): (K, V)) {
+        self.insert(k, v);
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_reserve(&mut self, additional: usize) {
+        // Keys may be already present or show multiple times in the iterator.
+        // Reserve the entire hint lower bound if the map is empty.
+        // Otherwise reserve half the hint (rounded up), so the map
+        // will only resize twice in the worst case.
+        let reserve = if self.is_empty() {
+            additional
+        } else {
+            (additional + 1) / 2
+        };
+        self.reserve(reserve);
+    }
+}
+
+/// Inserts all new key-values from the iterator and replaces values with existing
+/// keys with new values returned from the iterator.
+impl<'a, K, V, S, A> Extend<(&'a K, &'a V)> for HashMap<K, V, S, A>
+where
+    K: Eq + Hash + Copy,
+    V: Copy,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    /// Inserts all new key-values from the iterator to existing `HashMap<K, V, S, A>`.
+    /// Replace values with existing keys with new values returned from the iterator.
+    /// The keys and values must implement [`Copy`] trait.
+    ///
+    /// [`Copy`]: https://doc.rust-lang.org/core/marker/trait.Copy.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, 100);
+    ///
+    /// let arr = [(1, 1), (2, 2)];
+    /// let some_iter = arr.iter().map(|&(k, v)| (k, v));
+    /// map.extend(some_iter);
+    /// // Replace values with existing keys with new values returned from the iterator.
+    /// // So that the map.get(&1) doesn't return Some(&100).
+    /// assert_eq!(map.get(&1), Some(&1));
+    ///
+    /// let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
+    /// map.extend(some_vec.iter().map(|&(k, v)| (k, v)));
+    ///
+    /// let some_arr = [(5, 5), (6, 6)];
+    /// map.extend(some_arr.iter().map(|&(k, v)| (k, v)));
+    ///
+    /// // You can also extend from another HashMap
+    /// let mut new_map = HashMap::new();
+    /// new_map.extend(&map);
+    /// assert_eq!(new_map, map);
+    ///
+    /// let mut vec: Vec<_> = new_map.into_iter().collect();
+    /// // The `IntoIter` iterator produces items in arbitrary order, so the
+    /// // items must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
+        self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_one(&mut self, (k, v): (&'a K, &'a V)) {
+        self.insert(*k, *v);
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_reserve(&mut self, additional: usize) {
+        Extend::<(K, V)>::extend_reserve(self, additional);
+    }
+}
+
+/// Inserts all new key-values from the iterator and replaces values with existing
+/// keys with new values returned from the iterator.
+impl<'a, K, V, S, A> Extend<&'a (K, V)> for HashMap<K, V, S, A>
+where
+    K: Eq + Hash + Copy,
+    V: Copy,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    /// Inserts all new key-values from the iterator to existing `HashMap<K, V, S, A>`.
+    /// Replace values with existing keys with new values returned from the iterator.
+    /// The keys and values must implement [`Copy`] trait.
+    ///
+    /// [`Copy`]: https://doc.rust-lang.org/core/marker/trait.Copy.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_map::HashMap;
+    ///
+    /// let mut map = HashMap::new();
+    /// map.insert(1, 100);
+    ///
+    /// let arr = [(1, 1), (2, 2)];
+    /// let some_iter = arr.iter();
+    /// map.extend(some_iter);
+    /// // Replace values with existing keys with new values returned from the iterator.
+    /// // So that the map.get(&1) doesn't return Some(&100).
+    /// assert_eq!(map.get(&1), Some(&1));
+    ///
+    /// let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
+    /// map.extend(&some_vec);
+    ///
+    /// let some_arr = [(5, 5), (6, 6)];
+    /// map.extend(&some_arr);
+    ///
+    /// let mut vec: Vec<_> = map.into_iter().collect();
+    /// // The `IntoIter` iterator produces items in arbitrary order, so the
+    /// // items must be sorted to test them against a sorted array.
+    /// vec.sort_unstable();
+    /// assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn extend<T: IntoIterator<Item = &'a (K, V)>>(&mut self, iter: T) {
+        self.extend(iter.into_iter().map(|&(key, value)| (key, value)));
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_one(&mut self, &(k, v): &'a (K, V)) {
+        self.insert(k, v);
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_reserve(&mut self, additional: usize) {
+        Extend::<(K, V)>::extend_reserve(self, additional);
+    }
+}
+
+#[allow(dead_code)]
+fn assert_covariance() {
+    fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
+        v
+    }
+    fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
+        v
+    }
+    fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
+        v
+    }
+    fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
+        v
+    }
+    fn into_iter_key<'new, A: Allocator + Clone>(
+        v: IntoIter<&'static str, u8, A>,
+    ) -> IntoIter<&'new str, u8, A> {
+        v
+    }
+    fn into_iter_val<'new, A: Allocator + Clone>(
+        v: IntoIter<u8, &'static str, A>,
+    ) -> IntoIter<u8, &'new str, A> {
+        v
+    }
+    fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
+        v
+    }
+    fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
+        v
+    }
+    fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
+        v
+    }
+    fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
+        v
+    }
+    fn drain<'new>(
+        d: Drain<'static, &'static str, &'static str>,
+    ) -> Drain<'new, &'new str, &'new str> {
+        d
+    }
+}
+
+#[cfg(test)]
+mod test_map {
+    use super::DefaultHashBuilder;
+    use super::Entry::{Occupied, Vacant};
+    use super::EntryRef;
+    use super::{HashMap, RawEntryMut};
+    use rand::{rngs::SmallRng, Rng, SeedableRng};
+    use std::borrow::ToOwned;
+    use std::cell::RefCell;
+    use std::usize;
+    use std::vec::Vec;
+
+    #[test]
+    fn test_zero_capacities() {
+        type HM = HashMap<i32, i32>;
+
+        let m = HM::new();
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::default();
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::with_hasher(DefaultHashBuilder::default());
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::with_capacity(0);
+        assert_eq!(m.capacity(), 0);
+
+        let m = HM::with_capacity_and_hasher(0, DefaultHashBuilder::default());
+        assert_eq!(m.capacity(), 0);
+
+        let mut m = HM::new();
+        m.insert(1, 1);
+        m.insert(2, 2);
+        m.remove(&1);
+        m.remove(&2);
+        m.shrink_to_fit();
+        assert_eq!(m.capacity(), 0);
+
+        let mut m = HM::new();
+        m.reserve(0);
+        assert_eq!(m.capacity(), 0);
+    }
+
+    #[test]
+    fn test_create_capacity_zero() {
+        let mut m = HashMap::with_capacity(0);
+
+        assert!(m.insert(1, 1).is_none());
+
+        assert!(m.contains_key(&1));
+        assert!(!m.contains_key(&0));
+    }
+
+    #[test]
+    fn test_insert() {
+        let mut m = HashMap::new();
+        assert_eq!(m.len(), 0);
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(m.len(), 1);
+        assert!(m.insert(2, 4).is_none());
+        assert_eq!(m.len(), 2);
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert_eq!(*m.get(&2).unwrap(), 4);
+    }
+
+    #[test]
+    fn test_clone() {
+        let mut m = HashMap::new();
+        assert_eq!(m.len(), 0);
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(m.len(), 1);
+        assert!(m.insert(2, 4).is_none());
+        assert_eq!(m.len(), 2);
+        #[allow(clippy::redundant_clone)]
+        let m2 = m.clone();
+        assert_eq!(*m2.get(&1).unwrap(), 2);
+        assert_eq!(*m2.get(&2).unwrap(), 4);
+        assert_eq!(m2.len(), 2);
+    }
+
+    #[test]
+    fn test_clone_from() {
+        let mut m = HashMap::new();
+        let mut m2 = HashMap::new();
+        assert_eq!(m.len(), 0);
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(m.len(), 1);
+        assert!(m.insert(2, 4).is_none());
+        assert_eq!(m.len(), 2);
+        m2.clone_from(&m);
+        assert_eq!(*m2.get(&1).unwrap(), 2);
+        assert_eq!(*m2.get(&2).unwrap(), 4);
+        assert_eq!(m2.len(), 2);
+    }
+
+    thread_local! { static DROP_VECTOR: RefCell<Vec<i32>> = RefCell::new(Vec::new()) }
+
+    #[derive(Hash, PartialEq, Eq)]
+    struct Droppable {
+        k: usize,
+    }
+
+    impl Droppable {
+        fn new(k: usize) -> Droppable {
+            DROP_VECTOR.with(|slot| {
+                slot.borrow_mut()[k] += 1;
+            });
+
+            Droppable { k }
+        }
+    }
+
+    impl Drop for Droppable {
+        fn drop(&mut self) {
+            DROP_VECTOR.with(|slot| {
+                slot.borrow_mut()[self.k] -= 1;
+            });
+        }
+    }
+
+    impl Clone for Droppable {
+        fn clone(&self) -> Self {
+            Droppable::new(self.k)
+        }
+    }
+
+    #[test]
+    fn test_drops() {
+        DROP_VECTOR.with(|slot| {
+            *slot.borrow_mut() = vec![0; 200];
+        });
+
+        {
+            let mut m = HashMap::new();
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 0);
+                }
+            });
+
+            for i in 0..100 {
+                let d1 = Droppable::new(i);
+                let d2 = Droppable::new(i + 100);
+                m.insert(d1, d2);
+            }
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 1);
+                }
+            });
+
+            for i in 0..50 {
+                let k = Droppable::new(i);
+                let v = m.remove(&k);
+
+                assert!(v.is_some());
+
+                DROP_VECTOR.with(|v| {
+                    assert_eq!(v.borrow()[i], 1);
+                    assert_eq!(v.borrow()[i + 100], 1);
+                });
+            }
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..50 {
+                    assert_eq!(v.borrow()[i], 0);
+                    assert_eq!(v.borrow()[i + 100], 0);
+                }
+
+                for i in 50..100 {
+                    assert_eq!(v.borrow()[i], 1);
+                    assert_eq!(v.borrow()[i + 100], 1);
+                }
+            });
+        }
+
+        DROP_VECTOR.with(|v| {
+            for i in 0..200 {
+                assert_eq!(v.borrow()[i], 0);
+            }
+        });
+    }
+
+    #[test]
+    fn test_into_iter_drops() {
+        DROP_VECTOR.with(|v| {
+            *v.borrow_mut() = vec![0; 200];
+        });
+
+        let hm = {
+            let mut hm = HashMap::new();
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 0);
+                }
+            });
+
+            for i in 0..100 {
+                let d1 = Droppable::new(i);
+                let d2 = Droppable::new(i + 100);
+                hm.insert(d1, d2);
+            }
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 1);
+                }
+            });
+
+            hm
+        };
+
+        // By the way, ensure that cloning doesn't screw up the dropping.
+        drop(hm.clone());
+
+        {
+            let mut half = hm.into_iter().take(50);
+
+            DROP_VECTOR.with(|v| {
+                for i in 0..200 {
+                    assert_eq!(v.borrow()[i], 1);
+                }
+            });
+
+            #[allow(clippy::let_underscore_drop)] // kind-of a false positive
+            for _ in half.by_ref() {}
+
+            DROP_VECTOR.with(|v| {
+                let nk = (0..100).filter(|&i| v.borrow()[i] == 1).count();
+
+                let nv = (0..100).filter(|&i| v.borrow()[i + 100] == 1).count();
+
+                assert_eq!(nk, 50);
+                assert_eq!(nv, 50);
+            });
+        };
+
+        DROP_VECTOR.with(|v| {
+            for i in 0..200 {
+                assert_eq!(v.borrow()[i], 0);
+            }
+        });
+    }
+
+    #[test]
+    fn test_empty_remove() {
+        let mut m: HashMap<i32, bool> = HashMap::new();
+        assert_eq!(m.remove(&0), None);
+    }
+
+    #[test]
+    fn test_empty_entry() {
+        let mut m: HashMap<i32, bool> = HashMap::new();
+        match m.entry(0) {
+            Occupied(_) => panic!(),
+            Vacant(_) => {}
+        }
+        assert!(*m.entry(0).or_insert(true));
+        assert_eq!(m.len(), 1);
+    }
+
+    #[test]
+    fn test_empty_entry_ref() {
+        let mut m: HashMap<std::string::String, bool> = HashMap::new();
+        match m.entry_ref("poneyland") {
+            EntryRef::Occupied(_) => panic!(),
+            EntryRef::Vacant(_) => {}
+        }
+        assert!(*m.entry_ref("poneyland").or_insert(true));
+        assert_eq!(m.len(), 1);
+    }
+
+    #[test]
+    fn test_empty_iter() {
+        let mut m: HashMap<i32, bool> = HashMap::new();
+        assert_eq!(m.drain().next(), None);
+        assert_eq!(m.keys().next(), None);
+        assert_eq!(m.values().next(), None);
+        assert_eq!(m.values_mut().next(), None);
+        assert_eq!(m.iter().next(), None);
+        assert_eq!(m.iter_mut().next(), None);
+        assert_eq!(m.len(), 0);
+        assert!(m.is_empty());
+        assert_eq!(m.into_iter().next(), None);
+    }
+
+    #[test]
+    #[cfg_attr(miri, ignore)] // FIXME: takes too long
+    fn test_lots_of_insertions() {
+        let mut m = HashMap::new();
+
+        // Try this a few times to make sure we never screw up the hashmap's
+        // internal state.
+        for _ in 0..10 {
+            assert!(m.is_empty());
+
+            for i in 1..1001 {
+                assert!(m.insert(i, i).is_none());
+
+                for j in 1..=i {
+                    let r = m.get(&j);
+                    assert_eq!(r, Some(&j));
+                }
+
+                for j in i + 1..1001 {
+                    let r = m.get(&j);
+                    assert_eq!(r, None);
+                }
+            }
+
+            for i in 1001..2001 {
+                assert!(!m.contains_key(&i));
+            }
+
+            // remove forwards
+            for i in 1..1001 {
+                assert!(m.remove(&i).is_some());
+
+                for j in 1..=i {
+                    assert!(!m.contains_key(&j));
+                }
+
+                for j in i + 1..1001 {
+                    assert!(m.contains_key(&j));
+                }
+            }
+
+            for i in 1..1001 {
+                assert!(!m.contains_key(&i));
+            }
+
+            for i in 1..1001 {
+                assert!(m.insert(i, i).is_none());
+            }
+
+            // remove backwards
+            for i in (1..1001).rev() {
+                assert!(m.remove(&i).is_some());
+
+                for j in i..1001 {
+                    assert!(!m.contains_key(&j));
+                }
+
+                for j in 1..i {
+                    assert!(m.contains_key(&j));
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_find_mut() {
+        let mut m = HashMap::new();
+        assert!(m.insert(1, 12).is_none());
+        assert!(m.insert(2, 8).is_none());
+        assert!(m.insert(5, 14).is_none());
+        let new = 100;
+        match m.get_mut(&5) {
+            None => panic!(),
+            Some(x) => *x = new,
+        }
+        assert_eq!(m.get(&5), Some(&new));
+    }
+
+    #[test]
+    fn test_insert_overwrite() {
+        let mut m = HashMap::new();
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert!(m.insert(1, 3).is_some());
+        assert_eq!(*m.get(&1).unwrap(), 3);
+    }
+
+    #[test]
+    fn test_insert_conflicts() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2).is_none());
+        assert!(m.insert(5, 3).is_none());
+        assert!(m.insert(9, 4).is_none());
+        assert_eq!(*m.get(&9).unwrap(), 4);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+        assert_eq!(*m.get(&1).unwrap(), 2);
+    }
+
+    #[test]
+    fn test_conflict_remove() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert!(m.insert(5, 3).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+        assert!(m.insert(9, 4).is_none());
+        assert_eq!(*m.get(&1).unwrap(), 2);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+        assert_eq!(*m.get(&9).unwrap(), 4);
+        assert!(m.remove(&1).is_some());
+        assert_eq!(*m.get(&9).unwrap(), 4);
+        assert_eq!(*m.get(&5).unwrap(), 3);
+    }
+
+    #[test]
+    fn test_insert_unique_unchecked() {
+        let mut map = HashMap::new();
+        let (k1, v1) = map.insert_unique_unchecked(10, 11);
+        assert_eq!((&10, &mut 11), (k1, v1));
+        let (k2, v2) = map.insert_unique_unchecked(20, 21);
+        assert_eq!((&20, &mut 21), (k2, v2));
+        assert_eq!(Some(&11), map.get(&10));
+        assert_eq!(Some(&21), map.get(&20));
+        assert_eq!(None, map.get(&30));
+    }
+
+    #[test]
+    fn test_is_empty() {
+        let mut m = HashMap::with_capacity(4);
+        assert!(m.insert(1, 2).is_none());
+        assert!(!m.is_empty());
+        assert!(m.remove(&1).is_some());
+        assert!(m.is_empty());
+    }
+
+    #[test]
+    fn test_remove() {
+        let mut m = HashMap::new();
+        m.insert(1, 2);
+        assert_eq!(m.remove(&1), Some(2));
+        assert_eq!(m.remove(&1), None);
+    }
+
+    #[test]
+    fn test_remove_entry() {
+        let mut m = HashMap::new();
+        m.insert(1, 2);
+        assert_eq!(m.remove_entry(&1), Some((1, 2)));
+        assert_eq!(m.remove(&1), None);
+    }
+
+    #[test]
+    fn test_iterate() {
+        let mut m = HashMap::with_capacity(4);
+        for i in 0..32 {
+            assert!(m.insert(i, i * 2).is_none());
+        }
+        assert_eq!(m.len(), 32);
+
+        let mut observed: u32 = 0;
+
+        for (k, v) in &m {
+            assert_eq!(*v, *k * 2);
+            observed |= 1 << *k;
+        }
+        assert_eq!(observed, 0xFFFF_FFFF);
+    }
+
+    #[test]
+    fn test_keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: HashMap<_, _> = vec.into_iter().collect();
+        let keys: Vec<_> = map.keys().copied().collect();
+        assert_eq!(keys.len(), 3);
+        assert!(keys.contains(&1));
+        assert!(keys.contains(&2));
+        assert!(keys.contains(&3));
+    }
+
+    #[test]
+    fn test_values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: HashMap<_, _> = vec.into_iter().collect();
+        let values: Vec<_> = map.values().copied().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&'a'));
+        assert!(values.contains(&'b'));
+        assert!(values.contains(&'c'));
+    }
+
+    #[test]
+    fn test_values_mut() {
+        let vec = vec![(1, 1), (2, 2), (3, 3)];
+        let mut map: HashMap<_, _> = vec.into_iter().collect();
+        for value in map.values_mut() {
+            *value *= 2;
+        }
+        let values: Vec<_> = map.values().copied().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&2));
+        assert!(values.contains(&4));
+        assert!(values.contains(&6));
+    }
+
+    #[test]
+    fn test_into_keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: HashMap<_, _> = vec.into_iter().collect();
+        let keys: Vec<_> = map.into_keys().collect();
+
+        assert_eq!(keys.len(), 3);
+        assert!(keys.contains(&1));
+        assert!(keys.contains(&2));
+        assert!(keys.contains(&3));
+    }
+
+    #[test]
+    fn test_into_values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: HashMap<_, _> = vec.into_iter().collect();
+        let values: Vec<_> = map.into_values().collect();
+
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&'a'));
+        assert!(values.contains(&'b'));
+        assert!(values.contains(&'c'));
+    }
+
+    #[test]
+    fn test_find() {
+        let mut m = HashMap::new();
+        assert!(m.get(&1).is_none());
+        m.insert(1, 2);
+        match m.get(&1) {
+            None => panic!(),
+            Some(v) => assert_eq!(*v, 2),
+        }
+    }
+
+    #[test]
+    fn test_eq() {
+        let mut m1 = HashMap::new();
+        m1.insert(1, 2);
+        m1.insert(2, 3);
+        m1.insert(3, 4);
+
+        let mut m2 = HashMap::new();
+        m2.insert(1, 2);
+        m2.insert(2, 3);
+
+        assert!(m1 != m2);
+
+        m2.insert(3, 4);
+
+        assert_eq!(m1, m2);
+    }
+
+    #[test]
+    fn test_show() {
+        let mut map = HashMap::new();
+        let empty: HashMap<i32, i32> = HashMap::new();
+
+        map.insert(1, 2);
+        map.insert(3, 4);
+
+        let map_str = format!("{:?}", map);
+
+        assert!(map_str == "{1: 2, 3: 4}" || map_str == "{3: 4, 1: 2}");
+        assert_eq!(format!("{:?}", empty), "{}");
+    }
+
+    #[test]
+    fn test_expand() {
+        let mut m = HashMap::new();
+
+        assert_eq!(m.len(), 0);
+        assert!(m.is_empty());
+
+        let mut i = 0;
+        let old_raw_cap = m.raw_capacity();
+        while old_raw_cap == m.raw_capacity() {
+            m.insert(i, i);
+            i += 1;
+        }
+
+        assert_eq!(m.len(), i);
+        assert!(!m.is_empty());
+    }
+
+    #[test]
+    fn test_behavior_resize_policy() {
+        let mut m = HashMap::new();
+
+        assert_eq!(m.len(), 0);
+        assert_eq!(m.raw_capacity(), 1);
+        assert!(m.is_empty());
+
+        m.insert(0, 0);
+        m.remove(&0);
+        assert!(m.is_empty());
+        let initial_raw_cap = m.raw_capacity();
+        m.reserve(initial_raw_cap);
+        let raw_cap = m.raw_capacity();
+
+        assert_eq!(raw_cap, initial_raw_cap * 2);
+
+        let mut i = 0;
+        for _ in 0..raw_cap * 3 / 4 {
+            m.insert(i, i);
+            i += 1;
+        }
+        // three quarters full
+
+        assert_eq!(m.len(), i);
+        assert_eq!(m.raw_capacity(), raw_cap);
+
+        for _ in 0..raw_cap / 4 {
+            m.insert(i, i);
+            i += 1;
+        }
+        // half full
+
+        let new_raw_cap = m.raw_capacity();
+        assert_eq!(new_raw_cap, raw_cap * 2);
+
+        for _ in 0..raw_cap / 2 - 1 {
+            i -= 1;
+            m.remove(&i);
+            assert_eq!(m.raw_capacity(), new_raw_cap);
+        }
+        // A little more than one quarter full.
+        m.shrink_to_fit();
+        assert_eq!(m.raw_capacity(), raw_cap);
+        // again, a little more than half full
+        for _ in 0..raw_cap / 2 {
+            i -= 1;
+            m.remove(&i);
+        }
+        m.shrink_to_fit();
+
+        assert_eq!(m.len(), i);
+        assert!(!m.is_empty());
+        assert_eq!(m.raw_capacity(), initial_raw_cap);
+    }
+
+    #[test]
+    fn test_reserve_shrink_to_fit() {
+        let mut m = HashMap::new();
+        m.insert(0, 0);
+        m.remove(&0);
+        assert!(m.capacity() >= m.len());
+        for i in 0..128 {
+            m.insert(i, i);
+        }
+        m.reserve(256);
+
+        let usable_cap = m.capacity();
+        for i in 128..(128 + 256) {
+            m.insert(i, i);
+            assert_eq!(m.capacity(), usable_cap);
+        }
+
+        for i in 100..(128 + 256) {
+            assert_eq!(m.remove(&i), Some(i));
+        }
+        m.shrink_to_fit();
+
+        assert_eq!(m.len(), 100);
+        assert!(!m.is_empty());
+        assert!(m.capacity() >= m.len());
+
+        for i in 0..100 {
+            assert_eq!(m.remove(&i), Some(i));
+        }
+        m.shrink_to_fit();
+        m.insert(0, 0);
+
+        assert_eq!(m.len(), 1);
+        assert!(m.capacity() >= m.len());
+        assert_eq!(m.remove(&0), Some(0));
+    }
+
+    #[test]
+    fn test_from_iter() {
+        let xs = [(1, 1), (2, 2), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<_, _> = xs.iter().copied().collect();
+
+        for &(k, v) in &xs {
+            assert_eq!(map.get(&k), Some(&v));
+        }
+
+        assert_eq!(map.iter().len(), xs.len() - 1);
+    }
+
+    #[test]
+    fn test_size_hint() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<_, _> = xs.iter().copied().collect();
+
+        let mut iter = map.iter();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.size_hint(), (3, Some(3)));
+    }
+
+    #[test]
+    fn test_iter_len() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let map: HashMap<_, _> = xs.iter().copied().collect();
+
+        let mut iter = map.iter();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.len(), 3);
+    }
+
+    #[test]
+    fn test_mut_size_hint() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let mut map: HashMap<_, _> = xs.iter().copied().collect();
+
+        let mut iter = map.iter_mut();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.size_hint(), (3, Some(3)));
+    }
+
+    #[test]
+    fn test_iter_mut_len() {
+        let xs = [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)];
+
+        let mut map: HashMap<_, _> = xs.iter().copied().collect();
+
+        let mut iter = map.iter_mut();
+
+        for _ in iter.by_ref().take(3) {}
+
+        assert_eq!(iter.len(), 3);
+    }
+
+    #[test]
+    fn test_index() {
+        let mut map = HashMap::new();
+
+        map.insert(1, 2);
+        map.insert(2, 1);
+        map.insert(3, 4);
+
+        assert_eq!(map[&2], 1);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_index_nonexistent() {
+        let mut map = HashMap::new();
+
+        map.insert(1, 2);
+        map.insert(2, 1);
+        map.insert(3, 4);
+
+        #[allow(clippy::no_effect)] // false positive lint
+        map[&4];
+    }
+
+    #[test]
+    fn test_entry() {
+        let xs = [(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)];
+
+        let mut map: HashMap<_, _> = xs.iter().copied().collect();
+
+        // Existing key (insert)
+        match map.entry(1) {
+            Vacant(_) => unreachable!(),
+            Occupied(mut view) => {
+                assert_eq!(view.get(), &10);
+                assert_eq!(view.insert(100), 10);
+            }
+        }
+        assert_eq!(map.get(&1).unwrap(), &100);
+        assert_eq!(map.len(), 6);
+
+        // Existing key (update)
+        match map.entry(2) {
+            Vacant(_) => unreachable!(),
+            Occupied(mut view) => {
+                let v = view.get_mut();
+                let new_v = (*v) * 10;
+                *v = new_v;
+            }
+        }
+        assert_eq!(map.get(&2).unwrap(), &200);
+        assert_eq!(map.len(), 6);
+
+        // Existing key (take)
+        match map.entry(3) {
+            Vacant(_) => unreachable!(),
+            Occupied(view) => {
+                assert_eq!(view.remove(), 30);
+            }
+        }
+        assert_eq!(map.get(&3), None);
+        assert_eq!(map.len(), 5);
+
+        // Inexistent key (insert)
+        match map.entry(10) {
+            Occupied(_) => unreachable!(),
+            Vacant(view) => {
+                assert_eq!(*view.insert(1000), 1000);
+            }
+        }
+        assert_eq!(map.get(&10).unwrap(), &1000);
+        assert_eq!(map.len(), 6);
+    }
+
+    #[test]
+    fn test_entry_ref() {
+        let xs = [
+            ("One".to_owned(), 10),
+            ("Two".to_owned(), 20),
+            ("Three".to_owned(), 30),
+            ("Four".to_owned(), 40),
+            ("Five".to_owned(), 50),
+            ("Six".to_owned(), 60),
+        ];
+
+        let mut map: HashMap<_, _> = xs.iter().cloned().collect();
+
+        // Existing key (insert)
+        match map.entry_ref("One") {
+            EntryRef::Vacant(_) => unreachable!(),
+            EntryRef::Occupied(mut view) => {
+                assert_eq!(view.get(), &10);
+                assert_eq!(view.insert(100), 10);
+            }
+        }
+        assert_eq!(map.get("One").unwrap(), &100);
+        assert_eq!(map.len(), 6);
+
+        // Existing key (update)
+        match map.entry_ref("Two") {
+            EntryRef::Vacant(_) => unreachable!(),
+            EntryRef::Occupied(mut view) => {
+                let v = view.get_mut();
+                let new_v = (*v) * 10;
+                *v = new_v;
+            }
+        }
+        assert_eq!(map.get("Two").unwrap(), &200);
+        assert_eq!(map.len(), 6);
+
+        // Existing key (take)
+        match map.entry_ref("Three") {
+            EntryRef::Vacant(_) => unreachable!(),
+            EntryRef::Occupied(view) => {
+                assert_eq!(view.remove(), 30);
+            }
+        }
+        assert_eq!(map.get("Three"), None);
+        assert_eq!(map.len(), 5);
+
+        // Inexistent key (insert)
+        match map.entry_ref("Ten") {
+            EntryRef::Occupied(_) => unreachable!(),
+            EntryRef::Vacant(view) => {
+                assert_eq!(*view.insert(1000), 1000);
+            }
+        }
+        assert_eq!(map.get("Ten").unwrap(), &1000);
+        assert_eq!(map.len(), 6);
+    }
+
+    #[test]
+    fn test_entry_take_doesnt_corrupt() {
+        #![allow(deprecated)] //rand
+                              // Test for #19292
+        fn check(m: &HashMap<i32, ()>) {
+            for k in m.keys() {
+                assert!(m.contains_key(k), "{} is in keys() but not in the map?", k);
+            }
+        }
+
+        let mut m = HashMap::new();
+
+        let mut rng = {
+            let seed = u64::from_le_bytes(*b"testseed");
+            SmallRng::seed_from_u64(seed)
+        };
+
+        // Populate the map with some items.
+        for _ in 0..50 {
+            let x = rng.gen_range(-10..10);
+            m.insert(x, ());
+        }
+
+        for _ in 0..1000 {
+            let x = rng.gen_range(-10..10);
+            match m.entry(x) {
+                Vacant(_) => {}
+                Occupied(e) => {
+                    e.remove();
+                }
+            }
+
+            check(&m);
+        }
+    }
+
+    #[test]
+    fn test_entry_ref_take_doesnt_corrupt() {
+        #![allow(deprecated)] //rand
+                              // Test for #19292
+        fn check(m: &HashMap<std::string::String, ()>) {
+            for k in m.keys() {
+                assert!(m.contains_key(k), "{} is in keys() but not in the map?", k);
+            }
+        }
+
+        let mut m = HashMap::new();
+
+        let mut rng = {
+            let seed = u64::from_le_bytes(*b"testseed");
+            SmallRng::seed_from_u64(seed)
+        };
+
+        // Populate the map with some items.
+        for _ in 0..50 {
+            let mut x = std::string::String::with_capacity(1);
+            x.push(rng.gen_range('a'..='z'));
+            m.insert(x, ());
+        }
+
+        for _ in 0..1000 {
+            let mut x = std::string::String::with_capacity(1);
+            x.push(rng.gen_range('a'..='z'));
+            match m.entry_ref(x.as_str()) {
+                EntryRef::Vacant(_) => {}
+                EntryRef::Occupied(e) => {
+                    e.remove();
+                }
+            }
+
+            check(&m);
+        }
+    }
+
+    #[test]
+    fn test_extend_ref_k_ref_v() {
+        let mut a = HashMap::new();
+        a.insert(1, "one");
+        let mut b = HashMap::new();
+        b.insert(2, "two");
+        b.insert(3, "three");
+
+        a.extend(&b);
+
+        assert_eq!(a.len(), 3);
+        assert_eq!(a[&1], "one");
+        assert_eq!(a[&2], "two");
+        assert_eq!(a[&3], "three");
+    }
+
+    #[test]
+    fn test_extend_ref_kv_tuple() {
+        use std::ops::AddAssign;
+        let mut a = HashMap::new();
+        a.insert(0, 0);
+
+        fn create_arr<T: AddAssign<T> + Copy, const N: usize>(start: T, step: T) -> [(T, T); N] {
+            let mut outs: [(T, T); N] = [(start, start); N];
+            let mut element = step;
+            outs.iter_mut().skip(1).for_each(|(k, v)| {
+                *k += element;
+                *v += element;
+                element += step;
+            });
+            outs
+        }
+
+        let for_iter: Vec<_> = (0..100).map(|i| (i, i)).collect();
+        let iter = for_iter.iter();
+        let vec: Vec<_> = (100..200).map(|i| (i, i)).collect();
+        a.extend(iter);
+        a.extend(&vec);
+        a.extend(&create_arr::<i32, 100>(200, 1));
+
+        assert_eq!(a.len(), 300);
+
+        for item in 0..300 {
+            assert_eq!(a[&item], item);
+        }
+    }
+
+    #[test]
+    fn test_capacity_not_less_than_len() {
+        let mut a = HashMap::new();
+        let mut item = 0;
+
+        for _ in 0..116 {
+            a.insert(item, 0);
+            item += 1;
+        }
+
+        assert!(a.capacity() > a.len());
+
+        let free = a.capacity() - a.len();
+        for _ in 0..free {
+            a.insert(item, 0);
+            item += 1;
+        }
+
+        assert_eq!(a.len(), a.capacity());
+
+        // Insert at capacity should cause allocation.
+        a.insert(item, 0);
+        assert!(a.capacity() > a.len());
+    }
+
+    #[test]
+    fn test_occupied_entry_key() {
+        let mut a = HashMap::new();
+        let key = "hello there";
+        let value = "value goes here";
+        assert!(a.is_empty());
+        a.insert(key, value);
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+
+        match a.entry(key) {
+            Vacant(_) => panic!(),
+            Occupied(e) => assert_eq!(key, *e.key()),
+        }
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+    }
+
+    #[test]
+    fn test_occupied_entry_ref_key() {
+        let mut a = HashMap::new();
+        let key = "hello there";
+        let value = "value goes here";
+        assert!(a.is_empty());
+        a.insert(key.to_owned(), value);
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+
+        match a.entry_ref(key) {
+            EntryRef::Vacant(_) => panic!(),
+            EntryRef::Occupied(e) => assert_eq!(key, e.key()),
+        }
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+    }
+
+    #[test]
+    fn test_vacant_entry_key() {
+        let mut a = HashMap::new();
+        let key = "hello there";
+        let value = "value goes here";
+
+        assert!(a.is_empty());
+        match a.entry(key) {
+            Occupied(_) => panic!(),
+            Vacant(e) => {
+                assert_eq!(key, *e.key());
+                e.insert(value);
+            }
+        }
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+    }
+
+    #[test]
+    fn test_vacant_entry_ref_key() {
+        let mut a: HashMap<std::string::String, &str> = HashMap::new();
+        let key = "hello there";
+        let value = "value goes here";
+
+        assert!(a.is_empty());
+        match a.entry_ref(key) {
+            EntryRef::Occupied(_) => panic!(),
+            EntryRef::Vacant(e) => {
+                assert_eq!(key, e.key());
+                e.insert(value);
+            }
+        }
+        assert_eq!(a.len(), 1);
+        assert_eq!(a[key], value);
+    }
+
+    #[test]
+    fn test_occupied_entry_replace_entry_with() {
+        let mut a = HashMap::new();
+
+        let key = "a key";
+        let value = "an initial value";
+        let new_value = "a new value";
+
+        let entry = a.entry(key).insert(value).replace_entry_with(|k, v| {
+            assert_eq!(k, &key);
+            assert_eq!(v, value);
+            Some(new_value)
+        });
+
+        match entry {
+            Occupied(e) => {
+                assert_eq!(e.key(), &key);
+                assert_eq!(e.get(), &new_value);
+            }
+            Vacant(_) => panic!(),
+        }
+
+        assert_eq!(a[key], new_value);
+        assert_eq!(a.len(), 1);
+
+        let entry = match a.entry(key) {
+            Occupied(e) => e.replace_entry_with(|k, v| {
+                assert_eq!(k, &key);
+                assert_eq!(v, new_value);
+                None
+            }),
+            Vacant(_) => panic!(),
+        };
+
+        match entry {
+            Vacant(e) => assert_eq!(e.key(), &key),
+            Occupied(_) => panic!(),
+        }
+
+        assert!(!a.contains_key(key));
+        assert_eq!(a.len(), 0);
+    }
+
+    #[test]
+    fn test_occupied_entry_ref_replace_entry_with() {
+        let mut a: HashMap<std::string::String, &str> = HashMap::new();
+
+        let key = "a key";
+        let value = "an initial value";
+        let new_value = "a new value";
+
+        let entry = a.entry_ref(key).insert(value).replace_entry_with(|k, v| {
+            assert_eq!(k, key);
+            assert_eq!(v, value);
+            Some(new_value)
+        });
+
+        match entry {
+            EntryRef::Occupied(e) => {
+                assert_eq!(e.key(), key);
+                assert_eq!(e.get(), &new_value);
+            }
+            EntryRef::Vacant(_) => panic!(),
+        }
+
+        assert_eq!(a[key], new_value);
+        assert_eq!(a.len(), 1);
+
+        let entry = match a.entry_ref(key) {
+            EntryRef::Occupied(e) => e.replace_entry_with(|k, v| {
+                assert_eq!(k, key);
+                assert_eq!(v, new_value);
+                None
+            }),
+            EntryRef::Vacant(_) => panic!(),
+        };
+
+        match entry {
+            EntryRef::Vacant(e) => assert_eq!(e.key(), key),
+            EntryRef::Occupied(_) => panic!(),
+        }
+
+        assert!(!a.contains_key(key));
+        assert_eq!(a.len(), 0);
+    }
+
+    #[test]
+    fn test_entry_and_replace_entry_with() {
+        let mut a = HashMap::new();
+
+        let key = "a key";
+        let value = "an initial value";
+        let new_value = "a new value";
+
+        let entry = a.entry(key).and_replace_entry_with(|_, _| panic!());
+
+        match entry {
+            Vacant(e) => assert_eq!(e.key(), &key),
+            Occupied(_) => panic!(),
+        }
+
+        a.insert(key, value);
+
+        let entry = a.entry(key).and_replace_entry_with(|k, v| {
+            assert_eq!(k, &key);
+            assert_eq!(v, value);
+            Some(new_value)
+        });
+
+        match entry {
+            Occupied(e) => {
+                assert_eq!(e.key(), &key);
+                assert_eq!(e.get(), &new_value);
+            }
+            Vacant(_) => panic!(),
+        }
+
+        assert_eq!(a[key], new_value);
+        assert_eq!(a.len(), 1);
+
+        let entry = a.entry(key).and_replace_entry_with(|k, v| {
+            assert_eq!(k, &key);
+            assert_eq!(v, new_value);
+            None
+        });
+
+        match entry {
+            Vacant(e) => assert_eq!(e.key(), &key),
+            Occupied(_) => panic!(),
+        }
+
+        assert!(!a.contains_key(key));
+        assert_eq!(a.len(), 0);
+    }
+
+    #[test]
+    fn test_entry_ref_and_replace_entry_with() {
+        let mut a = HashMap::new();
+
+        let key = "a key";
+        let value = "an initial value";
+        let new_value = "a new value";
+
+        let entry = a.entry_ref(key).and_replace_entry_with(|_, _| panic!());
+
+        match entry {
+            EntryRef::Vacant(e) => assert_eq!(e.key(), key),
+            EntryRef::Occupied(_) => panic!(),
+        }
+
+        a.insert(key.to_owned(), value);
+
+        let entry = a.entry_ref(key).and_replace_entry_with(|k, v| {
+            assert_eq!(k, key);
+            assert_eq!(v, value);
+            Some(new_value)
+        });
+
+        match entry {
+            EntryRef::Occupied(e) => {
+                assert_eq!(e.key(), key);
+                assert_eq!(e.get(), &new_value);
+            }
+            EntryRef::Vacant(_) => panic!(),
+        }
+
+        assert_eq!(a[key], new_value);
+        assert_eq!(a.len(), 1);
+
+        let entry = a.entry_ref(key).and_replace_entry_with(|k, v| {
+            assert_eq!(k, key);
+            assert_eq!(v, new_value);
+            None
+        });
+
+        match entry {
+            EntryRef::Vacant(e) => assert_eq!(e.key(), key),
+            EntryRef::Occupied(_) => panic!(),
+        }
+
+        assert!(!a.contains_key(key));
+        assert_eq!(a.len(), 0);
+    }
+
+    #[test]
+    fn test_raw_occupied_entry_replace_entry_with() {
+        let mut a = HashMap::new();
+
+        let key = "a key";
+        let value = "an initial value";
+        let new_value = "a new value";
+
+        let entry = a
+            .raw_entry_mut()
+            .from_key(&key)
+            .insert(key, value)
+            .replace_entry_with(|k, v| {
+                assert_eq!(k, &key);
+                assert_eq!(v, value);
+                Some(new_value)
+            });
+
+        match entry {
+            RawEntryMut::Occupied(e) => {
+                assert_eq!(e.key(), &key);
+                assert_eq!(e.get(), &new_value);
+            }
+            RawEntryMut::Vacant(_) => panic!(),
+        }
+
+        assert_eq!(a[key], new_value);
+        assert_eq!(a.len(), 1);
+
+        let entry = match a.raw_entry_mut().from_key(&key) {
+            RawEntryMut::Occupied(e) => e.replace_entry_with(|k, v| {
+                assert_eq!(k, &key);
+                assert_eq!(v, new_value);
+                None
+            }),
+            RawEntryMut::Vacant(_) => panic!(),
+        };
+
+        match entry {
+            RawEntryMut::Vacant(_) => {}
+            RawEntryMut::Occupied(_) => panic!(),
+        }
+
+        assert!(!a.contains_key(key));
+        assert_eq!(a.len(), 0);
+    }
+
+    #[test]
+    fn test_raw_entry_and_replace_entry_with() {
+        let mut a = HashMap::new();
+
+        let key = "a key";
+        let value = "an initial value";
+        let new_value = "a new value";
+
+        let entry = a
+            .raw_entry_mut()
+            .from_key(&key)
+            .and_replace_entry_with(|_, _| panic!());
+
+        match entry {
+            RawEntryMut::Vacant(_) => {}
+            RawEntryMut::Occupied(_) => panic!(),
+        }
+
+        a.insert(key, value);
+
+        let entry = a
+            .raw_entry_mut()
+            .from_key(&key)
+            .and_replace_entry_with(|k, v| {
+                assert_eq!(k, &key);
+                assert_eq!(v, value);
+                Some(new_value)
+            });
+
+        match entry {
+            RawEntryMut::Occupied(e) => {
+                assert_eq!(e.key(), &key);
+                assert_eq!(e.get(), &new_value);
+            }
+            RawEntryMut::Vacant(_) => panic!(),
+        }
+
+        assert_eq!(a[key], new_value);
+        assert_eq!(a.len(), 1);
+
+        let entry = a
+            .raw_entry_mut()
+            .from_key(&key)
+            .and_replace_entry_with(|k, v| {
+                assert_eq!(k, &key);
+                assert_eq!(v, new_value);
+                None
+            });
+
+        match entry {
+            RawEntryMut::Vacant(_) => {}
+            RawEntryMut::Occupied(_) => panic!(),
+        }
+
+        assert!(!a.contains_key(key));
+        assert_eq!(a.len(), 0);
+    }
+
+    #[test]
+    fn test_replace_entry_with_doesnt_corrupt() {
+        #![allow(deprecated)] //rand
+                              // Test for #19292
+        fn check(m: &HashMap<i32, ()>) {
+            for k in m.keys() {
+                assert!(m.contains_key(k), "{} is in keys() but not in the map?", k);
+            }
+        }
+
+        let mut m = HashMap::new();
+
+        let mut rng = {
+            let seed = u64::from_le_bytes(*b"testseed");
+            SmallRng::seed_from_u64(seed)
+        };
+
+        // Populate the map with some items.
+        for _ in 0..50 {
+            let x = rng.gen_range(-10..10);
+            m.insert(x, ());
+        }
+
+        for _ in 0..1000 {
+            let x = rng.gen_range(-10..10);
+            m.entry(x).and_replace_entry_with(|_, _| None);
+            check(&m);
+        }
+    }
+
+    #[test]
+    fn test_replace_entry_ref_with_doesnt_corrupt() {
+        #![allow(deprecated)] //rand
+                              // Test for #19292
+        fn check(m: &HashMap<std::string::String, ()>) {
+            for k in m.keys() {
+                assert!(m.contains_key(k), "{} is in keys() but not in the map?", k);
+            }
+        }
+
+        let mut m = HashMap::new();
+
+        let mut rng = {
+            let seed = u64::from_le_bytes(*b"testseed");
+            SmallRng::seed_from_u64(seed)
+        };
+
+        // Populate the map with some items.
+        for _ in 0..50 {
+            let mut x = std::string::String::with_capacity(1);
+            x.push(rng.gen_range('a'..='z'));
+            m.insert(x, ());
+        }
+
+        for _ in 0..1000 {
+            let mut x = std::string::String::with_capacity(1);
+            x.push(rng.gen_range('a'..='z'));
+            m.entry_ref(x.as_str()).and_replace_entry_with(|_, _| None);
+            check(&m);
+        }
+    }
+
+    #[test]
+    fn test_retain() {
+        let mut map: HashMap<i32, i32> = (0..100).map(|x| (x, x * 10)).collect();
+
+        map.retain(|&k, _| k % 2 == 0);
+        assert_eq!(map.len(), 50);
+        assert_eq!(map[&2], 20);
+        assert_eq!(map[&4], 40);
+        assert_eq!(map[&6], 60);
+    }
+
+    #[test]
+    fn test_drain_filter() {
+        {
+            let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x * 10)).collect();
+            let drained = map.drain_filter(|&k, _| k % 2 == 0);
+            let mut out = drained.collect::<Vec<_>>();
+            out.sort_unstable();
+            assert_eq!(vec![(0, 0), (2, 20), (4, 40), (6, 60)], out);
+            assert_eq!(map.len(), 4);
+        }
+        {
+            let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x * 10)).collect();
+            drop(map.drain_filter(|&k, _| k % 2 == 0));
+            assert_eq!(map.len(), 4);
+        }
+    }
+
+    #[test]
+    #[cfg_attr(miri, ignore)] // FIXME: no OOM signalling (https://github.com/rust-lang/miri/issues/613)
+    fn test_try_reserve() {
+        use crate::TryReserveError::{AllocError, CapacityOverflow};
+
+        const MAX_USIZE: usize = usize::MAX;
+
+        let mut empty_bytes: HashMap<u8, u8> = HashMap::new();
+
+        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE) {
+        } else {
+            panic!("usize::MAX should trigger an overflow!");
+        }
+
+        if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE / 16) {
+        } else {
+            // This may succeed if there is enough free memory. Attempt to
+            // allocate a few more hashmaps to ensure the allocation will fail.
+            let mut empty_bytes2: HashMap<u8, u8> = HashMap::new();
+            let _ = empty_bytes2.try_reserve(MAX_USIZE / 16);
+            let mut empty_bytes3: HashMap<u8, u8> = HashMap::new();
+            let _ = empty_bytes3.try_reserve(MAX_USIZE / 16);
+            let mut empty_bytes4: HashMap<u8, u8> = HashMap::new();
+            if let Err(AllocError { .. }) = empty_bytes4.try_reserve(MAX_USIZE / 16) {
+            } else {
+                panic!("usize::MAX / 8 should trigger an OOM!");
+            }
+        }
+    }
+
+    #[test]
+    fn test_raw_entry() {
+        use super::RawEntryMut::{Occupied, Vacant};
+
+        let xs = [(1_i32, 10_i32), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)];
+
+        let mut map: HashMap<_, _> = xs.iter().copied().collect();
+
+        let compute_hash = |map: &HashMap<i32, i32>, k: i32| -> u64 {
+            super::make_insert_hash::<i32, _>(map.hasher(), &k)
+        };
+
+        // Existing key (insert)
+        match map.raw_entry_mut().from_key(&1) {
+            Vacant(_) => unreachable!(),
+            Occupied(mut view) => {
+                assert_eq!(view.get(), &10);
+                assert_eq!(view.insert(100), 10);
+            }
+        }
+        let hash1 = compute_hash(&map, 1);
+        assert_eq!(map.raw_entry().from_key(&1).unwrap(), (&1, &100));
+        assert_eq!(
+            map.raw_entry().from_hash(hash1, |k| *k == 1).unwrap(),
+            (&1, &100)
+        );
+        assert_eq!(
+            map.raw_entry().from_key_hashed_nocheck(hash1, &1).unwrap(),
+            (&1, &100)
+        );
+        assert_eq!(map.len(), 6);
+
+        // Existing key (update)
+        match map.raw_entry_mut().from_key(&2) {
+            Vacant(_) => unreachable!(),
+            Occupied(mut view) => {
+                let v = view.get_mut();
+                let new_v = (*v) * 10;
+                *v = new_v;
+            }
+        }
+        let hash2 = compute_hash(&map, 2);
+        assert_eq!(map.raw_entry().from_key(&2).unwrap(), (&2, &200));
+        assert_eq!(
+            map.raw_entry().from_hash(hash2, |k| *k == 2).unwrap(),
+            (&2, &200)
+        );
+        assert_eq!(
+            map.raw_entry().from_key_hashed_nocheck(hash2, &2).unwrap(),
+            (&2, &200)
+        );
+        assert_eq!(map.len(), 6);
+
+        // Existing key (take)
+        let hash3 = compute_hash(&map, 3);
+        match map.raw_entry_mut().from_key_hashed_nocheck(hash3, &3) {
+            Vacant(_) => unreachable!(),
+            Occupied(view) => {
+                assert_eq!(view.remove_entry(), (3, 30));
+            }
+        }
+        assert_eq!(map.raw_entry().from_key(&3), None);
+        assert_eq!(map.raw_entry().from_hash(hash3, |k| *k == 3), None);
+        assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash3, &3), None);
+        assert_eq!(map.len(), 5);
+
+        // Nonexistent key (insert)
+        match map.raw_entry_mut().from_key(&10) {
+            Occupied(_) => unreachable!(),
+            Vacant(view) => {
+                assert_eq!(view.insert(10, 1000), (&mut 10, &mut 1000));
+            }
+        }
+        assert_eq!(map.raw_entry().from_key(&10).unwrap(), (&10, &1000));
+        assert_eq!(map.len(), 6);
+
+        // Ensure all lookup methods produce equivalent results.
+        for k in 0..12 {
+            let hash = compute_hash(&map, k);
+            let v = map.get(&k).copied();
+            let kv = v.as_ref().map(|v| (&k, v));
+
+            assert_eq!(map.raw_entry().from_key(&k), kv);
+            assert_eq!(map.raw_entry().from_hash(hash, |q| *q == k), kv);
+            assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash, &k), kv);
+
+            match map.raw_entry_mut().from_key(&k) {
+                Occupied(o) => assert_eq!(Some(o.get_key_value()), kv),
+                Vacant(_) => assert_eq!(v, None),
+            }
+            match map.raw_entry_mut().from_key_hashed_nocheck(hash, &k) {
+                Occupied(o) => assert_eq!(Some(o.get_key_value()), kv),
+                Vacant(_) => assert_eq!(v, None),
+            }
+            match map.raw_entry_mut().from_hash(hash, |q| *q == k) {
+                Occupied(o) => assert_eq!(Some(o.get_key_value()), kv),
+                Vacant(_) => assert_eq!(v, None),
+            }
+        }
+    }
+
+    #[test]
+    fn test_key_without_hash_impl() {
+        #[derive(Debug)]
+        struct IntWrapper(u64);
+
+        let mut m: HashMap<IntWrapper, (), ()> = HashMap::default();
+        {
+            assert!(m.raw_entry().from_hash(0, |k| k.0 == 0).is_none());
+        }
+        {
+            let vacant_entry = match m.raw_entry_mut().from_hash(0, |k| k.0 == 0) {
+                RawEntryMut::Occupied(..) => panic!("Found entry for key 0"),
+                RawEntryMut::Vacant(e) => e,
+            };
+            vacant_entry.insert_with_hasher(0, IntWrapper(0), (), |k| k.0);
+        }
+        {
+            assert!(m.raw_entry().from_hash(0, |k| k.0 == 0).is_some());
+            assert!(m.raw_entry().from_hash(1, |k| k.0 == 1).is_none());
+            assert!(m.raw_entry().from_hash(2, |k| k.0 == 2).is_none());
+        }
+        {
+            let vacant_entry = match m.raw_entry_mut().from_hash(1, |k| k.0 == 1) {
+                RawEntryMut::Occupied(..) => panic!("Found entry for key 1"),
+                RawEntryMut::Vacant(e) => e,
+            };
+            vacant_entry.insert_with_hasher(1, IntWrapper(1), (), |k| k.0);
+        }
+        {
+            assert!(m.raw_entry().from_hash(0, |k| k.0 == 0).is_some());
+            assert!(m.raw_entry().from_hash(1, |k| k.0 == 1).is_some());
+            assert!(m.raw_entry().from_hash(2, |k| k.0 == 2).is_none());
+        }
+        {
+            let occupied_entry = match m.raw_entry_mut().from_hash(0, |k| k.0 == 0) {
+                RawEntryMut::Occupied(e) => e,
+                RawEntryMut::Vacant(..) => panic!("Couldn't find entry for key 0"),
+            };
+            occupied_entry.remove();
+        }
+        assert!(m.raw_entry().from_hash(0, |k| k.0 == 0).is_none());
+        assert!(m.raw_entry().from_hash(1, |k| k.0 == 1).is_some());
+        assert!(m.raw_entry().from_hash(2, |k| k.0 == 2).is_none());
+    }
+
+    #[test]
+    #[cfg(feature = "raw")]
+    fn test_into_iter_refresh() {
+        #[cfg(miri)]
+        const N: usize = 32;
+        #[cfg(not(miri))]
+        const N: usize = 128;
+
+        let mut rng = rand::thread_rng();
+        for n in 0..N {
+            let mut map = HashMap::new();
+            for i in 0..n {
+                assert!(map.insert(i, 2 * i).is_none());
+            }
+            let hash_builder = map.hasher().clone();
+
+            let mut it = unsafe { map.table.iter() };
+            assert_eq!(it.len(), n);
+
+            let mut i = 0;
+            let mut left = n;
+            let mut removed = Vec::new();
+            loop {
+                // occasionally remove some elements
+                if i < n && rng.gen_bool(0.1) {
+                    let hash_value = super::make_insert_hash(&hash_builder, &i);
+
+                    unsafe {
+                        let e = map.table.find(hash_value, |q| q.0.eq(&i));
+                        if let Some(e) = e {
+                            it.reflect_remove(&e);
+                            let t = map.table.remove(e);
+                            removed.push(t);
+                            left -= 1;
+                        } else {
+                            assert!(removed.contains(&(i, 2 * i)), "{} not in {:?}", i, removed);
+                            let e = map.table.insert(
+                                hash_value,
+                                (i, 2 * i),
+                                super::make_hasher::<usize, _, usize, _>(&hash_builder),
+                            );
+                            it.reflect_insert(&e);
+                            if let Some(p) = removed.iter().position(|e| e == &(i, 2 * i)) {
+                                removed.swap_remove(p);
+                            }
+                            left += 1;
+                        }
+                    }
+                }
+
+                let e = it.next();
+                if e.is_none() {
+                    break;
+                }
+                assert!(i < n);
+                let t = unsafe { e.unwrap().as_ref() };
+                assert!(!removed.contains(t));
+                let (key, value) = t;
+                assert_eq!(*value, 2 * key);
+                i += 1;
+            }
+            assert!(i <= n);
+
+            // just for safety:
+            assert_eq!(map.table.len(), left);
+        }
+    }
+
+    #[test]
+    fn test_const_with_hasher() {
+        use core::hash::BuildHasher;
+        use std::collections::hash_map::DefaultHasher;
+
+        #[derive(Clone)]
+        struct MyHasher;
+        impl BuildHasher for MyHasher {
+            type Hasher = DefaultHasher;
+
+            fn build_hasher(&self) -> DefaultHasher {
+                DefaultHasher::new()
+            }
+        }
+
+        const EMPTY_MAP: HashMap<u32, std::string::String, MyHasher> =
+            HashMap::with_hasher(MyHasher);
+
+        let mut map = EMPTY_MAP;
+        map.insert(17, "seventeen".to_owned());
+        assert_eq!("seventeen", map[&17]);
+    }
+
+    #[test]
+    fn test_get_each_mut() {
+        let mut map = HashMap::new();
+        map.insert("foo".to_owned(), 0);
+        map.insert("bar".to_owned(), 10);
+        map.insert("baz".to_owned(), 20);
+        map.insert("qux".to_owned(), 30);
+
+        let xs = map.get_many_mut(["foo", "qux"]);
+        assert_eq!(xs, Some([&mut 0, &mut 30]));
+
+        let xs = map.get_many_mut(["foo", "dud"]);
+        assert_eq!(xs, None);
+
+        let xs = map.get_many_mut(["foo", "foo"]);
+        assert_eq!(xs, None);
+
+        let ys = map.get_many_key_value_mut(["bar", "baz"]);
+        assert_eq!(
+            ys,
+            Some([(&"bar".to_owned(), &mut 10), (&"baz".to_owned(), &mut 20),]),
+        );
+
+        let ys = map.get_many_key_value_mut(["bar", "dip"]);
+        assert_eq!(ys, None);
+
+        let ys = map.get_many_key_value_mut(["baz", "baz"]);
+        assert_eq!(ys, None);
+    }
+
+    #[test]
+    #[should_panic = "panic in drop"]
+    fn test_clone_from_double_drop() {
+        #[derive(Clone)]
+        struct CheckedDrop {
+            panic_in_drop: bool,
+            dropped: bool,
+        }
+        impl Drop for CheckedDrop {
+            fn drop(&mut self) {
+                if self.panic_in_drop {
+                    self.dropped = true;
+                    panic!("panic in drop");
+                }
+                if self.dropped {
+                    panic!("double drop");
+                }
+                self.dropped = true;
+            }
+        }
+        const DISARMED: CheckedDrop = CheckedDrop {
+            panic_in_drop: false,
+            dropped: false,
+        };
+        const ARMED: CheckedDrop = CheckedDrop {
+            panic_in_drop: true,
+            dropped: false,
+        };
+
+        let mut map1 = HashMap::new();
+        map1.insert(1, DISARMED);
+        map1.insert(2, DISARMED);
+        map1.insert(3, DISARMED);
+        map1.insert(4, DISARMED);
+
+        let mut map2 = HashMap::new();
+        map2.insert(1, DISARMED);
+        map2.insert(2, ARMED);
+        map2.insert(3, DISARMED);
+        map2.insert(4, DISARMED);
+
+        map2.clone_from(&map1);
+    }
+}