Adding upstream version 0.70.1+ds1.upstream/0.70.1+ds1upstream

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

1 files changed, 1947 insertions, 0 deletions

diff --git a/vendor/indexmap-1.9.3/src/map.rs b/vendor/indexmap-1.9.3/src/map.rs
new file mode 100644
index 0000000..d39448d
--- /dev/null
+++ b/vendor/indexmap-1.9.3/src/map.rs
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+//! `IndexMap` is a hash table where the iteration order of the key-value
+//! pairs is independent of the hash values of the keys.
+
+mod core;
+
+pub use crate::mutable_keys::MutableKeys;
+
+#[cfg(feature = "rayon")]
+pub use crate::rayon::map as rayon;
+
+use crate::vec::{self, Vec};
+use ::core::cmp::Ordering;
+use ::core::fmt;
+use ::core::hash::{BuildHasher, Hash, Hasher};
+use ::core::iter::FusedIterator;
+use ::core::ops::{Index, IndexMut, RangeBounds};
+use ::core::slice::{Iter as SliceIter, IterMut as SliceIterMut};
+
+#[cfg(has_std)]
+use std::collections::hash_map::RandomState;
+
+use self::core::IndexMapCore;
+use crate::equivalent::Equivalent;
+use crate::util::third;
+use crate::{Bucket, Entries, HashValue};
+
+pub use self::core::{Entry, OccupiedEntry, VacantEntry};
+
+/// A hash table where the iteration order of the key-value pairs is independent
+/// of the hash values of the keys.
+///
+/// The interface is closely compatible with the standard `HashMap`, but also
+/// has additional features.
+///
+/// # Order
+///
+/// The key-value pairs have a consistent order that is determined by
+/// the sequence of insertion and removal calls on the map. The order does
+/// not depend on the keys or the hash function at all.
+///
+/// All iterators traverse the map in *the order*.
+///
+/// The insertion order is preserved, with **notable exceptions** like the
+/// `.remove()` or `.swap_remove()` methods. Methods such as `.sort_by()` of
+/// course result in a new order, depending on the sorting order.
+///
+/// # Indices
+///
+/// The key-value pairs are indexed in a compact range without holes in the
+/// range `0..self.len()`. For example, the method `.get_full` looks up the
+/// index for a key, and the method `.get_index` looks up the key-value pair by
+/// index.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// // count the frequency of each letter in a sentence.
+/// let mut letters = IndexMap::new();
+/// for ch in "a short treatise on fungi".chars() {
+///     *letters.entry(ch).or_insert(0) += 1;
+/// }
+///
+/// assert_eq!(letters[&'s'], 2);
+/// assert_eq!(letters[&'t'], 3);
+/// assert_eq!(letters[&'u'], 1);
+/// assert_eq!(letters.get(&'y'), None);
+/// ```
+#[cfg(has_std)]
+pub struct IndexMap<K, V, S = RandomState> {
+    pub(crate) core: IndexMapCore<K, V>,
+    hash_builder: S,
+}
+#[cfg(not(has_std))]
+pub struct IndexMap<K, V, S> {
+    pub(crate) core: IndexMapCore<K, V>,
+    hash_builder: S,
+}
+
+impl<K, V, S> Clone for IndexMap<K, V, S>
+where
+    K: Clone,
+    V: Clone,
+    S: Clone,
+{
+    fn clone(&self) -> Self {
+        IndexMap {
+            core: self.core.clone(),
+            hash_builder: self.hash_builder.clone(),
+        }
+    }
+
+    fn clone_from(&mut self, other: &Self) {
+        self.core.clone_from(&other.core);
+        self.hash_builder.clone_from(&other.hash_builder);
+    }
+}
+
+impl<K, V, S> Entries for IndexMap<K, V, S> {
+    type Entry = Bucket<K, V>;
+
+    #[inline]
+    fn into_entries(self) -> Vec<Self::Entry> {
+        self.core.into_entries()
+    }
+
+    #[inline]
+    fn as_entries(&self) -> &[Self::Entry] {
+        self.core.as_entries()
+    }
+
+    #[inline]
+    fn as_entries_mut(&mut self) -> &mut [Self::Entry] {
+        self.core.as_entries_mut()
+    }
+
+    fn with_entries<F>(&mut self, f: F)
+    where
+        F: FnOnce(&mut [Self::Entry]),
+    {
+        self.core.with_entries(f);
+    }
+}
+
+impl<K, V, S> fmt::Debug for IndexMap<K, V, S>
+where
+    K: fmt::Debug,
+    V: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        if cfg!(not(feature = "test_debug")) {
+            f.debug_map().entries(self.iter()).finish()
+        } else {
+            // Let the inner `IndexMapCore` print all of its details
+            f.debug_struct("IndexMap")
+                .field("core", &self.core)
+                .finish()
+        }
+    }
+}
+
+#[cfg(has_std)]
+impl<K, V> IndexMap<K, V> {
+    /// Create a new map. (Does not allocate.)
+    #[inline]
+    pub fn new() -> Self {
+        Self::with_capacity(0)
+    }
+
+    /// Create a new map with capacity for `n` key-value pairs. (Does not
+    /// allocate if `n` is zero.)
+    ///
+    /// Computes in **O(n)** time.
+    #[inline]
+    pub fn with_capacity(n: usize) -> Self {
+        Self::with_capacity_and_hasher(n, <_>::default())
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S> {
+    /// Create a new map with capacity for `n` key-value pairs. (Does not
+    /// allocate if `n` is zero.)
+    ///
+    /// Computes in **O(n)** time.
+    #[inline]
+    pub fn with_capacity_and_hasher(n: usize, hash_builder: S) -> Self {
+        if n == 0 {
+            Self::with_hasher(hash_builder)
+        } else {
+            IndexMap {
+                core: IndexMapCore::with_capacity(n),
+                hash_builder,
+            }
+        }
+    }
+
+    /// Create a new map with `hash_builder`.
+    ///
+    /// This function is `const`, so it
+    /// can be called in `static` contexts.
+    pub const fn with_hasher(hash_builder: S) -> Self {
+        IndexMap {
+            core: IndexMapCore::new(),
+            hash_builder,
+        }
+    }
+
+    /// Computes in **O(1)** time.
+    pub fn capacity(&self) -> usize {
+        self.core.capacity()
+    }
+
+    /// Return a reference to the map's `BuildHasher`.
+    pub fn hasher(&self) -> &S {
+        &self.hash_builder
+    }
+
+    /// Return the number of key-value pairs in the map.
+    ///
+    /// Computes in **O(1)** time.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.core.len()
+    }
+
+    /// Returns true if the map contains no elements.
+    ///
+    /// Computes in **O(1)** time.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Return an iterator over the key-value pairs of the map, in their order
+    pub fn iter(&self) -> Iter<'_, K, V> {
+        Iter {
+            iter: self.as_entries().iter(),
+        }
+    }
+
+    /// Return an iterator over the key-value pairs of the map, in their order
+    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
+        IterMut {
+            iter: self.as_entries_mut().iter_mut(),
+        }
+    }
+
+    /// Return an iterator over the keys of the map, in their order
+    pub fn keys(&self) -> Keys<'_, K, V> {
+        Keys {
+            iter: self.as_entries().iter(),
+        }
+    }
+
+    /// Return an owning iterator over the keys of the map, in their order
+    pub fn into_keys(self) -> IntoKeys<K, V> {
+        IntoKeys {
+            iter: self.into_entries().into_iter(),
+        }
+    }
+
+    /// Return an iterator over the values of the map, in their order
+    pub fn values(&self) -> Values<'_, K, V> {
+        Values {
+            iter: self.as_entries().iter(),
+        }
+    }
+
+    /// Return an iterator over mutable references to the values of the map,
+    /// in their order
+    pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
+        ValuesMut {
+            iter: self.as_entries_mut().iter_mut(),
+        }
+    }
+
+    /// Return an owning iterator over the values of the map, in their order
+    pub fn into_values(self) -> IntoValues<K, V> {
+        IntoValues {
+            iter: self.into_entries().into_iter(),
+        }
+    }
+
+    /// Remove all key-value pairs in the map, while preserving its capacity.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn clear(&mut self) {
+        self.core.clear();
+    }
+
+    /// Shortens the map, keeping the first `len` elements and dropping the rest.
+    ///
+    /// If `len` is greater than the map's current length, this has no effect.
+    pub fn truncate(&mut self, len: usize) {
+        self.core.truncate(len);
+    }
+
+    /// Clears the `IndexMap` in the given index range, returning those
+    /// key-value pairs as a drain iterator.
+    ///
+    /// The range may be any type that implements `RangeBounds<usize>`,
+    /// including all of the `std::ops::Range*` types, or even a tuple pair of
+    /// `Bound` start and end values. To drain the map entirely, use `RangeFull`
+    /// like `map.drain(..)`.
+    ///
+    /// This shifts down all entries following the drained range to fill the
+    /// gap, and keeps the allocated memory for reuse.
+    ///
+    /// ***Panics*** if the starting point is greater than the end point or if
+    /// the end point is greater than the length of the map.
+    pub fn drain<R>(&mut self, range: R) -> Drain<'_, K, V>
+    where
+        R: RangeBounds<usize>,
+    {
+        Drain {
+            iter: self.core.drain(range),
+        }
+    }
+
+    /// Splits the collection into two at the given index.
+    ///
+    /// Returns a newly allocated map containing the elements in the range
+    /// `[at, len)`. After the call, the original map will be left containing
+    /// the elements `[0, at)` with its previous capacity unchanged.
+    ///
+    /// ***Panics*** if `at > len`.
+    pub fn split_off(&mut self, at: usize) -> Self
+    where
+        S: Clone,
+    {
+        Self {
+            core: self.core.split_off(at),
+            hash_builder: self.hash_builder.clone(),
+        }
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S>
+where
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    /// Reserve capacity for `additional` more key-value pairs.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn reserve(&mut self, additional: usize) {
+        self.core.reserve(additional);
+    }
+
+    /// Shrink the capacity of the map as much as possible.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn shrink_to_fit(&mut self) {
+        self.core.shrink_to(0);
+    }
+
+    /// Shrink the capacity of the map with a lower limit.
+    ///
+    /// Computes in **O(n)** time.
+    pub fn shrink_to(&mut self, min_capacity: usize) {
+        self.core.shrink_to(min_capacity);
+    }
+
+    fn hash<Q: ?Sized + Hash>(&self, key: &Q) -> HashValue {
+        let mut h = self.hash_builder.build_hasher();
+        key.hash(&mut h);
+        HashValue(h.finish() as usize)
+    }
+
+    /// Insert a key-value pair in the map.
+    ///
+    /// If an equivalent key already exists in the map: the key remains and
+    /// retains in its place in the order, its corresponding value is updated
+    /// with `value` and the older value is returned inside `Some(_)`.
+    ///
+    /// If no equivalent key existed in the map: the new key-value pair is
+    /// inserted, last in order, and `None` is returned.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    ///
+    /// See also [`entry`](#method.entry) if you you want to insert *or* modify
+    /// or if you need to get the index of the corresponding key-value pair.
+    pub fn insert(&mut self, key: K, value: V) -> Option<V> {
+        self.insert_full(key, value).1
+    }
+
+    /// Insert a key-value pair in the map, and get their index.
+    ///
+    /// If an equivalent key already exists in the map: the key remains and
+    /// retains in its place in the order, its corresponding value is updated
+    /// with `value` and the older value is returned inside `(index, Some(_))`.
+    ///
+    /// If no equivalent key existed in the map: the new key-value pair is
+    /// inserted, last in order, and `(index, None)` is returned.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    ///
+    /// See also [`entry`](#method.entry) if you you want to insert *or* modify
+    /// or if you need to get the index of the corresponding key-value pair.
+    pub fn insert_full(&mut self, key: K, value: V) -> (usize, Option<V>) {
+        let hash = self.hash(&key);
+        self.core.insert_full(hash, key, value)
+    }
+
+    /// Get the given key’s corresponding entry in the map for insertion and/or
+    /// in-place manipulation.
+    ///
+    /// Computes in **O(1)** time (amortized average).
+    pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
+        let hash = self.hash(&key);
+        self.core.entry(hash, key)
+    }
+
+    /// Return `true` if an equivalent to `key` exists in the map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.get_index_of(key).is_some()
+    }
+
+    /// Return a reference to the value stored for `key`, if it is present,
+    /// else `None`.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn get<Q: ?Sized>(&self, key: &Q) -> Option<&V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &self.as_entries()[i];
+            Some(&entry.value)
+        } else {
+            None
+        }
+    }
+
+    /// Return references to the key-value pair stored for `key`,
+    /// if it is present, else `None`.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn get_key_value<Q: ?Sized>(&self, key: &Q) -> Option<(&K, &V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &self.as_entries()[i];
+            Some((&entry.key, &entry.value))
+        } else {
+            None
+        }
+    }
+
+    /// Return item index, key and value
+    pub fn get_full<Q: ?Sized>(&self, key: &Q) -> Option<(usize, &K, &V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &self.as_entries()[i];
+            Some((i, &entry.key, &entry.value))
+        } else {
+            None
+        }
+    }
+
+    /// Return item index, if it exists in the map
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn get_index_of<Q: ?Sized>(&self, key: &Q) -> Option<usize>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if self.is_empty() {
+            None
+        } else {
+            let hash = self.hash(key);
+            self.core.get_index_of(hash, key)
+        }
+    }
+
+    pub fn get_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<&mut V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &mut self.as_entries_mut()[i];
+            Some(&mut entry.value)
+        } else {
+            None
+        }
+    }
+
+    pub fn get_full_mut<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, &K, &mut V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &mut self.as_entries_mut()[i];
+            Some((i, &entry.key, &mut entry.value))
+        } else {
+            None
+        }
+    }
+
+    pub(crate) fn get_full_mut2_impl<Q: ?Sized>(
+        &mut self,
+        key: &Q,
+    ) -> Option<(usize, &mut K, &mut V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if let Some(i) = self.get_index_of(key) {
+            let entry = &mut self.as_entries_mut()[i];
+            Some((i, &mut entry.key, &mut entry.value))
+        } else {
+            None
+        }
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return
+    /// its value.
+    ///
+    /// **NOTE:** This is equivalent to `.swap_remove(key)`, if you need to
+    /// preserve the order of the keys in the map, use `.shift_remove(key)`
+    /// instead.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.swap_remove(key)
+    }
+
+    /// Remove and return the key-value pair equivalent to `key`.
+    ///
+    /// **NOTE:** This is equivalent to `.swap_remove_entry(key)`, if you need to
+    /// preserve the order of the keys in the map, use `.shift_remove_entry(key)`
+    /// instead.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.swap_remove_entry(key)
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return
+    /// its value.
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the position of what used to be the last element!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.swap_remove_full(key).map(third)
+    }
+
+    /// Remove and return the key-value pair equivalent to `key`.
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the position of what used to be the last element!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        match self.swap_remove_full(key) {
+            Some((_, key, value)) => Some((key, value)),
+            None => None,
+        }
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return it and
+    /// the index it had.
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the position of what used to be the last element!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if self.is_empty() {
+            return None;
+        }
+        let hash = self.hash(key);
+        self.core.swap_remove_full(hash, key)
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return
+    /// its value.
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove<Q: ?Sized>(&mut self, key: &Q) -> Option<V>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        self.shift_remove_full(key).map(third)
+    }
+
+    /// Remove and return the key-value pair equivalent to `key`.
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_entry<Q: ?Sized>(&mut self, key: &Q) -> Option<(K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        match self.shift_remove_full(key) {
+            Some((_, key, value)) => Some((key, value)),
+            None => None,
+        }
+    }
+
+    /// Remove the key-value pair equivalent to `key` and return it and
+    /// the index it had.
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Return `None` if `key` is not in map.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_full<Q: ?Sized>(&mut self, key: &Q) -> Option<(usize, K, V)>
+    where
+        Q: Hash + Equivalent<K>,
+    {
+        if self.is_empty() {
+            return None;
+        }
+        let hash = self.hash(key);
+        self.core.shift_remove_full(hash, key)
+    }
+
+    /// Remove the last key-value pair
+    ///
+    /// This preserves the order of the remaining elements.
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn pop(&mut self) -> Option<(K, V)> {
+        self.core.pop()
+    }
+
+    /// Scan through each key-value pair in the map and keep those where the
+    /// closure `keep` returns `true`.
+    ///
+    /// The elements are visited in order, and remaining elements keep their
+    /// order.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn retain<F>(&mut self, mut keep: F)
+    where
+        F: FnMut(&K, &mut V) -> bool,
+    {
+        self.core.retain_in_order(move |k, v| keep(k, v));
+    }
+
+    pub(crate) fn retain_mut<F>(&mut self, keep: F)
+    where
+        F: FnMut(&mut K, &mut V) -> bool,
+    {
+        self.core.retain_in_order(keep);
+    }
+
+    /// Sort the map’s key-value pairs by the default ordering of the keys.
+    ///
+    /// See [`sort_by`](Self::sort_by) for details.
+    pub fn sort_keys(&mut self)
+    where
+        K: Ord,
+    {
+        self.with_entries(move |entries| {
+            entries.sort_by(move |a, b| K::cmp(&a.key, &b.key));
+        });
+    }
+
+    /// Sort the map’s key-value pairs in place using the comparison
+    /// function `cmp`.
+    ///
+    /// The comparison function receives two key and value pairs to compare (you
+    /// can sort by keys or values or their combination as needed).
+    ///
+    /// Computes in **O(n log n + c)** time and **O(n)** space where *n* is
+    /// the length of the map and *c* the capacity. The sort is stable.
+    pub fn sort_by<F>(&mut self, mut cmp: F)
+    where
+        F: FnMut(&K, &V, &K, &V) -> Ordering,
+    {
+        self.with_entries(move |entries| {
+            entries.sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        });
+    }
+
+    /// Sort the key-value pairs of the map and return a by-value iterator of
+    /// the key-value pairs with the result.
+    ///
+    /// The sort is stable.
+    pub fn sorted_by<F>(self, mut cmp: F) -> IntoIter<K, V>
+    where
+        F: FnMut(&K, &V, &K, &V) -> Ordering,
+    {
+        let mut entries = self.into_entries();
+        entries.sort_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        IntoIter {
+            iter: entries.into_iter(),
+        }
+    }
+
+    /// Sort the map's key-value pairs by the default ordering of the keys, but
+    /// may not preserve the order of equal elements.
+    ///
+    /// See [`sort_unstable_by`](Self::sort_unstable_by) for details.
+    pub fn sort_unstable_keys(&mut self)
+    where
+        K: Ord,
+    {
+        self.with_entries(move |entries| {
+            entries.sort_unstable_by(move |a, b| K::cmp(&a.key, &b.key));
+        });
+    }
+
+    /// Sort the map's key-value pairs in place using the comparison function `cmp`, but
+    /// may not preserve the order of equal elements.
+    ///
+    /// The comparison function receives two key and value pairs to compare (you
+    /// can sort by keys or values or their combination as needed).
+    ///
+    /// Computes in **O(n log n + c)** time where *n* is
+    /// the length of the map and *c* is the capacity. The sort is unstable.
+    pub fn sort_unstable_by<F>(&mut self, mut cmp: F)
+    where
+        F: FnMut(&K, &V, &K, &V) -> Ordering,
+    {
+        self.with_entries(move |entries| {
+            entries.sort_unstable_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        });
+    }
+
+    /// Sort the key-value pairs of the map and return a by-value iterator of
+    /// the key-value pairs with the result.
+    ///
+    /// The sort is unstable.
+    #[inline]
+    pub fn sorted_unstable_by<F>(self, mut cmp: F) -> IntoIter<K, V>
+    where
+        F: FnMut(&K, &V, &K, &V) -> Ordering,
+    {
+        let mut entries = self.into_entries();
+        entries.sort_unstable_by(move |a, b| cmp(&a.key, &a.value, &b.key, &b.value));
+        IntoIter {
+            iter: entries.into_iter(),
+        }
+    }
+
+    /// Reverses the order of the map’s key-value pairs in place.
+    ///
+    /// Computes in **O(n)** time and **O(1)** space.
+    pub fn reverse(&mut self) {
+        self.core.reverse()
+    }
+}
+
+impl<K, V, S> IndexMap<K, V, S> {
+    /// Get a key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Computes in **O(1)** time.
+    pub fn get_index(&self, index: usize) -> Option<(&K, &V)> {
+        self.as_entries().get(index).map(Bucket::refs)
+    }
+
+    /// Get a key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Computes in **O(1)** time.
+    pub fn get_index_mut(&mut self, index: usize) -> Option<(&mut K, &mut V)> {
+        self.as_entries_mut().get_mut(index).map(Bucket::muts)
+    }
+
+    /// Get the first key-value pair
+    ///
+    /// Computes in **O(1)** time.
+    pub fn first(&self) -> Option<(&K, &V)> {
+        self.as_entries().first().map(Bucket::refs)
+    }
+
+    /// Get the first key-value pair, with mutable access to the value
+    ///
+    /// Computes in **O(1)** time.
+    pub fn first_mut(&mut self) -> Option<(&K, &mut V)> {
+        self.as_entries_mut().first_mut().map(Bucket::ref_mut)
+    }
+
+    /// Get the last key-value pair
+    ///
+    /// Computes in **O(1)** time.
+    pub fn last(&self) -> Option<(&K, &V)> {
+        self.as_entries().last().map(Bucket::refs)
+    }
+
+    /// Get the last key-value pair, with mutable access to the value
+    ///
+    /// Computes in **O(1)** time.
+    pub fn last_mut(&mut self) -> Option<(&K, &mut V)> {
+        self.as_entries_mut().last_mut().map(Bucket::ref_mut)
+    }
+
+    /// Remove the key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Like `Vec::swap_remove`, the pair is removed by swapping it with the
+    /// last element of the map and popping it off. **This perturbs
+    /// the position of what used to be the last element!**
+    ///
+    /// Computes in **O(1)** time (average).
+    pub fn swap_remove_index(&mut self, index: usize) -> Option<(K, V)> {
+        self.core.swap_remove_index(index)
+    }
+
+    /// Remove the key-value pair by index
+    ///
+    /// Valid indices are *0 <= index < self.len()*
+    ///
+    /// Like `Vec::remove`, the pair is removed by shifting all of the
+    /// elements that follow it, preserving their relative order.
+    /// **This perturbs the index of all of those elements!**
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn shift_remove_index(&mut self, index: usize) -> Option<(K, V)> {
+        self.core.shift_remove_index(index)
+    }
+
+    /// Moves the position of a key-value pair from one index to another
+    /// by shifting all other pairs in-between.
+    ///
+    /// * If `from < to`, the other pairs will shift down while the targeted pair moves up.
+    /// * If `from > to`, the other pairs will shift up while the targeted pair moves down.
+    ///
+    /// ***Panics*** if `from` or `to` are out of bounds.
+    ///
+    /// Computes in **O(n)** time (average).
+    pub fn move_index(&mut self, from: usize, to: usize) {
+        self.core.move_index(from, to)
+    }
+
+    /// Swaps the position of two key-value pairs in the map.
+    ///
+    /// ***Panics*** if `a` or `b` are out of bounds.
+    pub fn swap_indices(&mut self, a: usize, b: usize) {
+        self.core.swap_indices(a, b)
+    }
+}
+
+/// An iterator over the keys of a `IndexMap`.
+///
+/// This `struct` is created by the [`keys`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`keys`]: struct.IndexMap.html#method.keys
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Keys<'a, K, V> {
+    iter: SliceIter<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for Keys<'a, K, V> {
+    type Item = &'a K;
+
+    iterator_methods!(Bucket::key_ref);
+}
+
+impl<K, V> DoubleEndedIterator for Keys<'_, K, V> {
+    double_ended_iterator_methods!(Bucket::key_ref);
+}
+
+impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for Keys<'_, K, V> {}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Keys<'_, K, V> {
+    fn clone(&self) -> Self {
+        Keys {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<K: fmt::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 owning iterator over the keys of a `IndexMap`.
+///
+/// This `struct` is created by the [`into_keys`] method on [`IndexMap`].
+/// See its documentation for more.
+///
+/// [`IndexMap`]: struct.IndexMap.html
+/// [`into_keys`]: struct.IndexMap.html#method.into_keys
+pub struct IntoKeys<K, V> {
+    iter: vec::IntoIter<Bucket<K, V>>,
+}
+
+impl<K, V> Iterator for IntoKeys<K, V> {
+    type Item = K;
+
+    iterator_methods!(Bucket::key);
+}
+
+impl<K, V> DoubleEndedIterator for IntoKeys<K, V> {
+    double_ended_iterator_methods!(Bucket::key);
+}
+
+impl<K, V> ExactSizeIterator for IntoKeys<K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for IntoKeys<K, V> {}
+
+impl<K: fmt::Debug, V> fmt::Debug for IntoKeys<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::key_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+/// An iterator over the values of a `IndexMap`.
+///
+/// This `struct` is created by the [`values`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`values`]: struct.IndexMap.html#method.values
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Values<'a, K, V> {
+    iter: SliceIter<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for Values<'a, K, V> {
+    type Item = &'a V;
+
+    iterator_methods!(Bucket::value_ref);
+}
+
+impl<K, V> DoubleEndedIterator for Values<'_, K, V> {
+    double_ended_iterator_methods!(Bucket::value_ref);
+}
+
+impl<K, V> ExactSizeIterator for Values<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for Values<'_, K, V> {}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Values<'_, K, V> {
+    fn clone(&self) -> Self {
+        Values {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<K, V: fmt::Debug> fmt::Debug for Values<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_list().entries(self.clone()).finish()
+    }
+}
+
+/// A mutable iterator over the values of a `IndexMap`.
+///
+/// This `struct` is created by the [`values_mut`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`values_mut`]: struct.IndexMap.html#method.values_mut
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct ValuesMut<'a, K, V> {
+    iter: SliceIterMut<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
+    type Item = &'a mut V;
+
+    iterator_methods!(Bucket::value_mut);
+}
+
+impl<K, V> DoubleEndedIterator for ValuesMut<'_, K, V> {
+    double_ended_iterator_methods!(Bucket::value_mut);
+}
+
+impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}
+
+impl<K, V: fmt::Debug> fmt::Debug for ValuesMut<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::value_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+/// An owning iterator over the values of a `IndexMap`.
+///
+/// This `struct` is created by the [`into_values`] method on [`IndexMap`].
+/// See its documentation for more.
+///
+/// [`IndexMap`]: struct.IndexMap.html
+/// [`into_values`]: struct.IndexMap.html#method.into_values
+pub struct IntoValues<K, V> {
+    iter: vec::IntoIter<Bucket<K, V>>,
+}
+
+impl<K, V> Iterator for IntoValues<K, V> {
+    type Item = V;
+
+    iterator_methods!(Bucket::value);
+}
+
+impl<K, V> DoubleEndedIterator for IntoValues<K, V> {
+    double_ended_iterator_methods!(Bucket::value);
+}
+
+impl<K, V> ExactSizeIterator for IntoValues<K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for IntoValues<K, V> {}
+
+impl<K, V: fmt::Debug> fmt::Debug for IntoValues<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::value_ref);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+/// An iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`iter`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`iter`]: struct.IndexMap.html#method.iter
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Iter<'a, K, V> {
+    iter: SliceIter<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for Iter<'a, K, V> {
+    type Item = (&'a K, &'a V);
+
+    iterator_methods!(Bucket::refs);
+}
+
+impl<K, V> DoubleEndedIterator for Iter<'_, K, V> {
+    double_ended_iterator_methods!(Bucket::refs);
+}
+
+impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for Iter<'_, K, V> {}
+
+// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
+impl<K, V> Clone for Iter<'_, K, V> {
+    fn clone(&self) -> Self {
+        Iter {
+            iter: self.iter.clone(),
+        }
+    }
+}
+
+impl<K: fmt::Debug, V: fmt::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 `IndexMap`.
+///
+/// This `struct` is created by the [`iter_mut`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`iter_mut`]: struct.IndexMap.html#method.iter_mut
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct IterMut<'a, K, V> {
+    iter: SliceIterMut<'a, Bucket<K, V>>,
+}
+
+impl<'a, K, V> Iterator for IterMut<'a, K, V> {
+    type Item = (&'a K, &'a mut V);
+
+    iterator_methods!(Bucket::ref_mut);
+}
+
+impl<K, V> DoubleEndedIterator for IterMut<'_, K, V> {
+    double_ended_iterator_methods!(Bucket::ref_mut);
+}
+
+impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for IterMut<'_, K, V> {}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IterMut<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::refs);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+/// An owning iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`into_iter`] method on [`IndexMap`]
+/// (provided by the `IntoIterator` trait). See its documentation for more.
+///
+/// [`into_iter`]: struct.IndexMap.html#method.into_iter
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct IntoIter<K, V> {
+    iter: vec::IntoIter<Bucket<K, V>>,
+}
+
+impl<K, V> Iterator for IntoIter<K, V> {
+    type Item = (K, V);
+
+    iterator_methods!(Bucket::key_value);
+}
+
+impl<K, V> DoubleEndedIterator for IntoIter<K, V> {
+    double_ended_iterator_methods!(Bucket::key_value);
+}
+
+impl<K, V> ExactSizeIterator for IntoIter<K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for IntoIter<K, V> {}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for IntoIter<K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::refs);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+/// A draining iterator over the entries of a `IndexMap`.
+///
+/// This `struct` is created by the [`drain`] method on [`IndexMap`]. See its
+/// documentation for more.
+///
+/// [`drain`]: struct.IndexMap.html#method.drain
+/// [`IndexMap`]: struct.IndexMap.html
+pub struct Drain<'a, K, V> {
+    pub(crate) iter: vec::Drain<'a, Bucket<K, V>>,
+}
+
+impl<K, V> Iterator for Drain<'_, K, V> {
+    type Item = (K, V);
+
+    iterator_methods!(Bucket::key_value);
+}
+
+impl<K, V> DoubleEndedIterator for Drain<'_, K, V> {
+    double_ended_iterator_methods!(Bucket::key_value);
+}
+
+impl<K, V> ExactSizeIterator for Drain<'_, K, V> {
+    fn len(&self) -> usize {
+        self.iter.len()
+    }
+}
+
+impl<K, V> FusedIterator for Drain<'_, K, V> {}
+
+impl<K: fmt::Debug, V: fmt::Debug> fmt::Debug for Drain<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let iter = self.iter.as_slice().iter().map(Bucket::refs);
+        f.debug_list().entries(iter).finish()
+    }
+}
+
+impl<'a, K, V, S> IntoIterator for &'a IndexMap<K, V, S> {
+    type Item = (&'a K, &'a V);
+    type IntoIter = Iter<'a, K, V>;
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+impl<'a, K, V, S> IntoIterator for &'a mut IndexMap<K, V, S> {
+    type Item = (&'a K, &'a mut V);
+    type IntoIter = IterMut<'a, K, V>;
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter_mut()
+    }
+}
+
+impl<K, V, S> IntoIterator for IndexMap<K, V, S> {
+    type Item = (K, V);
+    type IntoIter = IntoIter<K, V>;
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter {
+            iter: self.into_entries().into_iter(),
+        }
+    }
+}
+
+/// Access `IndexMap` values corresponding to a key.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_uppercase());
+/// }
+/// assert_eq!(map["lorem"], "LOREM");
+/// assert_eq!(map["ipsum"], "IPSUM");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// println!("{:?}", map["bar"]); // panics!
+/// ```
+impl<K, V, Q: ?Sized, S> Index<&Q> for IndexMap<K, V, S>
+where
+    Q: Hash + Equivalent<K>,
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    type Output = V;
+
+    /// Returns a reference to the value corresponding to the supplied `key`.
+    ///
+    /// ***Panics*** if `key` is not present in the map.
+    fn index(&self, key: &Q) -> &V {
+        self.get(key).expect("IndexMap: key not found")
+    }
+}
+
+/// Access `IndexMap` values corresponding to a key.
+///
+/// Mutable indexing allows changing / updating values of key-value
+/// pairs that are already present.
+///
+/// You can **not** insert new pairs with index syntax, use `.insert()`.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_string());
+/// }
+/// let lorem = &mut map["lorem"];
+/// assert_eq!(lorem, "Lorem");
+/// lorem.retain(char::is_lowercase);
+/// assert_eq!(map["lorem"], "orem");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// map["bar"] = 1; // panics!
+/// ```
+impl<K, V, Q: ?Sized, S> IndexMut<&Q> for IndexMap<K, V, S>
+where
+    Q: Hash + Equivalent<K>,
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    /// Returns a mutable reference to the value corresponding to the supplied `key`.
+    ///
+    /// ***Panics*** if `key` is not present in the map.
+    fn index_mut(&mut self, key: &Q) -> &mut V {
+        self.get_mut(key).expect("IndexMap: key not found")
+    }
+}
+
+/// Access `IndexMap` values at indexed positions.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_uppercase());
+/// }
+/// assert_eq!(map[0], "LOREM");
+/// assert_eq!(map[1], "IPSUM");
+/// map.reverse();
+/// assert_eq!(map[0], "AMET");
+/// assert_eq!(map[1], "SIT");
+/// map.sort_keys();
+/// assert_eq!(map[0], "AMET");
+/// assert_eq!(map[1], "DOLOR");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// println!("{:?}", map[10]); // panics!
+/// ```
+impl<K, V, S> Index<usize> for IndexMap<K, V, S> {
+    type Output = V;
+
+    /// Returns a reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index(&self, index: usize) -> &V {
+        self.get_index(index)
+            .expect("IndexMap: index out of bounds")
+            .1
+    }
+}
+
+/// Access `IndexMap` values at indexed positions.
+///
+/// Mutable indexing allows changing / updating indexed values
+/// that are already present.
+///
+/// You can **not** insert new values with index syntax, use `.insert()`.
+///
+/// # Examples
+///
+/// ```
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// for word in "Lorem ipsum dolor sit amet".split_whitespace() {
+///     map.insert(word.to_lowercase(), word.to_string());
+/// }
+/// let lorem = &mut map[0];
+/// assert_eq!(lorem, "Lorem");
+/// lorem.retain(char::is_lowercase);
+/// assert_eq!(map["lorem"], "orem");
+/// ```
+///
+/// ```should_panic
+/// use indexmap::IndexMap;
+///
+/// let mut map = IndexMap::new();
+/// map.insert("foo", 1);
+/// map[10] = 1; // panics!
+/// ```
+impl<K, V, S> IndexMut<usize> for IndexMap<K, V, S> {
+    /// Returns a mutable reference to the value at the supplied `index`.
+    ///
+    /// ***Panics*** if `index` is out of bounds.
+    fn index_mut(&mut self, index: usize) -> &mut V {
+        self.get_index_mut(index)
+            .expect("IndexMap: index out of bounds")
+            .1
+    }
+}
+
+impl<K, V, S> FromIterator<(K, V)> for IndexMap<K, V, S>
+where
+    K: Hash + Eq,
+    S: BuildHasher + Default,
+{
+    /// Create an `IndexMap` from the sequence of key-value pairs in the
+    /// iterable.
+    ///
+    /// `from_iter` uses the same logic as `extend`. See
+    /// [`extend`](#method.extend) for more details.
+    fn from_iter<I: IntoIterator<Item = (K, V)>>(iterable: I) -> Self {
+        let iter = iterable.into_iter();
+        let (low, _) = iter.size_hint();
+        let mut map = Self::with_capacity_and_hasher(low, <_>::default());
+        map.extend(iter);
+        map
+    }
+}
+
+#[cfg(has_std)]
+impl<K, V, const N: usize> From<[(K, V); N]> for IndexMap<K, V, RandomState>
+where
+    K: Hash + Eq,
+{
+    /// # Examples
+    ///
+    /// ```
+    /// use indexmap::IndexMap;
+    ///
+    /// let map1 = IndexMap::from([(1, 2), (3, 4)]);
+    /// let map2: IndexMap<_, _> = [(1, 2), (3, 4)].into();
+    /// assert_eq!(map1, map2);
+    /// ```
+    fn from(arr: [(K, V); N]) -> Self {
+        Self::from_iter(arr)
+    }
+}
+
+impl<K, V, S> Extend<(K, V)> for IndexMap<K, V, S>
+where
+    K: Hash + Eq,
+    S: BuildHasher,
+{
+    /// Extend the map with all key-value pairs in the iterable.
+    ///
+    /// This is equivalent to calling [`insert`](#method.insert) for each of
+    /// them in order, which means that for keys that already existed
+    /// in the map, their value is updated but it keeps the existing order.
+    ///
+    /// New keys are inserted in the order they appear in the sequence. If
+    /// equivalents of a key occur more than once, the last corresponding value
+    /// prevails.
+    fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iterable: I) {
+        // (Note: this is a copy of `std`/`hashbrown`'s reservation logic.)
+        // 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 = iterable.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);
+        });
+    }
+}
+
+impl<'a, K, V, S> Extend<(&'a K, &'a V)> for IndexMap<K, V, S>
+where
+    K: Hash + Eq + Copy,
+    V: Copy,
+    S: BuildHasher,
+{
+    /// Extend the map with all key-value pairs in the iterable.
+    ///
+    /// See the first extend method for more details.
+    fn extend<I: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iterable: I) {
+        self.extend(iterable.into_iter().map(|(&key, &value)| (key, value)));
+    }
+}
+
+impl<K, V, S> Default for IndexMap<K, V, S>
+where
+    S: Default,
+{
+    /// Return an empty `IndexMap`
+    fn default() -> Self {
+        Self::with_capacity_and_hasher(0, S::default())
+    }
+}
+
+impl<K, V1, S1, V2, S2> PartialEq<IndexMap<K, V2, S2>> for IndexMap<K, V1, S1>
+where
+    K: Hash + Eq,
+    V1: PartialEq<V2>,
+    S1: BuildHasher,
+    S2: BuildHasher,
+{
+    fn eq(&self, other: &IndexMap<K, V2, S2>) -> 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> Eq for IndexMap<K, V, S>
+where
+    K: Eq + Hash,
+    V: Eq,
+    S: BuildHasher,
+{
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::string::String;
+
+    #[test]
+    fn it_works() {
+        let mut map = IndexMap::new();
+        assert_eq!(map.is_empty(), true);
+        map.insert(1, ());
+        map.insert(1, ());
+        assert_eq!(map.len(), 1);
+        assert!(map.get(&1).is_some());
+        assert_eq!(map.is_empty(), false);
+    }
+
+    #[test]
+    fn new() {
+        let map = IndexMap::<String, String>::new();
+        println!("{:?}", map);
+        assert_eq!(map.capacity(), 0);
+        assert_eq!(map.len(), 0);
+        assert_eq!(map.is_empty(), true);
+    }
+
+    #[test]
+    fn insert() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5];
+        let not_present = [1, 3, 6, 9, 10];
+        let mut map = IndexMap::with_capacity(insert.len());
+
+        for (i, &elt) in insert.iter().enumerate() {
+            assert_eq!(map.len(), i);
+            map.insert(elt, elt);
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.get(&elt), Some(&elt));
+            assert_eq!(map[&elt], elt);
+        }
+        println!("{:?}", map);
+
+        for &elt in &not_present {
+            assert!(map.get(&elt).is_none());
+        }
+    }
+
+    #[test]
+    fn insert_full() {
+        let insert = vec![9, 2, 7, 1, 4, 6, 13];
+        let present = vec![1, 6, 2];
+        let mut map = IndexMap::with_capacity(insert.len());
+
+        for (i, &elt) in insert.iter().enumerate() {
+            assert_eq!(map.len(), i);
+            let (index, existing) = map.insert_full(elt, elt);
+            assert_eq!(existing, None);
+            assert_eq!(Some(index), map.get_full(&elt).map(|x| x.0));
+            assert_eq!(map.len(), i + 1);
+        }
+
+        let len = map.len();
+        for &elt in &present {
+            let (index, existing) = map.insert_full(elt, elt);
+            assert_eq!(existing, Some(elt));
+            assert_eq!(Some(index), map.get_full(&elt).map(|x| x.0));
+            assert_eq!(map.len(), len);
+        }
+    }
+
+    #[test]
+    fn insert_2() {
+        let mut map = IndexMap::with_capacity(16);
+
+        let mut keys = vec![];
+        keys.extend(0..16);
+        keys.extend(if cfg!(miri) { 32..64 } else { 128..267 });
+
+        for &i in &keys {
+            let old_map = map.clone();
+            map.insert(i, ());
+            for key in old_map.keys() {
+                if map.get(key).is_none() {
+                    println!("old_map: {:?}", old_map);
+                    println!("map: {:?}", map);
+                    panic!("did not find {} in map", key);
+                }
+            }
+        }
+
+        for &i in &keys {
+            assert!(map.get(&i).is_some(), "did not find {}", i);
+        }
+    }
+
+    #[test]
+    fn insert_order() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut map = IndexMap::new();
+
+        for &elt in &insert {
+            map.insert(elt, ());
+        }
+
+        assert_eq!(map.keys().count(), map.len());
+        assert_eq!(map.keys().count(), insert.len());
+        for (a, b) in insert.iter().zip(map.keys()) {
+            assert_eq!(a, b);
+        }
+        for (i, k) in (0..insert.len()).zip(map.keys()) {
+            assert_eq!(map.get_index(i).unwrap().0, k);
+        }
+    }
+
+    #[test]
+    fn grow() {
+        let insert = [0, 4, 2, 12, 8, 7, 11];
+        let not_present = [1, 3, 6, 9, 10];
+        let mut map = IndexMap::with_capacity(insert.len());
+
+        for (i, &elt) in insert.iter().enumerate() {
+            assert_eq!(map.len(), i);
+            map.insert(elt, elt);
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.get(&elt), Some(&elt));
+            assert_eq!(map[&elt], elt);
+        }
+
+        println!("{:?}", map);
+        for &elt in &insert {
+            map.insert(elt * 10, elt);
+        }
+        for &elt in &insert {
+            map.insert(elt * 100, elt);
+        }
+        for (i, &elt) in insert.iter().cycle().enumerate().take(100) {
+            map.insert(elt * 100 + i as i32, elt);
+        }
+        println!("{:?}", map);
+        for &elt in &not_present {
+            assert!(map.get(&elt).is_none());
+        }
+    }
+
+    #[test]
+    fn reserve() {
+        let mut map = IndexMap::<usize, usize>::new();
+        assert_eq!(map.capacity(), 0);
+        map.reserve(100);
+        let capacity = map.capacity();
+        assert!(capacity >= 100);
+        for i in 0..capacity {
+            assert_eq!(map.len(), i);
+            map.insert(i, i * i);
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.capacity(), capacity);
+            assert_eq!(map.get(&i), Some(&(i * i)));
+        }
+        map.insert(capacity, std::usize::MAX);
+        assert_eq!(map.len(), capacity + 1);
+        assert!(map.capacity() > capacity);
+        assert_eq!(map.get(&capacity), Some(&std::usize::MAX));
+    }
+
+    #[test]
+    fn shrink_to_fit() {
+        let mut map = IndexMap::<usize, usize>::new();
+        assert_eq!(map.capacity(), 0);
+        for i in 0..100 {
+            assert_eq!(map.len(), i);
+            map.insert(i, i * i);
+            assert_eq!(map.len(), i + 1);
+            assert!(map.capacity() >= i + 1);
+            assert_eq!(map.get(&i), Some(&(i * i)));
+            map.shrink_to_fit();
+            assert_eq!(map.len(), i + 1);
+            assert_eq!(map.capacity(), i + 1);
+            assert_eq!(map.get(&i), Some(&(i * i)));
+        }
+    }
+
+    #[test]
+    fn remove() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut map = IndexMap::new();
+
+        for &elt in &insert {
+            map.insert(elt, elt);
+        }
+
+        assert_eq!(map.keys().count(), map.len());
+        assert_eq!(map.keys().count(), insert.len());
+        for (a, b) in insert.iter().zip(map.keys()) {
+            assert_eq!(a, b);
+        }
+
+        let remove_fail = [99, 77];
+        let remove = [4, 12, 8, 7];
+
+        for &key in &remove_fail {
+            assert!(map.swap_remove_full(&key).is_none());
+        }
+        println!("{:?}", map);
+        for &key in &remove {
+            //println!("{:?}", map);
+            let index = map.get_full(&key).unwrap().0;
+            assert_eq!(map.swap_remove_full(&key), Some((index, key, key)));
+        }
+        println!("{:?}", map);
+
+        for key in &insert {
+            assert_eq!(map.get(key).is_some(), !remove.contains(key));
+        }
+        assert_eq!(map.len(), insert.len() - remove.len());
+        assert_eq!(map.keys().count(), insert.len() - remove.len());
+    }
+
+    #[test]
+    fn remove_to_empty() {
+        let mut map = indexmap! { 0 => 0, 4 => 4, 5 => 5 };
+        map.swap_remove(&5).unwrap();
+        map.swap_remove(&4).unwrap();
+        map.swap_remove(&0).unwrap();
+        assert!(map.is_empty());
+    }
+
+    #[test]
+    fn swap_remove_index() {
+        let insert = [0, 4, 2, 12, 8, 7, 11, 5, 3, 17, 19, 22, 23];
+        let mut map = IndexMap::new();
+
+        for &elt in &insert {
+            map.insert(elt, elt * 2);
+        }
+
+        let mut vector = insert.to_vec();
+        let remove_sequence = &[3, 3, 10, 4, 5, 4, 3, 0, 1];
+
+        // check that the same swap remove sequence on vec and map
+        // have the same result.
+        for &rm in remove_sequence {
+            let out_vec = vector.swap_remove(rm);
+            let (out_map, _) = map.swap_remove_index(rm).unwrap();
+            assert_eq!(out_vec, out_map);
+        }
+        assert_eq!(vector.len(), map.len());
+        for (a, b) in vector.iter().zip(map.keys()) {
+            assert_eq!(a, b);
+        }
+    }
+
+    #[test]
+    fn partial_eq_and_eq() {
+        let mut map_a = IndexMap::new();
+        map_a.insert(1, "1");
+        map_a.insert(2, "2");
+        let mut map_b = map_a.clone();
+        assert_eq!(map_a, map_b);
+        map_b.swap_remove(&1);
+        assert_ne!(map_a, map_b);
+
+        let map_c: IndexMap<_, String> = map_b.into_iter().map(|(k, v)| (k, v.into())).collect();
+        assert_ne!(map_a, map_c);
+        assert_ne!(map_c, map_a);
+    }
+
+    #[test]
+    fn extend() {
+        let mut map = IndexMap::new();
+        map.extend(vec![(&1, &2), (&3, &4)]);
+        map.extend(vec![(5, 6)]);
+        assert_eq!(
+            map.into_iter().collect::<Vec<_>>(),
+            vec![(1, 2), (3, 4), (5, 6)]
+        );
+    }
+
+    #[test]
+    fn entry() {
+        let mut map = IndexMap::new();
+
+        map.insert(1, "1");
+        map.insert(2, "2");
+        {
+            let e = map.entry(3);
+            assert_eq!(e.index(), 2);
+            let e = e.or_insert("3");
+            assert_eq!(e, &"3");
+        }
+
+        let e = map.entry(2);
+        assert_eq!(e.index(), 1);
+        assert_eq!(e.key(), &2);
+        match e {
+            Entry::Occupied(ref e) => assert_eq!(e.get(), &"2"),
+            Entry::Vacant(_) => panic!(),
+        }
+        assert_eq!(e.or_insert("4"), &"2");
+    }
+
+    #[test]
+    fn entry_and_modify() {
+        let mut map = IndexMap::new();
+
+        map.insert(1, "1");
+        map.entry(1).and_modify(|x| *x = "2");
+        assert_eq!(Some(&"2"), map.get(&1));
+
+        map.entry(2).and_modify(|x| *x = "doesn't exist");
+        assert_eq!(None, map.get(&2));
+    }
+
+    #[test]
+    fn entry_or_default() {
+        let mut map = IndexMap::new();
+
+        #[derive(Debug, PartialEq)]
+        enum TestEnum {
+            DefaultValue,
+            NonDefaultValue,
+        }
+
+        impl Default for TestEnum {
+            fn default() -> Self {
+                TestEnum::DefaultValue
+            }
+        }
+
+        map.insert(1, TestEnum::NonDefaultValue);
+        assert_eq!(&mut TestEnum::NonDefaultValue, map.entry(1).or_default());
+
+        assert_eq!(&mut TestEnum::DefaultValue, map.entry(2).or_default());
+    }
+
+    #[test]
+    fn occupied_entry_key() {
+        // These keys match hash and equality, but their addresses are distinct.
+        let (k1, k2) = (&mut 1, &mut 1);
+        let k1_ptr = k1 as *const i32;
+        let k2_ptr = k2 as *const i32;
+        assert_ne!(k1_ptr, k2_ptr);
+
+        let mut map = IndexMap::new();
+        map.insert(k1, "value");
+        match map.entry(k2) {
+            Entry::Occupied(ref e) => {
+                // `OccupiedEntry::key` should reference the key in the map,
+                // not the key that was used to find the entry.
+                let ptr = *e.key() as *const i32;
+                assert_eq!(ptr, k1_ptr);
+                assert_ne!(ptr, k2_ptr);
+            }
+            Entry::Vacant(_) => panic!(),
+        }
+    }
+
+    #[test]
+    fn keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = 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 into_keys() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = vec.into_iter().collect();
+        let keys: Vec<i32> = map.into_keys().collect();
+        assert_eq!(keys.len(), 3);
+        assert!(keys.contains(&1));
+        assert!(keys.contains(&2));
+        assert!(keys.contains(&3));
+    }
+
+    #[test]
+    fn values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = 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 values_mut() {
+        let vec = vec![(1, 1), (2, 2), (3, 3)];
+        let mut map: IndexMap<_, _> = 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 into_values() {
+        let vec = vec![(1, 'a'), (2, 'b'), (3, 'c')];
+        let map: IndexMap<_, _> = vec.into_iter().collect();
+        let values: Vec<char> = map.into_values().collect();
+        assert_eq!(values.len(), 3);
+        assert!(values.contains(&'a'));
+        assert!(values.contains(&'b'));
+        assert!(values.contains(&'c'));
+    }
+
+    #[test]
+    #[cfg(has_std)]
+    fn from_array() {
+        let map = IndexMap::from([(1, 2), (3, 4)]);
+        let mut expected = IndexMap::new();
+        expected.insert(1, 2);
+        expected.insert(3, 4);
+
+        assert_eq!(map, expected)
+    }
+}