hashslab 0.5.2

//! A hash map with indexes
use core::{
    fmt,
    hash::{BuildHasher, Hash},
    mem,
    ops::{Index, IndexMut},
};

#[cfg(feature = "std")]
use std::hash::RandomState;

use hashbrown::{hash_table, Equivalent, HashTable};
use slab::Slab;

use crate::{TryReserveError, ValueData};

use super::KeyData;

mod keys;
pub use keys::{FullKeys, Indices, IntoKeys, Keys};

mod values;
pub use values::{IntoValues, Values, ValuesMut};

mod iter;
pub use iter::{IntoFullIter, IntoIter, Iter, IterFull, IterFullMut, IterMut};

mod drain;
pub use drain::{Drain, DrainFull};

mod entry;
pub use entry::{Entry, OccupiedEntry, VacantEntry};

#[cfg(test)]
mod tests;

/// A hash map with indexes
///
/// The interface is closely compatible with the [`IndexMap`].
///
/// # Indices
///
/// [`HashSlabMap`] returns the index ([`usize`]) when storing the value. It
/// is important to note that index may be reused. In other words, once a value
/// associated with a given index is removed from a hashslab, that index may be
/// returned from future calls to insert. 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
///
/// Standard [`HashMap`] usage:
/// ```
/// # use hashslab::HashSlabMap;
/// // Type inference lets us omit an explicit type signature (which
/// // would be `HashSlabMap<String, String>` in this example).
/// let mut book_reviews = HashSlabMap::new();
///
/// // Review some books.
/// book_reviews.insert(
///     "Adventures of Huckleberry Finn".to_string(),
///     "My favorite book.".to_string(),
/// );
/// book_reviews.insert(
///     "Grimms' Fairy Tales".to_string(),
///     "Masterpiece.".to_string(),
/// );
/// book_reviews.insert(
///     "Pride and Prejudice".to_string(),
///     "Very enjoyable.".to_string(),
/// );
/// book_reviews.insert(
///     "The Adventures of Sherlock Holmes".to_string(),
///     "Eye lyked it alot.".to_string(),
/// );
///
/// // Check for a specific one.
/// // When collections store owned values (String), they can still be
/// // queried using references (&str).
/// if !book_reviews.contains_key("Les Misérables") {
///     println!("We've got {} reviews, but Les Misérables ain't one.",
///              book_reviews.len());
/// }
///
/// // oops, this review has a lot of spelling mistakes, let's delete it.
/// book_reviews.remove("The Adventures of Sherlock Holmes");
///
/// // Look up the values associated with some keys.
/// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
/// for &book in &to_find {
///     match book_reviews.get(book) {
///         Some(review) => println!("{}: {}", book, review),
///         None => println!("{} is unreviewed.", book)
///     }
/// }
///
/// // Look up the value for a key (will panic if the key is not found).
/// println!("Review for Jane: {}", book_reviews["Pride and Prejudice"]);
///
/// // Iterate over everything.
/// for (book, review) in &book_reviews {
///     println!("{}: \"{}\"", book, review);
/// }
/// ```
///
/// With indices:
/// ```
/// # use hashslab::HashSlabMap;
/// // count the frequency of each letter in a sentence.
/// let mut letters = HashSlabMap::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.get_index_of(&'a'), Some(0));
/// assert_eq!(letters.get_index(1), Some((&' ', &4)));
/// assert_eq!(letters.get(&'y'), None);
/// ```
///
/// [`HashMap`]: https://doc.rust-lang.org/std/collections/struct.HashMap.html
/// [`IndexMap`]: https://docs.rs/indexmap/latest/indexmap/map/struct.IndexMap.html
/// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
/// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
/// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
/// [`RefCell`]: https://doc.rust-lang.org/std/cell/struct.RefCell.html
/// [`Cell`]: https://doc.rust-lang.org/std/cell/struct.Cell.html
/// [`default`]: #method.default
/// [`with_hasher`]: #method.with_hasher
/// [`with_capacity_and_hasher`]: #method.with_capacity_and_hasher
#[cfg(feature = "std")]
pub struct HashSlabMap<K, V, S = RandomState> {
    pub(crate) table: HashTable<KeyData<K>>,
    pub(crate) slab: Slab<ValueData<V>>,
    pub(crate) builder: S,
}

#[cfg(not(feature = "std"))]
pub struct HashSlabMap<K, V, S> {
    table: HashTable<KeyData<K>>,
    slab: Slab<ValueData<V>>,
    builder: S,
}

#[cfg(feature = "std")]
#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
impl<K, V> HashSlabMap<K, V> {
    /// Creates an empty `HashSlabMap`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut map: HashSlabMap<&str, i32> = HashSlabMap::new();
    /// assert_eq!(map.len(), 0);
    /// assert_eq!(map.capacity(), 0);
    /// ```
    #[inline]
    pub fn new() -> Self {
        Self::with_capacity(0)
    }

    /// Creates an empty `HashSlabMap` with the specified capacity.
    ///
    /// The hash map will be able to hold at least `capacity` elements without
    /// reallocating. If `capacity` is 0, the hash map will not allocate.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut map: HashSlabMap<&str, i32> = HashSlabMap::with_capacity(10);
    /// assert_eq!(map.len(), 0);
    /// assert!(map.capacity() >= 10);
    /// ```
    #[inline]
    pub fn with_capacity(n: usize) -> Self {
        Self::with_capacity_and_hasher(n, Default::default())
    }
}

impl<K, V, S> HashSlabMap<K, V, S> {
    /// Creates an empty `HashSlabMap` with the specified capacity, using `hash_builder`
    /// to hash the keys.
    ///
    /// The hash map will be able to hold at least `capacity` elements without
    /// reallocating. If `capacity` is 0, the hash map will not allocate.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// use std::hash::RandomState;
    ///
    /// let s = RandomState::new();
    /// let mut map = HashSlabMap::with_capacity_and_hasher(10, s);
    /// assert_eq!(map.len(), 0);
    /// assert!(map.capacity() >= 10);
    ///
    /// map.insert(1, 2);
    /// ```
    #[inline]
    pub fn with_capacity_and_hasher(n: usize, builder: S) -> Self {
        Self {
            table: HashTable::with_capacity(n),
            slab: Slab::with_capacity(n),
            builder,
        }
    }

    /// Create a new map with `hash_builder`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let s = std::hash::RandomState::new();
    /// let mut map = HashSlabMap::with_hasher(s);
    /// assert_eq!(map.len(), 0);
    /// assert_eq!(map.capacity(), 0);
    ///
    /// map.insert(1, 2);
    /// ```
    pub const fn with_hasher(builder: S) -> Self {
        Self {
            table: HashTable::new(),
            slab: Slab::new(),
            builder,
        }
    }

    /// Return the number of values the hashslab can store without reallocating.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let map = HashSlabMap::<(), ()>::with_capacity(100);
    /// assert!(map.capacity() >= 100);
    /// ```
    pub fn capacity(&self) -> usize {
        self.table.capacity().min(self.slab.capacity())
    }

    /// Returns a reference to the map's [`BuildHasher`].
    ///
    /// [`BuildHasher`]: https://doc.rust-lang.org/std/hash/trait.BuildHasher.html
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// use std::hash::{RandomState, BuildHasherDefault};
    /// use fnv::{FnvBuildHasher, FnvHasher};
    ///
    /// let map = HashSlabMap::<(), ()>::new();
    /// let hasher: &RandomState = map.hasher();
    ///
    /// let s = FnvBuildHasher::default();
    /// let mut map = HashSlabMap::with_hasher(s);
    /// map.insert(1, 2);
    /// let hasher: &BuildHasherDefault<FnvHasher> = map.hasher();
    /// ```
    pub fn hasher(&self) -> &S {
        &self.builder
    }

    /// Return the number of key-value pairs in the map.
    #[inline]
    pub fn len(&self) -> usize {
        debug_assert_eq!(
            self.table.len(),
            self.slab.len(),
            "Number of entries in HashTable and Slab should be equal"
        );
        self.table.len()
    }

    /// Returns true if the map contains no elements.
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// An iterator over the index-key-value triples in arbitrary order.  
    /// The iterator element type is `(usize, &'a K, &'a V)`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    /// assert_eq!(map.len(), 3);
    /// let mut vec: Vec<(usize, &str, i32)> = Vec::new();
    ///
    /// for (idx, key, val) in map.iter_full() {
    ///     println!("idx: {idx}, key: {key} val: {val}");
    ///     vec.push((idx, *key, *val));
    /// }
    ///
    /// // The `IterFull` 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, [(0, "a", 1), (1, "b", 2), (2, "c", 3)]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn iter_full(&self) -> IterFull<'_, K, V> {
        IterFull::new(self.table.iter(), &self.slab)
    }

    /// An iterator visiting all key-value pairs in arbitrary order.  
    /// The iterator element type is `(&'a K, &'a V)`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    /// assert_eq!(map.len(), 3);
    /// let mut vec: Vec<(&str, i32)> = Vec::new();
    ///
    /// for (key, val) in map.iter() {
    ///     println!("key: {} val: {}", key, val);
    ///     vec.push((*key, *val));
    /// }
    ///
    /// // The `Iter` iterator produces items in arbitrary order, so the
    /// // items must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3)]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn iter(&self) -> Iter<'_, K, V> {
        Iter::new(self.iter_full())
    }

    /// An iterator visiting all index-key-value triple in arbitrary order,
    /// with mutable references to the values.  
    /// The iterator element type is `(usize, &'a K, &'a mut V)`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// assert_eq!(map.len(), 3);
    /// 
    /// let mut vec: Vec<(usize, &str, i32)> = Vec::new();
    ///
    /// for (idx, key, val) in map.iter_full_mut() {
    ///     assert_eq!(idx + 1, *val as usize);
    ///     // Update value
    ///     *val *= 2;
    ///     println!("idx: {idx}, key: {key} val: {val}");
    ///     vec.push((idx, *key, *val));
    /// }
    ///
    /// // The `IterFullMut` 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, [(0, "a", 2), (1, "b", 4), (2, "c", 6)]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn iter_full_mut(&mut self) -> IterFullMut<'_, K, V> {
        IterFullMut::new(self.table.iter(), &mut self.slab)
    }

    /// An iterator visiting all key-value pairs in arbitrary order, with mutable references to the values.  
    /// The iterator element type is `(&'a K, &'a mut V)`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// // Update all values
    /// for (_, val) in map.iter_mut() {
    ///     *val *= 2;
    /// }
    ///
    /// assert_eq!(map.len(), 3);
    /// let mut vec: Vec<(&str, i32)> = Vec::new();
    ///
    /// for (key, val) in &map {
    ///     println!("key: {} val: {}", key, val);
    ///     vec.push((*key, *val));
    /// }
    ///
    /// // The `Iter` iterator produces items in arbitrary order, so the
    /// // items must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [("a", 2), ("b", 4), ("c", 6)]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn iter_mut(&mut self) -> IterMut<'_, K, V>
    where
        K: Clone,
    {
        IterMut::new(self.iter_full_mut())
    }

    /// Creates a consuming iterator, that is, one that moves each index-key-value
    /// pair out of the map in arbitrary order. The map cannot be used after
    /// calling this.  
    /// The iterator element type is `(usize, K, V)`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let map: HashSlabMap<_, _> = [("a", 1), ("b", 2), ("c", 3)].into();
    ///
    /// // Not possible with .iter_full()
    /// let mut vec: Vec<(usize, &str, i32)> = map.into_full_iter().collect();
    /// // The `IntoFullIter` 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, [(0, "a", 1), (1, "b", 2), (2, "c", 3)]);
    /// ```
    pub fn into_full_iter(self) -> IntoFullIter<K, V> {
        IntoFullIter::new(self.table.into_iter(), self.slab)
    }

    /// An iterator visiting index-keys pairs in arbitrary order.  
    /// The iterator element type is `&'a K`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    /// assert_eq!(map.len(), 3);
    /// let mut vec: Vec<(usize, &str)> = Vec::new();
    ///
    /// for (idx, key) in map.full_keys() {
    ///     println!("idx: {idx}, key: {key}");
    ///     vec.push((idx, *key));
    /// }
    ///
    /// // The `Keys` iterator produces keys in arbitrary order, so the
    /// // keys must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [(0, "a"), (1, "b"), (2, "c")]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn full_keys(&self) -> FullKeys<'_, K> {
        FullKeys::new(self.table.iter())
    }

    /// An iterator visiting all keys in arbitrary order.  
    /// The iterator element type is `&'a K`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    /// assert_eq!(map.len(), 3);
    /// let mut vec: Vec<&str> = Vec::new();
    ///
    /// for key in map.keys() {
    ///     println!("{}", key);
    ///     vec.push(*key);
    /// }
    ///
    /// // The `Keys` iterator produces keys in arbitrary order, so the
    /// // keys must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, ["a", "b", "c"]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn keys(&self) -> Keys<'_, K> {
        Keys::new(self.full_keys())
    }

    /// Creates a consuming iterator visiting all the keys in arbitrary order.
    /// The map cannot be used after calling this.
    /// The iterator element type is `K`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// let mut vec: Vec<&str> = map.into_keys().collect();
    ///
    /// // The `IntoKeys` iterator produces keys in arbitrary order, so the
    /// // keys must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, ["a", "b", "c"]);
    /// ```
    pub fn into_keys(self) -> IntoKeys<K> {
        IntoKeys::new(self.table.into_iter())
    }

    /// An iterator over indices in arbitrary order. The iterator element type is `usize`.
    pub fn indices(&self) -> Indices<'_, K> {
        Indices::new(self.table.iter())
    }

    /// An iterator visiting all values in arbitrary order. The iterator element type is `&'a V`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    /// assert_eq!(map.len(), 3);
    /// let mut vec: Vec<i32> = Vec::new();
    ///
    /// for val in map.values() {
    ///     println!("{}", val);
    ///     vec.push(*val);
    /// }
    ///
    /// // The `Values` iterator produces values in arbitrary order, so the
    /// // values must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [1, 2, 3]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn values(&self) -> Values<'_, K, V> {
        Values::new(self.iter_full())
    }

    /// An iterator visiting all values mutably in arbitrary order. The iterator element type is `&'a mut V`.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    ///
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// for val in map.values_mut() {
    ///     *val = *val + 10;
    /// }
    ///
    /// assert_eq!(map.len(), 3);
    /// let mut vec: Vec<i32> = Vec::new();
    ///
    /// for val in map.values() {
    ///     println!("{}", val);
    ///     vec.push(*val);
    /// }
    ///
    /// // The `Values` iterator produces values in arbitrary order, so the
    /// // values must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [11, 12, 13]);
    ///
    /// assert_eq!(map.len(), 3);
    /// ```
    pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
        ValuesMut::new(self.iter_full_mut())
    }

    /// Creates a consuming iterator visiting all the values in arbitrary order.
    /// The map cannot be used after calling this.
    /// The iterator element type is `V`.
    ///
    /// # Examples
    ///
    /// ```
    /// use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// let mut vec: Vec<i32> = map.into_values().collect();
    ///
    /// // The `IntoValues` iterator produces values in arbitrary order, so
    /// // the values must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [1, 2, 3]);
    /// ```
    pub fn into_values(self) -> IntoValues<K, V> {
        IntoValues::new(self.into_iter())
    }

    /// Remove all entries in the map, while preserving its capacity.
    pub fn clear(&mut self) {
        self.table.clear();
        self.slab.clear();
    }

    /// Clears the map, returning all index-key-value triples as an iterator. Keeps the allocated memory for reuse.
    pub fn drain_full(&mut self) -> DrainFull<'_, K, V> {
        DrainFull::new(self.table.drain(), &mut self.slab)
    }

    /// Clears the map, returning all key-value pairs as an iterator. Keeps the allocated memory for reuse.
    pub fn drain(&mut self) -> Drain<'_, K, V> {
        Drain::new(self.drain_full())
    }

    /// Retains only the elements specified by the predicate. Keeps the
    /// allocated memory for reuse.
    ///
    /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)` returns `false`.
    /// The elements are visited in unsorted (and unspecified) order.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut map: HashSlabMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
    /// assert_eq!(map.len(), 8);
    ///
    /// map.retain(|&k, _| dbg!(k) % 2 == 0);
    ///
    /// // We can see, that the number of elements inside map is changed.
    /// assert_eq!(map.len(), 4);
    ///
    /// let mut vec: Vec<(i32, i32)> = map.iter().map(|(&k, &v)| (k, v)).collect();
    /// vec.sort_unstable();
    /// assert_eq!(vec, [(0, 0), (2, 20), (4, 40), (6, 60)]);
    /// ```
    pub fn retain<F>(&mut self, mut f: F)
    where
        F: FnMut(&K, &mut V) -> bool,
    {
        self.table.retain(|KeyData { key, index }| {
            let value = &mut self.slab[*index].value;
            if f(key, value) {
                true
            } else {
                self.slab.remove(*index);
                false
            }
        })
    }

    /// Get a key-value pair by index
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut map = HashSlabMap::new();
    /// map.insert(1, "a");
    /// assert_eq!(map.get_index(0), Some((&1, &"a")));
    /// assert_eq!(map.get_index(1), None);
    /// ```
    pub fn get_index(&self, index: usize) -> Option<(&K, &V)> {
        let ValueData { value, hash } = self.slab.get(index)?;
        self.table
            .find(*hash, |e| e.index == index)
            .map(|KeyData { key, .. }| (key, value))
    }

    /// Get a value by index.
    pub fn get_index_value(&self, index: usize) -> Option<&V> {
        self.slab.get(index).map(|ValueData { value, .. }| value)
    }

    /// Returns the index of the next vacant entry.
    ///
    /// This function returns the index of the vacant entry which  will be used
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::*;
    /// let mut map = HashSlabMap::new();
    /// assert_eq!(map.vacant_index(), 0);
    ///
    /// map.insert(0, ());
    /// assert_eq!(map.vacant_index(), 1);
    ///
    /// map.insert(1, ());
    /// map.remove(&0);
    /// assert_eq!(map.vacant_index(), 0);
    /// ```
    pub fn vacant_index(&self) -> usize {
        self.slab.vacant_key()
    }
}

impl<K, V, S> HashSlabMap<K, V, S>
where
    K: Hash + Eq,
    S: BuildHasher,
{
    /// Reserve capacity for `additional` more key-value pairs.
    pub fn reserve(&mut self, additional: usize) {
        self.table.reserve(additional, make_hasher(&self.builder));
        self.slab.reserve(additional);
    }

    /// Try to reserve capacity for `additional` more key-value pairs.
    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
        self.table
            .try_reserve(additional, make_hasher(&self.builder))?;
        let capacity = self.slab.capacity();
        if (capacity + additional) <= isize::MAX as usize {
            self.slab.reserve(additional);
            Ok(())
        } else {
            Err(TryReserveError::Slab {
                capacity,
                additional,
            })
        }
    }

    /// Shrink the capacity of the map as much as possible.
    pub fn shrink_to_fit(&mut self) {
        self.table.shrink_to_fit(make_hasher(&self.builder));
        self.slab.shrink_to_fit();
    }

    /// 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.
    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.
    pub fn insert_full(&mut self, key: K, value: V) -> (usize, Option<V>) {
        let hash = self.builder.hash_one(&key);
        match self
            .table
            .entry(hash, |e| e.key == key, make_hasher(&self.builder))
        {
            hash_table::Entry::Occupied(entry) => {
                let i = entry.get().index;
                (i, Some(mem::replace(&mut self.slab[i].value, value)))
            }
            hash_table::Entry::Vacant(entry) => {
                let index = self.slab.insert(ValueData::new(value, hash));
                entry.insert(KeyData::new(key, index));
                debug_assert_eq!(self.table.len(), self.slab.len());
                (index, None)
            }
        }
    }

    /// Return item index, key and value
    pub fn get_full<Q>(&self, key: &Q) -> Option<(usize, &K, &V)>
    where
        Q: Hash + Equivalent<K> + ?Sized,
    {
        self.get_key_index(key)
            .map(|(key, index)| (index, key, &self.slab[index].value))
    }

    /// Return references to the key-value pair stored for `key`, if it is present, else `None`.
    pub fn get_key_value<Q>(&self, key: &Q) -> Option<(&K, &V)>
    where
        Q: Hash + Equivalent<K> + ?Sized,
    {
        self.get_full(key).map(|(_, key, data)| (key, data))
    }

    /// Returns a reference to the value corresponding to the key.
    ///
    /// The key may be any borrowed form of the map's key type, but
    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
    /// the key type.
    ///
    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
    ///
    /// # Examples
    ///
    /// ```
    /// use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert(1, "a");
    /// assert_eq!(map.get(&1), Some(&"a"));
    /// assert_eq!(map.get(&2), None);
    /// ```
    pub fn get<Q>(&self, key: &Q) -> Option<&V>
    where
        Q: Hash + Equivalent<K> + ?Sized,
    {
        self.get_full(key).map(|(_, _, data)| data)
    }

    /// Return item index, if it exists in the map
    pub fn get_index_of<Q>(&self, key: &Q) -> Option<usize>
    where
        Q: Hash + Equivalent<K> + ?Sized,
    {
        self.get_key_index(key).map(|(_, index)| index)
    }

    /// Returns the index-key-value triple corresponding to the supplied key, with a mutable reference to value.
    pub fn get_full_mut<Q>(&mut self, key: &Q) -> Option<(usize, &K, &mut V)>
    where
        Q: ?Sized + Hash + Equivalent<K>,
    {
        if self.table.is_empty() {
            None
        } else {
            let hash = self.builder.hash_one(key);
            self.table
                .find(hash, |e| key.equivalent(&e.key))
                .map(|KeyData { index, key, .. }| (*index, key, &mut self.slab[*index].value))
        }
    }

    /// Returns a mutable reference to the value corresponding to the key.
    ///
    /// The key may be any borrowed form of the map's key type, but
    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
    /// the key type.
    ///
    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
    ///
    /// # Examples
    ///
    /// ```
    /// use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert(1, "a");
    /// if let Some(x) = map.get_mut(&1) {
    ///     *x = "b";
    /// }
    /// assert_eq!(map[&1], "b");
    ///
    /// assert_eq!(map.get_mut(&2), None);
    /// ```
    pub fn get_mut<Q>(&mut self, key: &Q) -> Option<&mut V>
    where
        Q: ?Sized + Hash + Equivalent<K>,
    {
        self.get_full_mut(key).map(|(_, _, value)| value)
    }

    /// Returns key reference and mutable reference to the value corresponding to the index.
    ///
    /// ```
    /// use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert(1, "a");
    /// if let Some((k, v)) = map.get_index_mut(0) {
    ///     *v = "b";
    /// }
    /// assert_eq!(map[&1], "b");
    ///
    /// assert_eq!(map.get_index_mut(1), None);
    /// ```
    pub fn get_index_mut(&mut self, index: usize) -> Option<(&K, &mut V)> {
        let ValueData { value, hash } = self.slab.get_mut(index)?;
        self.table
            .find(*hash, |e| e.index == index)
            .map(|KeyData { key, .. }| (key, value))
    }

    /// Remove the key-value pair equivalent to `key` and return its value.
    pub fn remove<Q>(&mut self, key: &Q) -> Option<V>
    where
        Q: ?Sized + Hash + Equivalent<K>,
    {
        self.remove_entry(key).map(|(_, v)| v)
    }

    /// Remove and return the key-value pair equivalent to `key`.
    pub fn remove_entry<Q>(&mut self, key: &Q) -> Option<(K, V)>
    where
        Q: ?Sized + Hash + Equivalent<K>,
    {
        self.remove_full(key).map(|(_, k, v)| (k, v))
    }

    /// Remove the key-value pair equivalent to key and return it and the index it had.
    pub fn remove_full<Q>(&mut self, key: &Q) -> Option<(usize, K, V)>
    where
        Q: ?Sized + Hash + Equivalent<K>,
    {
        let hash = self.builder.hash_one(key);
        self.table
            .find_entry(hash, |e| key.equivalent(&e.key))
            .ok()
            .map(|entry| {
                let (KeyData { key, index, .. }, _) = entry.remove();
                let ValueData { value, .. } = self.slab.remove(index);
                (index, key, value)
            })
    }

    /// Remove the key-value pair by index
    pub fn remove_index(&mut self, index: usize) -> Option<(K, V)> {
        let ValueData { value, hash } = self.slab.try_remove(index)?;
        self.table
            .find_entry(hash, |e| e.index == index)
            .ok()
            .map(|entry| {
                let (KeyData { key, .. }, _) = entry.remove();
                (key, value)
            })
    }

    /// Gets the given key's corresponding entry in the map for in-place manipulation.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut letters = HashSlabMap::new();
    ///
    /// for ch in "a short treatise on fungi".chars() {
    ///     let counter = letters.entry(ch).or_insert(0);
    ///     *counter += 1;
    /// }
    ///
    /// assert_eq!(letters[&'s'], 2);
    /// assert_eq!(letters[&'t'], 3);
    /// assert_eq!(letters[&'u'], 1);
    /// assert_eq!(letters.get(&'y'), None);
    /// ```
    pub fn entry(&mut self, key: K) -> Entry<'_, K, V> {
        // let key_entry = EntryBuilder::new(key, self.map.hasher()).key_entry(self.slab.vacant_key());
        // match self.table.entry(key) {
        //     hash_table::Entry::Occupied(occupied_entry) => {
        //         Entry::Occupied(OccupiedEntry::new(occupied_entry, &mut self.slab))
        //     }
        //     hash_table::Entry::Vacant(vacant_entry) => {
        //         Entry::Vacant(VacantEntry::new(vacant_entry, &mut self.slab))
        //     }
        // }
        let hash = self.builder.hash_one(&key);
        match self
            .table
            .entry(hash, |e| e.key == key, make_hasher(&self.builder))
        {
            hash_table::Entry::Occupied(occupied_entry) => {
                Entry::Occupied(OccupiedEntry::new(occupied_entry, &mut self.slab))
            }
            hash_table::Entry::Vacant(vacant_entry) => {
                Entry::Vacant(VacantEntry::new(vacant_entry, &mut self.slab, key, hash))
            }
        }
    }

    /// Returns `true` if the map contains a value for the specified key.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut map = HashSlabMap::new();
    /// map.insert(1, "a");
    /// assert_eq!(map.contains_key(&1), true);
    /// assert_eq!(map.contains_key(&2), false);
    /// ```
    pub fn contains_key<Q>(&self, key: &Q) -> bool
    where
        Q: Hash + Equivalent<K> + ?Sized,
    {
        let hash = self.builder.hash_one(key);
        self.table.find(hash, |e| key.equivalent(&e.key)).is_some()
    }

    /// Return `true` if a value is associated with the given key.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// let mut map = HashSlabMap::new();
    ///
    /// let idx = map.insert_full("hello", ()).0;
    /// assert!(map.contains_index(idx));
    ///
    /// map.remove_index(idx);
    ///
    /// assert!(!map.contains_index(idx));
    /// ```
    pub fn contains_index(&self, index: usize) -> bool {
        self.slab.contains(index)
    }

    /// Moves all key-value pairs from `other` into `self`, leaving `other` empty.
    ///
    /// This is equivalent to calling [`insert`][Self::insert] for each
    /// key-value pair from `other` in order, which means that for keys that
    /// already exist in `self`, their value is updated in the current position.
    ///
    /// # Examples
    ///
    /// ```
    /// # use hashslab::HashSlabMap;
    /// // Note: Key (3) is present in both maps.
    /// let mut a = HashSlabMap::from([(3, "c"), (2, "b"), (1, "a")]);
    /// let mut b = HashSlabMap::from([(3, "d"), (4, "e"), (5, "f")]);
    /// let old_capacity = b.capacity();
    ///
    /// a.append(&mut b);
    ///
    /// assert_eq!(a.len(), 5);
    /// assert_eq!(b.len(), 0);
    /// assert_eq!(b.capacity(), old_capacity);
    ///
    /// let mut keys: Vec<_> = a.keys().cloned().collect();
    /// keys.sort();
    /// assert_eq!(keys, vec![1, 2, 3, 4, 5]);
    ///
    /// // "c" was overwritten.
    /// assert_eq!(a[&3], "d");
    /// ```
    pub fn append<S2>(&mut self, other: &mut HashSlabMap<K, V, S2>) {
        self.extend(other.drain());
    }
}

// Private methods
impl<K, V, S> HashSlabMap<K, V, S> {
    fn get_key_index<Q>(&self, key: &Q) -> Option<(&K, usize)>
    where
        Q: Hash + Equivalent<K> + ?Sized,
        S: BuildHasher,
    {
        if self.table.is_empty() {
            None
        } else {
            let hash = self.builder.hash_one(key);
            self.table
                .find(hash, |e| key.equivalent(&e.key))
                .map(|KeyData { index, key, .. }| (key, *index))
        }
    }
}

// https://github.com/rust-lang/rust/issues/26925
impl<K: Clone, V: Clone, S: Clone> Clone for HashSlabMap<K, V, S> {
    fn clone(&self) -> Self {
        Self {
            table: self.table.clone(),
            slab: self.slab.clone(),
            builder: self.builder.clone(),
        }
    }
}

impl<K, V> fmt::Debug for HashSlabMap<K, V>
where
    K: fmt::Debug,
    V: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_map()
            .entries(self.iter_full().map(|(i, k, v)| (i, (k, v))))
            .finish()
    }
}

impl<K, V, S> Default for HashSlabMap<K, V, S>
where
    S: Default,
{
    fn default() -> Self {
        Self::with_capacity_and_hasher(0, S::default())
    }
}

/// Access [`HashSlabMap`] values corresponding to a key.
///
/// # Examples
///
/// ```
/// use hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::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 hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::new();
/// map.insert("foo", 1);
/// println!("{:?}", map["bar"]); // panics!
/// ```
impl<K, V, Q: ?Sized, S> Index<&Q> for HashSlabMap<K, V, S>
where
    K: Hash + Eq,
    Q: Hash + Equivalent<K>,
    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("HashSlabMap: key not found")
    }
}

/// Access [`HashSlabMap`] values at indexed positions.
///
/// # Examples
///
/// ```
/// use hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::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");
/// ```
///
/// ```should_panic
/// use hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::new();
/// map.insert("foo", 1);
/// println!("{:?}", map[10]); // panics!
/// ```
impl<K, V, S> Index<usize> for HashSlabMap<K, V, S>
where
    K: Hash + Eq,
    S: BuildHasher,
{
    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("HashSlabMap: index out of bounds")
            .1
    }
}

/// Access [`HashSlabMap`] 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 hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::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 hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::new();
/// map.insert("foo", 1);
/// map["bar"] = 1; // panics!
/// ```
impl<K, V, Q: ?Sized, S> IndexMut<&Q> for HashSlabMap<K, V, S>
where
    K: Hash + Eq,
    Q: Hash + Equivalent<K>,
    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("HashSlabMap: key not found")
    }
}

/// Access [`HashSlabMap`] 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()`][HashSlabMap::insert].
///
/// # Examples
///
/// ```
/// use hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::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 hashslab::HashSlabMap;
///
/// let mut map = HashSlabMap::new();
/// map.insert("foo", 1);
/// map[10] = 1; // panics!
/// ```
impl<K, V, S> IndexMut<usize> for HashSlabMap<K, V, S>
where
    K: Hash + Eq,
    S: BuildHasher,
{
    /// 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("HashSlabMap: index out of bounds")
            .1
    }
}

impl<K, V, S> Extend<(K, V)> for HashSlabMap<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`][HashSlabMap::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.
    ///
    /// # Examples
    ///
    /// ```
    /// use hashslab::HashSlabMap;
    ///
    /// let mut map = HashSlabMap::new();
    /// map.insert(1, 100);
    ///
    /// let some_iter = [(1, 1), (2, 2)].into_iter();
    /// map.extend(some_iter);
    /// // Replace values with existing keys with new values returned from the iterator.
    /// // So that the map.get(&1) doesn't return Some(&100).
    /// assert_eq!(map.get(&1), Some(&1));
    ///
    /// let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
    /// map.extend(some_vec);
    ///
    /// let some_arr = [(5, 5), (6, 6)];
    /// map.extend(some_arr);
    /// let old_map_len = map.len();
    ///
    /// // You can also extend from another HashSlabMap
    /// let mut new_map = HashSlabMap::new();
    /// new_map.extend(map);
    /// assert_eq!(new_map.len(), old_map_len);
    ///
    /// let mut vec: Vec<_> = new_map.into_iter().collect();
    /// // The `IntoIter` iterator produces items in arbitrary order, so the
    /// // items must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
    /// ```
    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 HashSlabMap<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)));
    }
}

/// Inserts all new key-values from the iterator and replaces values with existing
/// keys with new values returned from the iterator.
impl<'a, K, V, S> Extend<&'a (K, V)> for HashSlabMap<K, V, S>
where
    K: Eq + Hash + Copy,
    V: Copy,
    S: BuildHasher,
{
    /// Inserts all new key-values from the iterator to existing `HashSlabMap<K, V, S, A>`.
    /// Replace values with existing keys with new values returned from the iterator.
    /// The keys and values must implement [`Copy`] trait.
    ///
    /// [`Copy`]: https://doc.rust-lang.org/core/marker/trait.Copy.html
    ///
    /// # Examples
    ///
    /// ```
    /// use hashslab::HashSlabMap;
    /// let mut map = HashSlabMap::new();
    /// map.insert(1, 100);
    ///
    /// let arr = [(1, 1), (2, 2)];
    /// let some_iter = arr.iter();
    /// map.extend(some_iter);
    /// // Replace values with existing keys with new values returned from the iterator.
    /// // So that the map.get(&1) doesn't return Some(&100).
    /// assert_eq!(map.get(&1), Some(&1));
    ///
    /// let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
    /// map.extend(&some_vec);
    ///
    /// let some_arr = [(5, 5), (6, 6)];
    /// map.extend(&some_arr);
    ///
    /// let mut vec: Vec<_> = map.into_iter().collect();
    /// // The `IntoIter` iterator produces items in arbitrary order, so the
    /// // items must be sorted to test them against a sorted array.
    /// vec.sort_unstable();
    /// assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);
    /// ```
    fn extend<T: IntoIterator<Item = &'a (K, V)>>(&mut self, iter: T) {
        self.extend(iter.into_iter().map(|&(key, value)| (key, value)));
    }
}

impl<K, V, S> FromIterator<(K, V)> for HashSlabMap<K, V, S>
where
    K: Hash + Eq,
    S: BuildHasher + Default,
{
    /// Create an `HashSlabMap` from the sequence of key-value pairs in the
    /// iterable.
    ///
    /// `from_iter` uses the same logic as `extend`. See
    /// [`extend`][HashSlabMap::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, S::default());
        map.extend(iter);
        map
    }
}

impl<K, V, const N: usize> From<[(K, V); N]> for HashSlabMap<K, V, RandomState>
where
    K: Hash + Eq,
{
    /// # Examples
    ///
    /// ```
    /// use hashslab::HashSlabMap;
    ///
    /// let map1 = HashSlabMap::from([(1, 2), (3, 4)]);
    /// let map2: HashSlabMap<_, _> = [(1, 2), (3, 4)].into();
    /// assert_eq!(map1, map2);
    /// ```
    fn from(arr: [(K, V); N]) -> Self {
        Self::from_iter(arr)
    }
}

impl<K, V1, S1, V2, S2> PartialEq<HashSlabMap<K, V2, S2>> for HashSlabMap<K, V1, S1>
where
    K: Hash + Eq,
    V1: PartialEq<V2>,
    S1: BuildHasher,
    S2: BuildHasher,
{
    fn eq(&self, other: &HashSlabMap<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 HashSlabMap<K, V, S>
where
    K: Eq + Hash,
    V: Eq,
    S: BuildHasher,
{
}

#[inline]
pub(crate) fn make_hasher<K, S>(hash_builder: &S) -> impl Fn(&KeyData<K>) -> u64 + '_
where
    K: Hash,
    S: BuildHasher,
{
    move |val| hash_builder.hash_one(&val.key)
}