Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

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

1 files changed, 2790 insertions, 0 deletions

diff --git a/third_party/rust/hashbrown/src/set.rs b/third_party/rust/hashbrown/src/set.rs
new file mode 100644
index 0000000000..2a4dcea52c
--- /dev/null
+++ b/third_party/rust/hashbrown/src/set.rs
@@ -0,0 +1,2790 @@
+use crate::TryReserveError;
+use alloc::borrow::ToOwned;
+use core::borrow::Borrow;
+use core::fmt;
+use core::hash::{BuildHasher, Hash};
+use core::iter::{Chain, FromIterator, FusedIterator};
+use core::mem;
+use core::ops::{BitAnd, BitOr, BitXor, Sub};
+
+use super::map::{self, ConsumeAllOnDrop, DefaultHashBuilder, DrainFilterInner, HashMap, Keys};
+use crate::raw::{Allocator, Global};
+
+// Future Optimization (FIXME!)
+// =============================
+//
+// Iteration over zero sized values is a noop. There is no need
+// for `bucket.val` in the case of HashSet. I suppose we would need HKT
+// to get rid of it properly.
+
+/// A hash set implemented as a `HashMap` where the value is `()`.
+///
+/// As with the [`HashMap`] type, a `HashSet` requires that the elements
+/// implement the [`Eq`] and [`Hash`] traits. 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 an item to be modified in such a way that the
+/// item's hash, as determined by the [`Hash`] trait, or its equality, as
+/// determined by the [`Eq`] trait, changes while it is in the set. 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 `HashSet` may become corrupted and
+/// some items may be dropped from the table.
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::HashSet;
+/// // Type inference lets us omit an explicit type signature (which
+/// // would be `HashSet<String>` in this example).
+/// let mut books = HashSet::new();
+///
+/// // Add some books.
+/// books.insert("A Dance With Dragons".to_string());
+/// books.insert("To Kill a Mockingbird".to_string());
+/// books.insert("The Odyssey".to_string());
+/// books.insert("The Great Gatsby".to_string());
+///
+/// // Check for a specific one.
+/// if !books.contains("The Winds of Winter") {
+///     println!("We have {} books, but The Winds of Winter ain't one.",
+///              books.len());
+/// }
+///
+/// // Remove a book.
+/// books.remove("The Odyssey");
+///
+/// // Iterate over everything.
+/// for book in &books {
+///     println!("{}", book);
+/// }
+/// ```
+///
+/// The easiest way to use `HashSet` with a custom type is to derive
+/// [`Eq`] and [`Hash`]. We must also derive [`PartialEq`]. This will in the
+/// future be implied by [`Eq`].
+///
+/// ```
+/// use hashbrown::HashSet;
+/// #[derive(Hash, Eq, PartialEq, Debug)]
+/// struct Viking {
+///     name: String,
+///     power: usize,
+/// }
+///
+/// let mut vikings = HashSet::new();
+///
+/// vikings.insert(Viking { name: "Einar".to_string(), power: 9 });
+/// vikings.insert(Viking { name: "Einar".to_string(), power: 9 });
+/// vikings.insert(Viking { name: "Olaf".to_string(), power: 4 });
+/// vikings.insert(Viking { name: "Harald".to_string(), power: 8 });
+///
+/// // Use derived implementation to print the vikings.
+/// for x in &vikings {
+///     println!("{:?}", x);
+/// }
+/// ```
+///
+/// A `HashSet` with fixed list of elements can be initialized from an array:
+///
+/// ```
+/// use hashbrown::HashSet;
+///
+/// let viking_names: HashSet<&'static str> =
+///     [ "Einar", "Olaf", "Harald" ].iter().cloned().collect();
+/// // use the values stored in the set
+/// ```
+///
+/// [`Cell`]: https://doc.rust-lang.org/std/cell/struct.Cell.html
+/// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+/// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+/// [`HashMap`]: struct.HashMap.html
+/// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
+/// [`RefCell`]: https://doc.rust-lang.org/std/cell/struct.RefCell.html
+pub struct HashSet<T, S = DefaultHashBuilder, A: Allocator + Clone = Global> {
+    pub(crate) map: HashMap<T, (), S, A>,
+}
+
+impl<T: Clone, S: Clone, A: Allocator + Clone> Clone for HashSet<T, S, A> {
+    fn clone(&self) -> Self {
+        HashSet {
+            map: self.map.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, source: &Self) {
+        self.map.clone_from(&source.map);
+    }
+}
+
+#[cfg(feature = "ahash")]
+impl<T> HashSet<T, DefaultHashBuilder> {
+    /// Creates an empty `HashSet`.
+    ///
+    /// The hash set is initially created with a capacity of 0, so it will not allocate until it
+    /// is first inserted into.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let set: HashSet<i32> = HashSet::new();
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn new() -> Self {
+        Self {
+            map: HashMap::new(),
+        }
+    }
+
+    /// Creates an empty `HashSet` with the specified capacity.
+    ///
+    /// The hash set will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash set will not allocate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let set: HashSet<i32> = HashSet::with_capacity(10);
+    /// assert!(set.capacity() >= 10);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            map: HashMap::with_capacity(capacity),
+        }
+    }
+}
+
+#[cfg(feature = "ahash")]
+impl<T: Hash + Eq, A: Allocator + Clone> HashSet<T, DefaultHashBuilder, A> {
+    /// Creates an empty `HashSet`.
+    ///
+    /// The hash set is initially created with a capacity of 0, so it will not allocate until it
+    /// is first inserted into.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let set: HashSet<i32> = HashSet::new();
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn new_in(alloc: A) -> Self {
+        Self {
+            map: HashMap::new_in(alloc),
+        }
+    }
+
+    /// Creates an empty `HashSet` with the specified capacity.
+    ///
+    /// The hash set will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash set will not allocate.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let set: HashSet<i32> = HashSet::with_capacity(10);
+    /// assert!(set.capacity() >= 10);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
+        Self {
+            map: HashMap::with_capacity_in(capacity, alloc),
+        }
+    }
+}
+
+impl<T, S, A: Allocator + Clone> HashSet<T, S, A> {
+    /// Returns the number of elements the set can hold without reallocating.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let set: HashSet<i32> = HashSet::with_capacity(100);
+    /// assert!(set.capacity() >= 100);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn capacity(&self) -> usize {
+        self.map.capacity()
+    }
+
+    /// An iterator visiting all elements in arbitrary order.
+    /// The iterator element type is `&'a T`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let mut set = HashSet::new();
+    /// set.insert("a");
+    /// set.insert("b");
+    ///
+    /// // Will print in an arbitrary order.
+    /// for x in set.iter() {
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn iter(&self) -> Iter<'_, T> {
+        Iter {
+            iter: self.map.keys(),
+        }
+    }
+
+    /// Returns the number of elements in the set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut v = HashSet::new();
+    /// assert_eq!(v.len(), 0);
+    /// v.insert(1);
+    /// assert_eq!(v.len(), 1);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn len(&self) -> usize {
+        self.map.len()
+    }
+
+    /// Returns `true` if the set contains no elements.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut v = HashSet::new();
+    /// assert!(v.is_empty());
+    /// v.insert(1);
+    /// assert!(!v.is_empty());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn is_empty(&self) -> bool {
+        self.map.is_empty()
+    }
+
+    /// Clears the set, returning all elements in an iterator.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert!(!set.is_empty());
+    ///
+    /// // print 1, 2, 3 in an arbitrary order
+    /// for i in set.drain() {
+    ///     println!("{}", i);
+    /// }
+    ///
+    /// assert!(set.is_empty());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn drain(&mut self) -> Drain<'_, T, A> {
+        Drain {
+            iter: self.map.drain(),
+        }
+    }
+
+    /// Retains only the elements specified by the predicate.
+    ///
+    /// In other words, remove all elements `e` such that `f(&e)` returns `false`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let xs = [1,2,3,4,5,6];
+    /// let mut set: HashSet<i32> = xs.iter().cloned().collect();
+    /// set.retain(|&k| k % 2 == 0);
+    /// assert_eq!(set.len(), 3);
+    /// ```
+    pub fn retain<F>(&mut self, mut f: F)
+    where
+        F: FnMut(&T) -> bool,
+    {
+        self.map.retain(|k, _| f(k));
+    }
+
+    /// Drains elements which are true under the given predicate,
+    /// and returns an iterator over the removed items.
+    ///
+    /// In other words, move all elements `e` such that `f(&e)` returns `true` out
+    /// into another iterator.
+    ///
+    /// When the returned DrainedFilter is dropped, any remaining elements that satisfy
+    /// the predicate are dropped from the set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<i32> = (0..8).collect();
+    /// let drained: HashSet<i32> = set.drain_filter(|v| v % 2 == 0).collect();
+    ///
+    /// let mut evens = drained.into_iter().collect::<Vec<_>>();
+    /// let mut odds = set.into_iter().collect::<Vec<_>>();
+    /// evens.sort();
+    /// odds.sort();
+    ///
+    /// assert_eq!(evens, vec![0, 2, 4, 6]);
+    /// assert_eq!(odds, vec![1, 3, 5, 7]);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn drain_filter<F>(&mut self, f: F) -> DrainFilter<'_, T, F, A>
+    where
+        F: FnMut(&T) -> bool,
+    {
+        DrainFilter {
+            f,
+            inner: DrainFilterInner {
+                iter: unsafe { self.map.table.iter() },
+                table: &mut self.map.table,
+            },
+        }
+    }
+
+    /// Clears the set, removing all values.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut v = HashSet::new();
+    /// v.insert(1);
+    /// v.clear();
+    /// assert!(v.is_empty());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn clear(&mut self) {
+        self.map.clear();
+    }
+}
+
+impl<T, S> HashSet<T, S, Global> {
+    /// Creates a new empty hash set which will use the given hasher to hash
+    /// keys.
+    ///
+    /// The hash set is also created with the default initial capacity.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow `HashSet`s 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::HashSet;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut set = HashSet::with_hasher(s);
+    /// set.insert(2);
+    /// ```
+    ///
+    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub const fn with_hasher(hasher: S) -> Self {
+        Self {
+            map: HashMap::with_hasher(hasher),
+        }
+    }
+
+    /// Creates an empty `HashSet` with the specified capacity, using
+    /// `hasher` to hash the keys.
+    ///
+    /// The hash set will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash set will not allocate.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow `HashSet`s 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::HashSet;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut set = HashSet::with_capacity_and_hasher(10, s);
+    /// set.insert(1);
+    /// ```
+    ///
+    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> Self {
+        Self {
+            map: HashMap::with_capacity_and_hasher(capacity, hasher),
+        }
+    }
+}
+
+impl<T, S, A> HashSet<T, S, A>
+where
+    A: Allocator + Clone,
+{
+    /// Returns a reference to the underlying allocator.
+    #[inline]
+    pub fn allocator(&self) -> &A {
+        self.map.allocator()
+    }
+
+    /// Creates a new empty hash set which will use the given hasher to hash
+    /// keys.
+    ///
+    /// The hash set is also created with the default initial capacity.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow `HashSet`s 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::HashSet;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut set = HashSet::with_hasher(s);
+    /// set.insert(2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_hasher_in(hasher: S, alloc: A) -> Self {
+        Self {
+            map: HashMap::with_hasher_in(hasher, alloc),
+        }
+    }
+
+    /// Creates an empty `HashSet` with the specified capacity, using
+    /// `hasher` to hash the keys.
+    ///
+    /// The hash set will be able to hold at least `capacity` elements without
+    /// reallocating. If `capacity` is 0, the hash set will not allocate.
+    ///
+    /// Warning: `hasher` is normally randomly generated, and
+    /// is designed to allow `HashSet`s 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::HashSet;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let s = DefaultHashBuilder::default();
+    /// let mut set = HashSet::with_capacity_and_hasher(10, s);
+    /// set.insert(1);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn with_capacity_and_hasher_in(capacity: usize, hasher: S, alloc: A) -> Self {
+        Self {
+            map: HashMap::with_capacity_and_hasher_in(capacity, hasher, alloc),
+        }
+    }
+
+    /// Returns a reference to the set's [`BuildHasher`].
+    ///
+    /// [`BuildHasher`]: https://doc.rust-lang.org/std/hash/trait.BuildHasher.html
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// use hashbrown::hash_map::DefaultHashBuilder;
+    ///
+    /// let hasher = DefaultHashBuilder::default();
+    /// let set: HashSet<i32> = HashSet::with_hasher(hasher);
+    /// let hasher: &DefaultHashBuilder = set.hasher();
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn hasher(&self) -> &S {
+        self.map.hasher()
+    }
+}
+
+impl<T, S, A> HashSet<T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    /// Reserves capacity for at least `additional` more elements to be inserted
+    /// in the `HashSet`. The collection may reserve more space to avoid
+    /// frequent reallocations.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the new allocation size overflows `usize`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let mut set: HashSet<i32> = HashSet::new();
+    /// set.reserve(10);
+    /// assert!(set.capacity() >= 10);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn reserve(&mut self, additional: usize) {
+        self.map.reserve(additional);
+    }
+
+    /// Tries to reserve capacity for at least `additional` more elements to be inserted
+    /// in the given `HashSet<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::HashSet;
+    /// let mut set: HashSet<i32> = HashSet::new();
+    /// set.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
+        self.map.try_reserve(additional)
+    }
+
+    /// Shrinks the capacity of the set 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::HashSet;
+    ///
+    /// let mut set = HashSet::with_capacity(100);
+    /// set.insert(1);
+    /// set.insert(2);
+    /// assert!(set.capacity() >= 100);
+    /// set.shrink_to_fit();
+    /// assert!(set.capacity() >= 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn shrink_to_fit(&mut self) {
+        self.map.shrink_to_fit();
+    }
+
+    /// Shrinks the capacity of the set 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.
+    ///
+    /// Panics if the current capacity is smaller than the supplied
+    /// minimum capacity.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set = HashSet::with_capacity(100);
+    /// set.insert(1);
+    /// set.insert(2);
+    /// assert!(set.capacity() >= 100);
+    /// set.shrink_to(10);
+    /// assert!(set.capacity() >= 10);
+    /// set.shrink_to(0);
+    /// assert!(set.capacity() >= 2);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn shrink_to(&mut self, min_capacity: usize) {
+        self.map.shrink_to(min_capacity);
+    }
+
+    /// Visits the values representing the difference,
+    /// i.e., the values that are in `self` but not in `other`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Can be seen as `a - b`.
+    /// for x in a.difference(&b) {
+    ///     println!("{}", x); // Print 1
+    /// }
+    ///
+    /// let diff: HashSet<_> = a.difference(&b).collect();
+    /// assert_eq!(diff, [1].iter().collect());
+    ///
+    /// // Note that difference is not symmetric,
+    /// // and `b - a` means something else:
+    /// let diff: HashSet<_> = b.difference(&a).collect();
+    /// assert_eq!(diff, [4].iter().collect());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn difference<'a>(&'a self, other: &'a Self) -> Difference<'a, T, S, A> {
+        Difference {
+            iter: self.iter(),
+            other,
+        }
+    }
+
+    /// Visits the values representing the symmetric difference,
+    /// i.e., the values that are in `self` or in `other` but not in both.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Print 1, 4 in arbitrary order.
+    /// for x in a.symmetric_difference(&b) {
+    ///     println!("{}", x);
+    /// }
+    ///
+    /// let diff1: HashSet<_> = a.symmetric_difference(&b).collect();
+    /// let diff2: HashSet<_> = b.symmetric_difference(&a).collect();
+    ///
+    /// assert_eq!(diff1, diff2);
+    /// assert_eq!(diff1, [1, 4].iter().collect());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn symmetric_difference<'a>(&'a self, other: &'a Self) -> SymmetricDifference<'a, T, S, A> {
+        SymmetricDifference {
+            iter: self.difference(other).chain(other.difference(self)),
+        }
+    }
+
+    /// Visits the values representing the intersection,
+    /// i.e., the values that are both in `self` and `other`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Print 2, 3 in arbitrary order.
+    /// for x in a.intersection(&b) {
+    ///     println!("{}", x);
+    /// }
+    ///
+    /// let intersection: HashSet<_> = a.intersection(&b).collect();
+    /// assert_eq!(intersection, [2, 3].iter().collect());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn intersection<'a>(&'a self, other: &'a Self) -> Intersection<'a, T, S, A> {
+        let (smaller, larger) = if self.len() <= other.len() {
+            (self, other)
+        } else {
+            (other, self)
+        };
+        Intersection {
+            iter: smaller.iter(),
+            other: larger,
+        }
+    }
+
+    /// Visits the values representing the union,
+    /// i.e., all the values in `self` or `other`, without duplicates.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let b: HashSet<_> = [4, 2, 3, 4].iter().cloned().collect();
+    ///
+    /// // Print 1, 2, 3, 4 in arbitrary order.
+    /// for x in a.union(&b) {
+    ///     println!("{}", x);
+    /// }
+    ///
+    /// let union: HashSet<_> = a.union(&b).collect();
+    /// assert_eq!(union, [1, 2, 3, 4].iter().collect());
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn union<'a>(&'a self, other: &'a Self) -> Union<'a, T, S, A> {
+        // We'll iterate one set in full, and only the remaining difference from the other.
+        // Use the smaller set for the difference in order to reduce hash lookups.
+        let (smaller, larger) = if self.len() <= other.len() {
+            (self, other)
+        } else {
+            (other, self)
+        };
+        Union {
+            iter: larger.iter().chain(smaller.difference(larger)),
+        }
+    }
+
+    /// Returns `true` if the set contains a value.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the value type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert_eq!(set.contains(&1), true);
+    /// assert_eq!(set.contains(&4), false);
+    /// ```
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn contains<Q: ?Sized>(&self, value: &Q) -> bool
+    where
+        T: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.map.contains_key(value)
+    }
+
+    /// Returns a reference to the value in the set, if any, that is equal to the given value.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the value type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert_eq!(set.get(&2), Some(&2));
+    /// assert_eq!(set.get(&4), None);
+    /// ```
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get<Q: ?Sized>(&self, value: &Q) -> Option<&T>
+    where
+        T: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.map.get_key_value(value) {
+            Some((k, _)) => Some(k),
+            None => None,
+        }
+    }
+
+    /// Inserts the given `value` into the set if it is not present, then
+    /// returns a reference to the value in the set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert_eq!(set.len(), 3);
+    /// assert_eq!(set.get_or_insert(2), &2);
+    /// assert_eq!(set.get_or_insert(100), &100);
+    /// assert_eq!(set.len(), 4); // 100 was inserted
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_or_insert(&mut self, value: T) -> &T {
+        // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with
+        // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`.
+        self.map
+            .raw_entry_mut()
+            .from_key(&value)
+            .or_insert(value, ())
+            .0
+    }
+
+    /// Inserts an owned copy of the given `value` into the set if it is not
+    /// present, then returns a reference to the value in the set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<String> = ["cat", "dog", "horse"]
+    ///     .iter().map(|&pet| pet.to_owned()).collect();
+    ///
+    /// assert_eq!(set.len(), 3);
+    /// for &pet in &["cat", "dog", "fish"] {
+    ///     let value = set.get_or_insert_owned(pet);
+    ///     assert_eq!(value, pet);
+    /// }
+    /// assert_eq!(set.len(), 4); // a new "fish" was inserted
+    /// ```
+    #[inline]
+    pub fn get_or_insert_owned<Q: ?Sized>(&mut self, value: &Q) -> &T
+    where
+        T: Borrow<Q>,
+        Q: Hash + Eq + ToOwned<Owned = T>,
+    {
+        // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with
+        // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`.
+        self.map
+            .raw_entry_mut()
+            .from_key(value)
+            .or_insert_with(|| (value.to_owned(), ()))
+            .0
+    }
+
+    /// Inserts a value computed from `f` into the set if the given `value` is
+    /// not present, then returns a reference to the value in the set.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<String> = ["cat", "dog", "horse"]
+    ///     .iter().map(|&pet| pet.to_owned()).collect();
+    ///
+    /// assert_eq!(set.len(), 3);
+    /// for &pet in &["cat", "dog", "fish"] {
+    ///     let value = set.get_or_insert_with(pet, str::to_owned);
+    ///     assert_eq!(value, pet);
+    /// }
+    /// assert_eq!(set.len(), 4); // a new "fish" was inserted
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get_or_insert_with<Q: ?Sized, F>(&mut self, value: &Q, f: F) -> &T
+    where
+        T: Borrow<Q>,
+        Q: Hash + Eq,
+        F: FnOnce(&Q) -> T,
+    {
+        // Although the raw entry gives us `&mut T`, we only return `&T` to be consistent with
+        // `get`. Key mutation is "raw" because you're not supposed to affect `Eq` or `Hash`.
+        self.map
+            .raw_entry_mut()
+            .from_key(value)
+            .or_insert_with(|| (f(value), ()))
+            .0
+    }
+
+    /// Gets the given value's corresponding entry in the set for in-place manipulation.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// use hashbrown::hash_set::Entry::*;
+    ///
+    /// let mut singles = HashSet::new();
+    /// let mut dupes = HashSet::new();
+    ///
+    /// for ch in "a short treatise on fungi".chars() {
+    ///     if let Vacant(dupe_entry) = dupes.entry(ch) {
+    ///         // We haven't already seen a duplicate, so
+    ///         // check if we've at least seen it once.
+    ///         match singles.entry(ch) {
+    ///             Vacant(single_entry) => {
+    ///                 // We found a new character for the first time.
+    ///                 single_entry.insert()
+    ///             }
+    ///             Occupied(single_entry) => {
+    ///                 // We've already seen this once, "move" it to dupes.
+    ///                 single_entry.remove();
+    ///                 dupe_entry.insert();
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    ///
+    /// assert!(!singles.contains(&'t') && dupes.contains(&'t'));
+    /// assert!(singles.contains(&'u') && !dupes.contains(&'u'));
+    /// assert!(!singles.contains(&'v') && !dupes.contains(&'v'));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn entry(&mut self, value: T) -> Entry<'_, T, S, A> {
+        match self.map.entry(value) {
+            map::Entry::Occupied(entry) => Entry::Occupied(OccupiedEntry { inner: entry }),
+            map::Entry::Vacant(entry) => Entry::Vacant(VacantEntry { inner: entry }),
+        }
+    }
+
+    /// Returns `true` if `self` has no elements in common with `other`.
+    /// This is equivalent to checking for an empty intersection.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let a: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let mut b = HashSet::new();
+    ///
+    /// assert_eq!(a.is_disjoint(&b), true);
+    /// b.insert(4);
+    /// assert_eq!(a.is_disjoint(&b), true);
+    /// b.insert(1);
+    /// assert_eq!(a.is_disjoint(&b), false);
+    /// ```
+    pub fn is_disjoint(&self, other: &Self) -> bool {
+        self.iter().all(|v| !other.contains(v))
+    }
+
+    /// Returns `true` if the set is a subset of another,
+    /// i.e., `other` contains at least all the values in `self`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let sup: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// let mut set = HashSet::new();
+    ///
+    /// assert_eq!(set.is_subset(&sup), true);
+    /// set.insert(2);
+    /// assert_eq!(set.is_subset(&sup), true);
+    /// set.insert(4);
+    /// assert_eq!(set.is_subset(&sup), false);
+    /// ```
+    pub fn is_subset(&self, other: &Self) -> bool {
+        self.len() <= other.len() && self.iter().all(|v| other.contains(v))
+    }
+
+    /// Returns `true` if the set is a superset of another,
+    /// i.e., `self` contains at least all the values in `other`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let sub: HashSet<_> = [1, 2].iter().cloned().collect();
+    /// let mut set = HashSet::new();
+    ///
+    /// assert_eq!(set.is_superset(&sub), false);
+    ///
+    /// set.insert(0);
+    /// set.insert(1);
+    /// assert_eq!(set.is_superset(&sub), false);
+    ///
+    /// set.insert(2);
+    /// assert_eq!(set.is_superset(&sub), true);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn is_superset(&self, other: &Self) -> bool {
+        other.is_subset(self)
+    }
+
+    /// Adds a value to the set.
+    ///
+    /// If the set did not have this value present, `true` is returned.
+    ///
+    /// If the set did have this value present, `false` is returned.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set = HashSet::new();
+    ///
+    /// assert_eq!(set.insert(2), true);
+    /// assert_eq!(set.insert(2), false);
+    /// assert_eq!(set.len(), 1);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(&mut self, value: T) -> bool {
+        self.map.insert(value, ()).is_none()
+    }
+
+    /// Insert a value the set without checking if the value already exists in the set.
+    ///
+    /// Returns a reference to the value just inserted.
+    ///
+    /// This operation is safe if a value does not exist in the set.
+    ///
+    /// However, if a value exists in the set already, the behavior is unspecified:
+    /// this operation may panic, loop forever, or any following operation with the set
+    /// 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 set.
+    /// For example, when constructing a set from another set, we know
+    /// that values are unique.
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert_unique_unchecked(&mut self, value: T) -> &T {
+        self.map.insert_unique_unchecked(value, ()).0
+    }
+
+    /// Adds a value to the set, replacing the existing value, if any, that is equal to the given
+    /// one. Returns the replaced value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set = HashSet::new();
+    /// set.insert(Vec::<i32>::new());
+    ///
+    /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 0);
+    /// set.replace(Vec::with_capacity(10));
+    /// assert_eq!(set.get(&[][..]).unwrap().capacity(), 10);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace(&mut self, value: T) -> Option<T> {
+        match self.map.entry(value) {
+            map::Entry::Occupied(occupied) => Some(occupied.replace_key()),
+            map::Entry::Vacant(vacant) => {
+                vacant.insert(());
+                None
+            }
+        }
+    }
+
+    /// Removes a value from the set. Returns whether the value was
+    /// present in the set.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the value type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set = HashSet::new();
+    ///
+    /// set.insert(2);
+    /// assert_eq!(set.remove(&2), true);
+    /// assert_eq!(set.remove(&2), false);
+    /// ```
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove<Q: ?Sized>(&mut self, value: &Q) -> bool
+    where
+        T: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.map.remove(value).is_some()
+    }
+
+    /// Removes and returns the value in the set, if any, that is equal to the given one.
+    ///
+    /// The value may be any borrowed form of the set's value type, but
+    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
+    /// the value type.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<_> = [1, 2, 3].iter().cloned().collect();
+    /// assert_eq!(set.take(&2), Some(2));
+    /// assert_eq!(set.take(&2), None);
+    /// ```
+    ///
+    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
+    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn take<Q: ?Sized>(&mut self, value: &Q) -> Option<T>
+    where
+        T: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.map.remove_entry(value) {
+            Some((k, _)) => Some(k),
+            None => None,
+        }
+    }
+}
+
+impl<T, S, A> PartialEq for HashSet<T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    fn eq(&self, other: &Self) -> bool {
+        if self.len() != other.len() {
+            return false;
+        }
+
+        self.iter().all(|key| other.contains(key))
+    }
+}
+
+impl<T, S, A> Eq for HashSet<T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+}
+
+impl<T, S, A> fmt::Debug for HashSet<T, S, A>
+where
+    T: fmt::Debug,
+    A: Allocator + Clone,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_set().entries(self.iter()).finish()
+    }
+}
+
+impl<T, S, A> From<HashMap<T, (), S, A>> for HashSet<T, S, A>
+where
+    A: Allocator + Clone,
+{
+    fn from(map: HashMap<T, (), S, A>) -> Self {
+        Self { map }
+    }
+}
+
+impl<T, S, A> FromIterator<T> for HashSet<T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher + Default,
+    A: Default + Allocator + Clone,
+{
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
+        let mut set = Self::with_hasher_in(Default::default(), Default::default());
+        set.extend(iter);
+        set
+    }
+}
+
+// The default hasher is used to match the std implementation signature
+#[cfg(feature = "ahash")]
+impl<T, A, const N: usize> From<[T; N]> for HashSet<T, DefaultHashBuilder, A>
+where
+    T: Eq + Hash,
+    A: Default + Allocator + Clone,
+{
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let set1 = HashSet::from([1, 2, 3, 4]);
+    /// let set2: HashSet<_> = [1, 2, 3, 4].into();
+    /// assert_eq!(set1, set2);
+    /// ```
+    fn from(arr: [T; N]) -> Self {
+        arr.into_iter().collect()
+    }
+}
+
+impl<T, S, A> Extend<T> for HashSet<T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
+        self.map.extend(iter.into_iter().map(|k| (k, ())));
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_one(&mut self, k: T) {
+        self.map.insert(k, ());
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_reserve(&mut self, additional: usize) {
+        Extend::<(T, ())>::extend_reserve(&mut self.map, additional);
+    }
+}
+
+impl<'a, T, S, A> Extend<&'a T> for HashSet<T, S, A>
+where
+    T: 'a + Eq + Hash + Copy,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn extend<I: IntoIterator<Item = &'a T>>(&mut self, iter: I) {
+        self.extend(iter.into_iter().copied());
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_one(&mut self, k: &'a T) {
+        self.map.insert(*k, ());
+    }
+
+    #[inline]
+    #[cfg(feature = "nightly")]
+    fn extend_reserve(&mut self, additional: usize) {
+        Extend::<(T, ())>::extend_reserve(&mut self.map, additional);
+    }
+}
+
+impl<T, S, A> Default for HashSet<T, S, A>
+where
+    S: Default,
+    A: Default + Allocator + Clone,
+{
+    /// Creates an empty `HashSet<T, S>` with the `Default` value for the hasher.
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn default() -> Self {
+        Self {
+            map: HashMap::default(),
+        }
+    }
+}
+
+impl<T, S, A> BitOr<&HashSet<T, S, A>> for &HashSet<T, S, A>
+where
+    T: Eq + Hash + Clone,
+    S: BuildHasher + Default,
+    A: Allocator + Clone,
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the union of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
+    ///
+    /// let set = &a | &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [1, 2, 3, 4, 5];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn bitor(self, rhs: &HashSet<T, S, A>) -> HashSet<T, S> {
+        self.union(rhs).cloned().collect()
+    }
+}
+
+impl<T, S, A> BitAnd<&HashSet<T, S, A>> for &HashSet<T, S, A>
+where
+    T: Eq + Hash + Clone,
+    S: BuildHasher + Default,
+    A: Allocator + Clone,
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the intersection of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![2, 3, 4].into_iter().collect();
+    ///
+    /// let set = &a & &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [2, 3];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn bitand(self, rhs: &HashSet<T, S, A>) -> HashSet<T, S> {
+        self.intersection(rhs).cloned().collect()
+    }
+}
+
+impl<T, S> BitXor<&HashSet<T, S>> for &HashSet<T, S>
+where
+    T: Eq + Hash + Clone,
+    S: BuildHasher + Default,
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the symmetric difference of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
+    ///
+    /// let set = &a ^ &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [1, 2, 4, 5];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn bitxor(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
+        self.symmetric_difference(rhs).cloned().collect()
+    }
+}
+
+impl<T, S> Sub<&HashSet<T, S>> for &HashSet<T, S>
+where
+    T: Eq + Hash + Clone,
+    S: BuildHasher + Default,
+{
+    type Output = HashSet<T, S>;
+
+    /// Returns the difference of `self` and `rhs` as a new `HashSet<T, S>`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let a: HashSet<_> = vec![1, 2, 3].into_iter().collect();
+    /// let b: HashSet<_> = vec![3, 4, 5].into_iter().collect();
+    ///
+    /// let set = &a - &b;
+    ///
+    /// let mut i = 0;
+    /// let expected = [1, 2];
+    /// for x in &set {
+    ///     assert!(expected.contains(x));
+    ///     i += 1;
+    /// }
+    /// assert_eq!(i, expected.len());
+    /// ```
+    fn sub(self, rhs: &HashSet<T, S>) -> HashSet<T, S> {
+        self.difference(rhs).cloned().collect()
+    }
+}
+
+/// An iterator over the items of a `HashSet`.
+///
+/// This `struct` is created by the [`iter`] method on [`HashSet`].
+/// See its documentation for more.
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`iter`]: struct.HashSet.html#method.iter
+pub struct Iter<'a, K> {
+    iter: Keys<'a, K, ()>,
+}
+
+/// An owning iterator over the items of a `HashSet`.
+///
+/// This `struct` is created by the [`into_iter`] method on [`HashSet`]
+/// (provided by the `IntoIterator` trait). See its documentation for more.
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`into_iter`]: struct.HashSet.html#method.into_iter
+pub struct IntoIter<K, A: Allocator + Clone = Global> {
+    iter: map::IntoIter<K, (), A>,
+}
+
+/// A draining iterator over the items of a `HashSet`.
+///
+/// This `struct` is created by the [`drain`] method on [`HashSet`].
+/// See its documentation for more.
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`drain`]: struct.HashSet.html#method.drain
+pub struct Drain<'a, K, A: Allocator + Clone = Global> {
+    iter: map::Drain<'a, K, (), A>,
+}
+
+/// A draining iterator over entries of a `HashSet` which don't satisfy the predicate `f`.
+///
+/// This `struct` is created by the [`drain_filter`] method on [`HashSet`]. See its
+/// documentation for more.
+///
+/// [`drain_filter`]: struct.HashSet.html#method.drain_filter
+/// [`HashSet`]: struct.HashSet.html
+pub struct DrainFilter<'a, K, F, A: Allocator + Clone = Global>
+where
+    F: FnMut(&K) -> bool,
+{
+    f: F,
+    inner: DrainFilterInner<'a, K, (), A>,
+}
+
+/// A lazy iterator producing elements in the intersection of `HashSet`s.
+///
+/// This `struct` is created by the [`intersection`] method on [`HashSet`].
+/// See its documentation for more.
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`intersection`]: struct.HashSet.html#method.intersection
+pub struct Intersection<'a, T, S, A: Allocator + Clone = Global> {
+    // iterator of the first set
+    iter: Iter<'a, T>,
+    // the second set
+    other: &'a HashSet<T, S, A>,
+}
+
+/// A lazy iterator producing elements in the difference of `HashSet`s.
+///
+/// This `struct` is created by the [`difference`] method on [`HashSet`].
+/// See its documentation for more.
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`difference`]: struct.HashSet.html#method.difference
+pub struct Difference<'a, T, S, A: Allocator + Clone = Global> {
+    // iterator of the first set
+    iter: Iter<'a, T>,
+    // the second set
+    other: &'a HashSet<T, S, A>,
+}
+
+/// A lazy iterator producing elements in the symmetric difference of `HashSet`s.
+///
+/// This `struct` is created by the [`symmetric_difference`] method on
+/// [`HashSet`]. See its documentation for more.
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`symmetric_difference`]: struct.HashSet.html#method.symmetric_difference
+pub struct SymmetricDifference<'a, T, S, A: Allocator + Clone = Global> {
+    iter: Chain<Difference<'a, T, S, A>, Difference<'a, T, S, A>>,
+}
+
+/// A lazy iterator producing elements in the union of `HashSet`s.
+///
+/// This `struct` is created by the [`union`] method on [`HashSet`].
+/// See its documentation for more.
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`union`]: struct.HashSet.html#method.union
+pub struct Union<'a, T, S, A: Allocator + Clone = Global> {
+    iter: Chain<Iter<'a, T>, Difference<'a, T, S, A>>,
+}
+
+impl<'a, T, S, A: Allocator + Clone> IntoIterator for &'a HashSet<T, S, A> {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn into_iter(self) -> Iter<'a, T> {
+        self.iter()
+    }
+}
+
+impl<T, S, A: Allocator + Clone> IntoIterator for HashSet<T, S, A> {
+    type Item = T;
+    type IntoIter = IntoIter<T, A>;
+
+    /// Creates a consuming iterator, that is, one that moves each value out
+    /// of the set in arbitrary order. The set cannot be used after calling
+    /// this.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// let mut set = HashSet::new();
+    /// set.insert("a".to_string());
+    /// set.insert("b".to_string());
+    ///
+    /// // Not possible to collect to a Vec<String> with a regular `.iter()`.
+    /// let v: Vec<String> = set.into_iter().collect();
+    ///
+    /// // Will print in an arbitrary order.
+    /// for x in &v {
+    ///     println!("{}", x);
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn into_iter(self) -> IntoIter<T, A> {
+        IntoIter {
+            iter: self.map.into_iter(),
+        }
+    }
+}
+
+impl<K> Clone for Iter<'_, K> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        Iter {
+            iter: self.iter.clone(),
+        }
+    }
+}
+impl<'a, K> Iterator for Iter<'a, K> {
+    type Item = &'a K;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a K> {
+        self.iter.next()
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+impl<'a, K> ExactSizeIterator for Iter<'a, K> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+impl<K> FusedIterator for Iter<'_, K> {}
+
+impl<K: fmt::Debug> fmt::Debug for Iter<'_, K> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<K, A: Allocator + Clone> Iterator for IntoIter<K, A> {
+    type Item = K;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<K> {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.iter.next() {
+            Some((k, _)) => Some(k),
+            None => None,
+        }
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+impl<K, A: Allocator + Clone> ExactSizeIterator for IntoIter<K, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+impl<K, A: Allocator + Clone> FusedIterator for IntoIter<K, A> {}
+
+impl<K: fmt::Debug, A: Allocator + Clone> fmt::Debug for IntoIter<K, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let entries_iter = self.iter.iter().map(|(k, _)| k);
+        f.debug_list().entries(entries_iter).finish()
+    }
+}
+
+impl<K, A: Allocator + Clone> Iterator for Drain<'_, K, A> {
+    type Item = K;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<K> {
+        // Avoid `Option::map` because it bloats LLVM IR.
+        match self.iter.next() {
+            Some((k, _)) => Some(k),
+            None => None,
+        }
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+impl<K, A: Allocator + Clone> ExactSizeIterator for Drain<'_, K, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+impl<K, A: Allocator + Clone> FusedIterator for Drain<'_, K, A> {}
+
+impl<K: fmt::Debug, A: Allocator + Clone> fmt::Debug for Drain<'_, K, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let entries_iter = self.iter.iter().map(|(k, _)| k);
+        f.debug_list().entries(entries_iter).finish()
+    }
+}
+
+impl<'a, K, F, A: Allocator + Clone> Drop for DrainFilter<'a, K, F, A>
+where
+    F: FnMut(&K) -> bool,
+{
+    #[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);
+        }
+    }
+}
+
+impl<K, F, A: Allocator + Clone> Iterator for DrainFilter<'_, K, F, A>
+where
+    F: FnMut(&K) -> bool,
+{
+    type Item = K;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<Self::Item> {
+        let f = &mut self.f;
+        let (k, _) = self.inner.next(&mut |k, _| f(k))?;
+        Some(k)
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (0, self.inner.iter.size_hint().1)
+    }
+}
+
+impl<K, F, A: Allocator + Clone> FusedIterator for DrainFilter<'_, K, F, A> where
+    F: FnMut(&K) -> bool
+{
+}
+
+impl<T, S, A: Allocator + Clone> Clone for Intersection<'_, T, S, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        Intersection {
+            iter: self.iter.clone(),
+            ..*self
+        }
+    }
+}
+
+impl<'a, T, S, A> Iterator for Intersection<'a, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    type Item = &'a T;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a T> {
+        loop {
+            let elt = self.iter.next()?;
+            if self.other.contains(elt) {
+                return Some(elt);
+            }
+        }
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, upper) = self.iter.size_hint();
+        (0, upper)
+    }
+}
+
+impl<T, S, A> fmt::Debug for Intersection<'_, T, S, A>
+where
+    T: fmt::Debug + Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<T, S, A> FusedIterator for Intersection<'_, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+}
+
+impl<T, S, A: Allocator + Clone> Clone for Difference<'_, T, S, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        Difference {
+            iter: self.iter.clone(),
+            ..*self
+        }
+    }
+}
+
+impl<'a, T, S, A> Iterator for Difference<'a, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    type Item = &'a T;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a T> {
+        loop {
+            let elt = self.iter.next()?;
+            if !self.other.contains(elt) {
+                return Some(elt);
+            }
+        }
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let (_, upper) = self.iter.size_hint();
+        (0, upper)
+    }
+}
+
+impl<T, S, A> FusedIterator for Difference<'_, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+}
+
+impl<T, S, A> fmt::Debug for Difference<'_, T, S, A>
+where
+    T: fmt::Debug + Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<T, S, A: Allocator + Clone> Clone for SymmetricDifference<'_, T, S, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        SymmetricDifference {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<'a, T, S, A> Iterator for SymmetricDifference<'a, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    type Item = &'a T;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a T> {
+        self.iter.next()
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+impl<T, S, A> FusedIterator for SymmetricDifference<'_, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+}
+
+impl<T, S, A> fmt::Debug for SymmetricDifference<'_, T, S, A>
+where
+    T: fmt::Debug + Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<T, S, A: Allocator + Clone> Clone for Union<'_, T, S, A> {
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn clone(&self) -> Self {
+        Union {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<T, S, A> FusedIterator for Union<'_, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+}
+
+impl<T, S, A> fmt::Debug for Union<'_, T, S, A>
+where
+    T: fmt::Debug + Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+impl<'a, T, S, A> Iterator for Union<'a, T, S, A>
+where
+    T: Eq + Hash,
+    S: BuildHasher,
+    A: Allocator + Clone,
+{
+    type Item = &'a T;
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn next(&mut self) -> Option<&'a T> {
+        self.iter.next()
+    }
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}
+
+/// A view into a single entry in a set, which may either be vacant or occupied.
+///
+/// This `enum` is constructed from the [`entry`] method on [`HashSet`].
+///
+/// [`HashSet`]: struct.HashSet.html
+/// [`entry`]: struct.HashSet.html#method.entry
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_set::{Entry, HashSet, OccupiedEntry};
+///
+/// let mut set = HashSet::new();
+/// set.extend(["a", "b", "c"]);
+/// assert_eq!(set.len(), 3);
+///
+/// // Existing value (insert)
+/// let entry: Entry<_, _> = set.entry("a");
+/// let _raw_o: OccupiedEntry<_, _> = entry.insert();
+/// assert_eq!(set.len(), 3);
+/// // Nonexistent value (insert)
+/// set.entry("d").insert();
+///
+/// // Existing value (or_insert)
+/// set.entry("b").or_insert();
+/// // Nonexistent value (or_insert)
+/// set.entry("e").or_insert();
+///
+/// println!("Our HashSet: {:?}", set);
+///
+/// let mut vec: Vec<_> = set.iter().copied().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", "b", "c", "d", "e"]);
+/// ```
+pub enum Entry<'a, T, S, A = Global>
+where
+    A: Allocator + Clone,
+{
+    /// An occupied entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_set::{Entry, HashSet};
+    /// let mut set: HashSet<_> = ["a", "b"].into();
+    ///
+    /// match set.entry("a") {
+    ///     Entry::Vacant(_) => unreachable!(),
+    ///     Entry::Occupied(_) => { }
+    /// }
+    /// ```
+    Occupied(OccupiedEntry<'a, T, S, A>),
+
+    /// A vacant entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_set::{Entry, HashSet};
+    /// let mut set: HashSet<&str> = HashSet::new();
+    ///
+    /// match set.entry("a") {
+    ///     Entry::Occupied(_) => unreachable!(),
+    ///     Entry::Vacant(_) => { }
+    /// }
+    /// ```
+    Vacant(VacantEntry<'a, T, S, A>),
+}
+
+impl<T: fmt::Debug, S, A: Allocator + Clone> fmt::Debug for Entry<'_, T, 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 `HashSet`.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_set::{Entry, HashSet, OccupiedEntry};
+///
+/// let mut set = HashSet::new();
+/// set.extend(["a", "b", "c"]);
+///
+/// let _entry_o: OccupiedEntry<_, _> = set.entry("a").insert();
+/// assert_eq!(set.len(), 3);
+///
+/// // Existing key
+/// match set.entry("a") {
+///     Entry::Vacant(_) => unreachable!(),
+///     Entry::Occupied(view) => {
+///         assert_eq!(view.get(), &"a");
+///     }
+/// }
+///
+/// assert_eq!(set.len(), 3);
+///
+/// // Existing key (take)
+/// match set.entry("c") {
+///     Entry::Vacant(_) => unreachable!(),
+///     Entry::Occupied(view) => {
+///         assert_eq!(view.remove(), "c");
+///     }
+/// }
+/// assert_eq!(set.get(&"c"), None);
+/// assert_eq!(set.len(), 2);
+/// ```
+pub struct OccupiedEntry<'a, T, S, A: Allocator + Clone = Global> {
+    inner: map::OccupiedEntry<'a, T, (), S, A>,
+}
+
+impl<T: fmt::Debug, S, A: Allocator + Clone> fmt::Debug for OccupiedEntry<'_, T, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("OccupiedEntry")
+            .field("value", self.get())
+            .finish()
+    }
+}
+
+/// A view into a vacant entry in a `HashSet`.
+/// It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+///
+/// # Examples
+///
+/// ```
+/// use hashbrown::hash_set::{Entry, HashSet, VacantEntry};
+///
+/// let mut set = HashSet::<&str>::new();
+///
+/// let entry_v: VacantEntry<_, _> = match set.entry("a") {
+///     Entry::Vacant(view) => view,
+///     Entry::Occupied(_) => unreachable!(),
+/// };
+/// entry_v.insert();
+/// assert!(set.contains("a") && set.len() == 1);
+///
+/// // Nonexistent key (insert)
+/// match set.entry("b") {
+///     Entry::Vacant(view) => view.insert(),
+///     Entry::Occupied(_) => unreachable!(),
+/// }
+/// assert!(set.contains("b") && set.len() == 2);
+/// ```
+pub struct VacantEntry<'a, T, S, A: Allocator + Clone = Global> {
+    inner: map::VacantEntry<'a, T, (), S, A>,
+}
+
+impl<T: fmt::Debug, S, A: Allocator + Clone> fmt::Debug for VacantEntry<'_, T, S, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("VacantEntry").field(self.get()).finish()
+    }
+}
+
+impl<'a, T, S, A: Allocator + Clone> Entry<'a, T, S, A> {
+    /// Sets the value of the entry, and returns an OccupiedEntry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    /// let entry = set.entry("horseyland").insert();
+    ///
+    /// assert_eq!(entry.get(), &"horseyland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self) -> OccupiedEntry<'a, T, S, A>
+    where
+        T: Hash,
+        S: BuildHasher,
+    {
+        match self {
+            Entry::Occupied(entry) => entry,
+            Entry::Vacant(entry) => entry.insert_entry(),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting if it was vacant.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    ///
+    /// // nonexistent key
+    /// set.entry("poneyland").or_insert();
+    /// assert!(set.contains("poneyland"));
+    ///
+    /// // existing key
+    /// set.entry("poneyland").or_insert();
+    /// assert!(set.contains("poneyland"));
+    /// assert_eq!(set.len(), 1);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn or_insert(self)
+    where
+        T: Hash,
+        S: BuildHasher,
+    {
+        if let Entry::Vacant(entry) = self {
+            entry.insert();
+        }
+    }
+
+    /// Returns a reference to this entry's value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    /// set.entry("poneyland").or_insert();
+    /// // existing key
+    /// assert_eq!(set.entry("poneyland").get(), &"poneyland");
+    /// // nonexistent key
+    /// assert_eq!(set.entry("horseland").get(), &"horseland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get(&self) -> &T {
+        match *self {
+            Entry::Occupied(ref entry) => entry.get(),
+            Entry::Vacant(ref entry) => entry.get(),
+        }
+    }
+}
+
+impl<T, S, A: Allocator + Clone> OccupiedEntry<'_, T, S, A> {
+    /// Gets a reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_set::{Entry, HashSet};
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    /// set.entry("poneyland").or_insert();
+    ///
+    /// match set.entry("poneyland") {
+    ///     Entry::Vacant(_) => panic!(),
+    ///     Entry::Occupied(entry) => assert_eq!(entry.get(), &"poneyland"),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get(&self) -> &T {
+        self.inner.key()
+    }
+
+    /// Takes the value out of the entry, and returns it.
+    /// Keeps the allocated memory for reuse.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// use hashbrown::hash_set::Entry;
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    /// // The set is empty
+    /// assert!(set.is_empty() && set.capacity() == 0);
+    ///
+    /// set.entry("poneyland").or_insert();
+    /// let capacity_before_remove = set.capacity();
+    ///
+    /// if let Entry::Occupied(o) = set.entry("poneyland") {
+    ///     assert_eq!(o.remove(), "poneyland");
+    /// }
+    ///
+    /// assert_eq!(set.contains("poneyland"), false);
+    /// // Now set hold none elements but capacity is equal to the old one
+    /// assert!(set.len() == 0 && set.capacity() == capacity_before_remove);
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn remove(self) -> T {
+        self.inner.remove_entry().0
+    }
+
+    /// Replaces the entry, returning the old value. The new value in the hash map will be
+    /// the value used to create this entry.
+    ///
+    /// # Panics
+    ///
+    /// Will panic if this OccupiedEntry was created through [`Entry::insert`].
+    ///
+    /// # Examples
+    ///
+    /// ```
+    ///  use hashbrown::hash_set::{Entry, HashSet};
+    ///  use std::rc::Rc;
+    ///
+    ///  let mut set: HashSet<Rc<String>> = HashSet::new();
+    ///  let key_one = Rc::new("Stringthing".to_string());
+    ///  let key_two = Rc::new("Stringthing".to_string());
+    ///
+    ///  set.insert(key_one.clone());
+    ///  assert!(Rc::strong_count(&key_one) == 2 && Rc::strong_count(&key_two) == 1);
+    ///
+    ///  match set.entry(key_two.clone()) {
+    ///      Entry::Occupied(entry) => {
+    ///          let old_key: Rc<String> = entry.replace();
+    ///          assert!(Rc::ptr_eq(&key_one, &old_key));
+    ///      }
+    ///      Entry::Vacant(_) => panic!(),
+    ///  }
+    ///
+    ///  assert!(Rc::strong_count(&key_one) == 1 && Rc::strong_count(&key_two) == 2);
+    ///  assert!(set.contains(&"Stringthing".to_owned()));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn replace(self) -> T {
+        self.inner.replace_key()
+    }
+}
+
+impl<'a, T, S, A: Allocator + Clone> VacantEntry<'a, T, S, A> {
+    /// Gets a reference to the value that would be used when inserting
+    /// through the `VacantEntry`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    /// assert_eq!(set.entry("poneyland").get(), &"poneyland");
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn get(&self) -> &T {
+        self.inner.key()
+    }
+
+    /// Take ownership of the value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::hash_set::{Entry, HashSet};
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    ///
+    /// match set.entry("poneyland") {
+    ///     Entry::Occupied(_) => panic!(),
+    ///     Entry::Vacant(v) => assert_eq!(v.into_value(), "poneyland"),
+    /// }
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn into_value(self) -> T {
+        self.inner.into_key()
+    }
+
+    /// Sets the value of the entry with the VacantEntry's value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use hashbrown::HashSet;
+    /// use hashbrown::hash_set::Entry;
+    ///
+    /// let mut set: HashSet<&str> = HashSet::new();
+    ///
+    /// if let Entry::Vacant(o) = set.entry("poneyland") {
+    ///     o.insert();
+    /// }
+    /// assert!(set.contains("poneyland"));
+    /// ```
+    #[cfg_attr(feature = "inline-more", inline)]
+    pub fn insert(self)
+    where
+        T: Hash,
+        S: BuildHasher,
+    {
+        self.inner.insert(());
+    }
+
+    #[cfg_attr(feature = "inline-more", inline)]
+    fn insert_entry(self) -> OccupiedEntry<'a, T, S, A>
+    where
+        T: Hash,
+        S: BuildHasher,
+    {
+        OccupiedEntry {
+            inner: self.inner.insert_entry(()),
+        }
+    }
+}
+
+#[allow(dead_code)]
+fn assert_covariance() {
+    fn set<'new>(v: HashSet<&'static str>) -> HashSet<&'new str> {
+        v
+    }
+    fn iter<'a, 'new>(v: Iter<'a, &'static str>) -> Iter<'a, &'new str> {
+        v
+    }
+    fn into_iter<'new, A: Allocator + Clone>(
+        v: IntoIter<&'static str, A>,
+    ) -> IntoIter<&'new str, A> {
+        v
+    }
+    fn difference<'a, 'new, A: Allocator + Clone>(
+        v: Difference<'a, &'static str, DefaultHashBuilder, A>,
+    ) -> Difference<'a, &'new str, DefaultHashBuilder, A> {
+        v
+    }
+    fn symmetric_difference<'a, 'new, A: Allocator + Clone>(
+        v: SymmetricDifference<'a, &'static str, DefaultHashBuilder, A>,
+    ) -> SymmetricDifference<'a, &'new str, DefaultHashBuilder, A> {
+        v
+    }
+    fn intersection<'a, 'new, A: Allocator + Clone>(
+        v: Intersection<'a, &'static str, DefaultHashBuilder, A>,
+    ) -> Intersection<'a, &'new str, DefaultHashBuilder, A> {
+        v
+    }
+    fn union<'a, 'new, A: Allocator + Clone>(
+        v: Union<'a, &'static str, DefaultHashBuilder, A>,
+    ) -> Union<'a, &'new str, DefaultHashBuilder, A> {
+        v
+    }
+    fn drain<'new, A: Allocator + Clone>(
+        d: Drain<'static, &'static str, A>,
+    ) -> Drain<'new, &'new str, A> {
+        d
+    }
+}
+
+#[cfg(test)]
+mod test_set {
+    use super::super::map::DefaultHashBuilder;
+    use super::HashSet;
+    use std::vec::Vec;
+
+    #[test]
+    fn test_zero_capacities() {
+        type HS = HashSet<i32>;
+
+        let s = HS::new();
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::default();
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::with_hasher(DefaultHashBuilder::default());
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::with_capacity(0);
+        assert_eq!(s.capacity(), 0);
+
+        let s = HS::with_capacity_and_hasher(0, DefaultHashBuilder::default());
+        assert_eq!(s.capacity(), 0);
+
+        let mut s = HS::new();
+        s.insert(1);
+        s.insert(2);
+        s.remove(&1);
+        s.remove(&2);
+        s.shrink_to_fit();
+        assert_eq!(s.capacity(), 0);
+
+        let mut s = HS::new();
+        s.reserve(0);
+        assert_eq!(s.capacity(), 0);
+    }
+
+    #[test]
+    fn test_disjoint() {
+        let mut xs = HashSet::new();
+        let mut ys = HashSet::new();
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(xs.insert(5));
+        assert!(ys.insert(11));
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(xs.insert(7));
+        assert!(xs.insert(19));
+        assert!(xs.insert(4));
+        assert!(ys.insert(2));
+        assert!(ys.insert(-11));
+        assert!(xs.is_disjoint(&ys));
+        assert!(ys.is_disjoint(&xs));
+        assert!(ys.insert(7));
+        assert!(!xs.is_disjoint(&ys));
+        assert!(!ys.is_disjoint(&xs));
+    }
+
+    #[test]
+    fn test_subset_and_superset() {
+        let mut a = HashSet::new();
+        assert!(a.insert(0));
+        assert!(a.insert(5));
+        assert!(a.insert(11));
+        assert!(a.insert(7));
+
+        let mut b = HashSet::new();
+        assert!(b.insert(0));
+        assert!(b.insert(7));
+        assert!(b.insert(19));
+        assert!(b.insert(250));
+        assert!(b.insert(11));
+        assert!(b.insert(200));
+
+        assert!(!a.is_subset(&b));
+        assert!(!a.is_superset(&b));
+        assert!(!b.is_subset(&a));
+        assert!(!b.is_superset(&a));
+
+        assert!(b.insert(5));
+
+        assert!(a.is_subset(&b));
+        assert!(!a.is_superset(&b));
+        assert!(!b.is_subset(&a));
+        assert!(b.is_superset(&a));
+    }
+
+    #[test]
+    fn test_iterate() {
+        let mut a = HashSet::new();
+        for i in 0..32 {
+            assert!(a.insert(i));
+        }
+        let mut observed: u32 = 0;
+        for k in &a {
+            observed |= 1 << *k;
+        }
+        assert_eq!(observed, 0xFFFF_FFFF);
+    }
+
+    #[test]
+    fn test_intersection() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(11));
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(77));
+        assert!(a.insert(103));
+        assert!(a.insert(5));
+        assert!(a.insert(-5));
+
+        assert!(b.insert(2));
+        assert!(b.insert(11));
+        assert!(b.insert(77));
+        assert!(b.insert(-9));
+        assert!(b.insert(-42));
+        assert!(b.insert(5));
+        assert!(b.insert(3));
+
+        let mut i = 0;
+        let expected = [3, 5, 11, 77];
+        for x in a.intersection(&b) {
+            assert!(expected.contains(x));
+            i += 1;
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_difference() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+
+        assert!(b.insert(3));
+        assert!(b.insert(9));
+
+        let mut i = 0;
+        let expected = [1, 5, 11];
+        for x in a.difference(&b) {
+            assert!(expected.contains(x));
+            i += 1;
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_symmetric_difference() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+
+        assert!(b.insert(-2));
+        assert!(b.insert(3));
+        assert!(b.insert(9));
+        assert!(b.insert(14));
+        assert!(b.insert(22));
+
+        let mut i = 0;
+        let expected = [-2, 1, 5, 11, 14, 22];
+        for x in a.symmetric_difference(&b) {
+            assert!(expected.contains(x));
+            i += 1;
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_union() {
+        let mut a = HashSet::new();
+        let mut b = HashSet::new();
+
+        assert!(a.insert(1));
+        assert!(a.insert(3));
+        assert!(a.insert(5));
+        assert!(a.insert(9));
+        assert!(a.insert(11));
+        assert!(a.insert(16));
+        assert!(a.insert(19));
+        assert!(a.insert(24));
+
+        assert!(b.insert(-2));
+        assert!(b.insert(1));
+        assert!(b.insert(5));
+        assert!(b.insert(9));
+        assert!(b.insert(13));
+        assert!(b.insert(19));
+
+        let mut i = 0;
+        let expected = [-2, 1, 3, 5, 9, 11, 13, 16, 19, 24];
+        for x in a.union(&b) {
+            assert!(expected.contains(x));
+            i += 1;
+        }
+        assert_eq!(i, expected.len());
+    }
+
+    #[test]
+    fn test_from_map() {
+        let mut a = crate::HashMap::new();
+        a.insert(1, ());
+        a.insert(2, ());
+        a.insert(3, ());
+        a.insert(4, ());
+
+        let a: HashSet<_> = a.into();
+
+        assert_eq!(a.len(), 4);
+        assert!(a.contains(&1));
+        assert!(a.contains(&2));
+        assert!(a.contains(&3));
+        assert!(a.contains(&4));
+    }
+
+    #[test]
+    fn test_from_iter() {
+        let xs = [1, 2, 2, 3, 4, 5, 6, 7, 8, 9];
+
+        let set: HashSet<_> = xs.iter().copied().collect();
+
+        for x in &xs {
+            assert!(set.contains(x));
+        }
+
+        assert_eq!(set.iter().len(), xs.len() - 1);
+    }
+
+    #[test]
+    fn test_move_iter() {
+        let hs = {
+            let mut hs = HashSet::new();
+
+            hs.insert('a');
+            hs.insert('b');
+
+            hs
+        };
+
+        let v = hs.into_iter().collect::<Vec<char>>();
+        assert!(v == ['a', 'b'] || v == ['b', 'a']);
+    }
+
+    #[test]
+    fn test_eq() {
+        // These constants once happened to expose a bug in insert().
+        // I'm keeping them around to prevent a regression.
+        let mut s1 = HashSet::new();
+
+        s1.insert(1);
+        s1.insert(2);
+        s1.insert(3);
+
+        let mut s2 = HashSet::new();
+
+        s2.insert(1);
+        s2.insert(2);
+
+        assert!(s1 != s2);
+
+        s2.insert(3);
+
+        assert_eq!(s1, s2);
+    }
+
+    #[test]
+    fn test_show() {
+        let mut set = HashSet::new();
+        let empty = HashSet::<i32>::new();
+
+        set.insert(1);
+        set.insert(2);
+
+        let set_str = format!("{:?}", set);
+
+        assert!(set_str == "{1, 2}" || set_str == "{2, 1}");
+        assert_eq!(format!("{:?}", empty), "{}");
+    }
+
+    #[test]
+    fn test_trivial_drain() {
+        let mut s = HashSet::<i32>::new();
+        for _ in s.drain() {}
+        assert!(s.is_empty());
+        drop(s);
+
+        let mut s = HashSet::<i32>::new();
+        drop(s.drain());
+        assert!(s.is_empty());
+    }
+
+    #[test]
+    fn test_drain() {
+        let mut s: HashSet<_> = (1..100).collect();
+
+        // try this a bunch of times to make sure we don't screw up internal state.
+        for _ in 0..20 {
+            assert_eq!(s.len(), 99);
+
+            {
+                let mut last_i = 0;
+                let mut d = s.drain();
+                for (i, x) in d.by_ref().take(50).enumerate() {
+                    last_i = i;
+                    assert!(x != 0);
+                }
+                assert_eq!(last_i, 49);
+            }
+
+            for _ in &s {
+                panic!("s should be empty!");
+            }
+
+            // reset to try again.
+            s.extend(1..100);
+        }
+    }
+
+    #[test]
+    fn test_replace() {
+        use core::hash;
+
+        #[derive(Debug)]
+        struct Foo(&'static str, i32);
+
+        impl PartialEq for Foo {
+            fn eq(&self, other: &Self) -> bool {
+                self.0 == other.0
+            }
+        }
+
+        impl Eq for Foo {}
+
+        impl hash::Hash for Foo {
+            fn hash<H: hash::Hasher>(&self, h: &mut H) {
+                self.0.hash(h);
+            }
+        }
+
+        let mut s = HashSet::new();
+        assert_eq!(s.replace(Foo("a", 1)), None);
+        assert_eq!(s.len(), 1);
+        assert_eq!(s.replace(Foo("a", 2)), Some(Foo("a", 1)));
+        assert_eq!(s.len(), 1);
+
+        let mut it = s.iter();
+        assert_eq!(it.next(), Some(&Foo("a", 2)));
+        assert_eq!(it.next(), None);
+    }
+
+    #[test]
+    fn test_extend_ref() {
+        let mut a = HashSet::new();
+        a.insert(1);
+
+        a.extend(&[2, 3, 4]);
+
+        assert_eq!(a.len(), 4);
+        assert!(a.contains(&1));
+        assert!(a.contains(&2));
+        assert!(a.contains(&3));
+        assert!(a.contains(&4));
+
+        let mut b = HashSet::new();
+        b.insert(5);
+        b.insert(6);
+
+        a.extend(&b);
+
+        assert_eq!(a.len(), 6);
+        assert!(a.contains(&1));
+        assert!(a.contains(&2));
+        assert!(a.contains(&3));
+        assert!(a.contains(&4));
+        assert!(a.contains(&5));
+        assert!(a.contains(&6));
+    }
+
+    #[test]
+    fn test_retain() {
+        let xs = [1, 2, 3, 4, 5, 6];
+        let mut set: HashSet<i32> = xs.iter().copied().collect();
+        set.retain(|&k| k % 2 == 0);
+        assert_eq!(set.len(), 3);
+        assert!(set.contains(&2));
+        assert!(set.contains(&4));
+        assert!(set.contains(&6));
+    }
+
+    #[test]
+    fn test_drain_filter() {
+        {
+            let mut set: HashSet<i32> = (0..8).collect();
+            let drained = set.drain_filter(|&k| k % 2 == 0);
+            let mut out = drained.collect::<Vec<_>>();
+            out.sort_unstable();
+            assert_eq!(vec![0, 2, 4, 6], out);
+            assert_eq!(set.len(), 4);
+        }
+        {
+            let mut set: HashSet<i32> = (0..8).collect();
+            drop(set.drain_filter(|&k| k % 2 == 0));
+            assert_eq!(set.len(), 4, "Removes non-matching items on drop");
+        }
+    }
+
+    #[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_SET: HashSet<u32, MyHasher> = HashSet::with_hasher(MyHasher);
+
+        let mut set = EMPTY_SET;
+        set.insert(19);
+        assert!(set.contains(&19));
+    }
+
+    #[test]
+    fn rehash_in_place() {
+        let mut set = HashSet::new();
+
+        for i in 0..224 {
+            set.insert(i);
+        }
+
+        assert_eq!(
+            set.capacity(),
+            224,
+            "The set must be at or close to capacity to trigger a re hashing"
+        );
+
+        for i in 100..1400 {
+            set.remove(&(i - 100));
+            set.insert(i);
+        }
+    }
+}