map.rs

use crate::raw::{Bucket, RawIntoIter, RawIter, RawTable};
use crate::TryReserveError;
use core::borrow::Borrow;
use core::fmt::{self, Debug};
use core::hash::{BuildHasher, Hash, Hasher};
use core::iter::{FromIterator, FusedIterator};
use core::marker::PhantomData;
use core::mem;
use core::ops::Index;

#[doc(inline)]
pub use hashbrown::hash_map::DefaultHashBuilder;

/// A `HashMap` variant that spreads resize load across inserts.
///
/// See the [crate-level documentation] for details.
///
/// [crate-level documentation]: index.html
///
/// The default hashing algorithm is currently [`AHash`], though this is
/// subject to change at any point in the future. This hash function is very
/// fast for all types of keys, but this algorithm will typically *not* protect
/// against attacks such as HashDoS.
///
/// The hashing algorithm can be replaced on a per-`HashMap` basis using the
/// [`default`], [`with_hasher`], and [`with_capacity_and_hasher`] methods. Many
/// alternative algorithms are available on crates.io, such as the [`fnv`] crate.
///
/// It is required that the keys implement the [`Eq`] and [`Hash`] traits, although
/// this can frequently be achieved by using `#[derive(PartialEq, Eq, Hash)]`.
/// If you implement these yourself, it is important that the following
/// property holds:
///
/// ```text
/// k1 == k2 -> hash(k1) == hash(k2)
/// ```
///
/// In other words, if two keys are equal, their hashes must be equal.
///
/// It is a logic error for a key to be modified in such a way that the key's
/// hash, as determined by the [`Hash`] trait, or its equality, as determined by
/// the [`Eq`] trait, changes while it is in the map. This is normally only
/// possible through [`Cell`], [`RefCell`], global state, I/O, or unsafe code.
///
/// It is also a logic error for the [`Hash`] implementation of a key to panic.
/// This is generally only possible if the trait is implemented manually. If a
/// panic does occur then the contents of the `HashMap` may become corrupted and
/// some items may be dropped from the table.
///
/// # Examples
///
/// ```
/// use griddle::HashMap;
///
/// // Type inference lets us omit an explicit type signature (which
/// // would be `HashMap<String, String>` in this example).
/// let mut book_reviews = HashMap::new();
///
/// // Review some books.
/// book_reviews.insert(
///     "Adventures of Huckleberry Finn".to_string(),
///     "My favorite book.".to_string(),
/// );
/// book_reviews.insert(
///     "Grimms' Fairy Tales".to_string(),
///     "Masterpiece.".to_string(),
/// );
/// book_reviews.insert(
///     "Pride and Prejudice".to_string(),
///     "Very enjoyable.".to_string(),
/// );
/// book_reviews.insert(
///     "The Adventures of Sherlock Holmes".to_string(),
///     "Eye lyked it alot.".to_string(),
/// );
///
/// // Check for a specific one.
/// // When collections store owned values (String), they can still be
/// // queried using references (&str).
/// if !book_reviews.contains_key("Les Misérables") {
///     println!("We've got {} reviews, but Les Misérables ain't one.",
///              book_reviews.len());
/// }
///
/// // oops, this review has a lot of spelling mistakes, let's delete it.
/// book_reviews.remove("The Adventures of Sherlock Holmes");
///
/// // Look up the values associated with some keys.
/// let to_find = ["Pride and Prejudice", "Alice's Adventure in Wonderland"];
/// for &book in &to_find {
///     match book_reviews.get(book) {
///         Some(review) => println!("{}: {}", book, review),
///         None => println!("{} is unreviewed.", book)
///     }
/// }
///
/// // Look up the value for a key (will panic if the key is not found).
/// println!("Review for Jane: {}", book_reviews["Pride and Prejudice"]);
///
/// // Iterate over everything.
/// for (book, review) in &book_reviews {
///     println!("{}: \"{}\"", book, review);
/// }
/// ```
///
/// `HashMap` also implements an [`Entry API`](#method.entry), which allows
/// for more complex methods of getting, setting, updating and removing keys and
/// their values:
///
/// ```
/// use griddle::HashMap;
///
/// // type inference lets us omit an explicit type signature (which
/// // would be `HashMap<&str, u8>` in this example).
/// let mut player_stats = HashMap::new();
///
/// fn random_stat_buff() -> u8 {
///     // could actually return some random value here - let's just return
///     // some fixed value for now
///     42
/// }
///
/// // insert a key only if it doesn't already exist
/// player_stats.entry("health").or_insert(100);
///
/// // insert a key using a function that provides a new value only if it
/// // doesn't already exist
/// player_stats.entry("defence").or_insert_with(random_stat_buff);
///
/// // update a key, guarding against the key possibly not being set
/// let stat = player_stats.entry("attack").or_insert(100);
/// *stat += random_stat_buff();
/// ```
///
/// The easiest way to use `HashMap` with a custom key type is to derive [`Eq`] and [`Hash`].
/// We must also derive [`PartialEq`].
///
/// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
/// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
/// [`PartialEq`]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html
/// [`RefCell`]: https://doc.rust-lang.org/std/cell/struct.RefCell.html
/// [`Cell`]: https://doc.rust-lang.org/std/cell/struct.Cell.html
/// [`default`]: #method.default
/// [`with_hasher`]: #method.with_hasher
/// [`with_capacity_and_hasher`]: #method.with_capacity_and_hasher
/// [`fnv`]: https://crates.io/crates/fnv
/// [`AHash`]: https://crates.io/crates/ahash
///
/// ```
/// use griddle::HashMap;
///
/// #[derive(Hash, Eq, PartialEq, Debug)]
/// struct Viking {
///     name: String,
///     country: String,
/// }
///
/// impl Viking {
///     /// Creates a new Viking.
///     fn new(name: &str, country: &str) -> Viking {
///         Viking { name: name.to_string(), country: country.to_string() }
///     }
/// }
///
/// // Use a HashMap to store the vikings' health points.
/// let mut vikings = HashMap::new();
///
/// vikings.insert(Viking::new("Einar", "Norway"), 25);
/// vikings.insert(Viking::new("Olaf", "Denmark"), 24);
/// vikings.insert(Viking::new("Harald", "Iceland"), 12);
///
/// // Use derived implementation to print the status of the vikings.
/// for (viking, health) in &vikings {
///     println!("{:?} has {} hp", viking, health);
/// }
/// ```
///
/// A `HashMap` with fixed list of elements can be initialized from an array:
///
/// ```
/// use griddle::HashMap;
///
/// let timber_resources: HashMap<&str, i32> = [("Norway", 100), ("Denmark", 50), ("Iceland", 10)]
///     .iter().cloned().collect();
/// // use the values stored in map
/// ```
pub struct HashMap<K, V, S = DefaultHashBuilder> {
    pub(crate) hash_builder: S,
    pub(crate) table: RawTable<(K, V)>,
}

impl<K: Clone, V: Clone, S: Clone> Clone for HashMap<K, V, S> {
    fn clone(&self) -> Self {
        HashMap {
            hash_builder: self.hash_builder.clone(),
            table: self.table.clone(),
        }
    }

    fn clone_from(&mut self, source: &Self) {
        self.table.clone_from(&source.table);

        // Update hash_builder only if we successfully cloned all elements.
        self.hash_builder.clone_from(&source.hash_builder);
    }
}

#[cfg_attr(feature = "inline-more", inline)]
pub(crate) fn make_hash<K: Hash + ?Sized>(hash_builder: &impl BuildHasher, val: &K) -> u64 {
    let mut state = hash_builder.build_hasher();
    val.hash(&mut state);
    state.finish()
}

#[cfg(feature = "ahash")]
impl<K, V> HashMap<K, V, DefaultHashBuilder> {
    /// Creates an empty `HashMap`.
    ///
    /// The hash map is initially created with a capacity of 0, so it will not allocate until it
    /// is first inserted into.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// let mut map: HashMap<&str, i32> = HashMap::new();
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn new() -> Self {
        Self::default()
    }

    /// Creates an empty `HashMap` with the specified capacity.
    ///
    /// The hash map will be able to hold at least `capacity` elements without
    /// reallocating. If `capacity` is 0, the hash map will not allocate.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn with_capacity(capacity: usize) -> Self {
        Self::with_capacity_and_hasher(capacity, DefaultHashBuilder::default())
    }
}

impl<K, V, S> HashMap<K, V, S> {
    /// Creates an empty `HashMap` which will use the given hash builder to hash
    /// keys.
    ///
    /// The created map has the default initial capacity.
    ///
    /// Warning: `hash_builder` is normally randomly generated, and
    /// is designed to allow HashMaps to be resistant to attacks that
    /// cause many collisions and very poor performance. Setting it
    /// manually using this function can expose a DoS attack vector.
    ///
    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
    /// the HashMap to be useful, see its documentation for details.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::DefaultHashBuilder;
    ///
    /// let s = DefaultHashBuilder::default();
    /// let mut map = HashMap::with_hasher(s);
    /// map.insert(1, 2);
    /// ```
    ///
    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn with_hasher(hash_builder: S) -> Self {
        Self {
            hash_builder,
            table: RawTable::new(),
        }
    }

    /// Creates an empty `HashMap` with the specified capacity, using `hash_builder`
    /// to hash the keys.
    ///
    /// The hash map will be able to hold at least `capacity` elements without
    /// reallocating. If `capacity` is 0, the hash map will not allocate.
    ///
    /// Warning: `hash_builder` is normally randomly generated, and
    /// is designed to allow HashMaps to be resistant to attacks that
    /// cause many collisions and very poor performance. Setting it
    /// manually using this function can expose a DoS attack vector.
    ///
    /// The `hash_builder` passed should implement the [`BuildHasher`] trait for
    /// the HashMap to be useful, see its documentation for details.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::DefaultHashBuilder;
    ///
    /// let s = DefaultHashBuilder::default();
    /// let mut map = HashMap::with_capacity_and_hasher(10, s);
    /// map.insert(1, 2);
    /// ```
    ///
    /// [`BuildHasher`]: ../../std/hash/trait.BuildHasher.html
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self {
        Self {
            hash_builder,
            table: RawTable::with_capacity(capacity),
        }
    }

    /// Returns a reference to the map's [`BuildHasher`].
    ///
    /// [`BuildHasher`]: https://doc.rust-lang.org/std/hash/trait.BuildHasher.html
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::DefaultHashBuilder;
    ///
    /// let hasher = DefaultHashBuilder::default();
    /// let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
    /// let hasher: &DefaultHashBuilder = map.hasher();
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn hasher(&self) -> &S {
        &self.hash_builder
    }

    /// Returns the number of elements the map can hold without reallocating.
    ///
    /// This number is a lower bound; the `HashMap<K, V>` might be able to hold
    /// more, but is guaranteed to be able to hold at least this many.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// let map: HashMap<i32, i32> = HashMap::with_capacity(100);
    /// assert!(map.capacity() >= 100);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn capacity(&self) -> usize {
        self.table.capacity()
    }

    /// An iterator visiting all keys in arbitrary order.
    /// The iterator element type is `&'a K`.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// for key in map.keys() {
    ///     println!("{}", key);
    /// }
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn keys(&self) -> Keys<'_, K, V> {
        Keys { inner: self.iter() }
    }

    /// An iterator visiting all values in arbitrary order.
    /// The iterator element type is `&'a V`.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// for val in map.values() {
    ///     println!("{}", val);
    /// }
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn values(&self) -> Values<'_, K, V> {
        Values { inner: self.iter() }
    }

    /// An iterator visiting all values mutably in arbitrary order.
    /// The iterator element type is `&'a mut V`.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    ///
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// for val in map.values_mut() {
    ///     *val = *val + 10;
    /// }
    ///
    /// for val in map.values() {
    ///     println!("{}", val);
    /// }
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn values_mut(&mut self) -> ValuesMut<'_, K, V> {
        ValuesMut {
            inner: self.iter_mut(),
        }
    }

    /// An iterator visiting all key-value pairs in arbitrary order.
    /// The iterator element type is `(&'a K, &'a V)`.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// for (key, val) in map.iter() {
    ///     println!("key: {} val: {}", key, val);
    /// }
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn iter(&self) -> Iter<'_, K, V> {
        // Here we tie the lifetime of self to the iter.
        unsafe {
            Iter {
                inner: self.table.iter(),
                marker: PhantomData,
            }
        }
    }

    /// An iterator visiting all key-value pairs in arbitrary order,
    /// with mutable references to the values.
    /// The iterator element type is `(&'a K, &'a mut V)`.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// // Update all values
    /// for (_, val) in map.iter_mut() {
    ///     *val *= 2;
    /// }
    ///
    /// for (key, val) in &map {
    ///     println!("key: {} val: {}", key, val);
    /// }
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn iter_mut(&mut self) -> IterMut<'_, K, V> {
        // Here we tie the lifetime of self to the iter.
        unsafe {
            IterMut {
                inner: self.table.iter(),
                marker: PhantomData,
            }
        }
    }

    #[cfg(test)]
    #[cfg_attr(feature = "inline-more", inline)]
    fn raw_capacity(&self) -> usize {
        self.table.buckets()
    }

    #[cfg(test)]
    fn is_split(&self) -> bool {
        self.table.is_split()
    }

    /// Returns the number of elements in the map.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut a = HashMap::new();
    /// assert_eq!(a.len(), 0);
    /// a.insert(1, "a");
    /// assert_eq!(a.len(), 1);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn len(&self) -> usize {
        self.table.len()
    }

    /// Returns `true` if the map contains no elements.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut a = HashMap::new();
    /// assert!(a.is_empty());
    /// a.insert(1, "a");
    /// assert!(!a.is_empty());
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Retains only the elements specified by the predicate.
    ///
    /// In other words, remove all pairs `(k, v)` such that `f(&k,&mut v)` returns `false`.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
    /// map.retain(|&k, _| k % 2 == 0);
    /// assert_eq!(map.len(), 4);
    /// ```
    pub fn retain<F>(&mut self, mut f: F)
    where
        F: FnMut(&K, &mut V) -> bool,
    {
        // Here we only use `iter` as a temporary, preventing use-after-free
        unsafe {
            for item in self.table.iter() {
                let &mut (ref key, ref mut value) = item.as_mut();
                if !f(key, value) {
                    // Erase the element from the table first since drop might panic.
                    // But read it before the erase in case erase invalidates the memory.
                    let v = item.read();
                    self.table.erase_no_drop(&item);
                    drop(v);
                }
            }
        }
    }

    /// Clears the map, removing all key-value pairs. Keeps the allocated memory
    /// for reuse.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut a = HashMap::new();
    /// a.insert(1, "a");
    /// a.clear();
    /// assert!(a.is_empty());
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn clear(&mut self) {
        self.table.clear();
    }
}

impl<K, V, S> HashMap<K, V, S>
where
    K: Eq + Hash,
    S: BuildHasher,
{
    /// Reserves capacity for at least `additional` more elements to be inserted
    /// in the `HashMap`. The collection may reserve more space to avoid
    /// frequent reallocations.
    ///
    /// While we try to make this incremental where possible,
    /// it may require all-at-once resizing.
    ///
    /// # Panics
    ///
    /// Panics if the new allocation size overflows [`usize`].
    ///
    /// [`usize`]: https://doc.rust-lang.org/std/primitive.usize.html
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// let mut map: HashMap<&str, i32> = HashMap::new();
    /// map.reserve(10);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn reserve(&mut self, additional: usize) {
        let hash_builder = &self.hash_builder;
        self.table
            .reserve(additional, |x| make_hash(hash_builder, &x.0));
    }

    /// Tries to reserve capacity for at least `additional` more elements to be inserted
    /// in the given `HashMap<K,V>`. The collection may reserve more space to avoid
    /// frequent reallocations.
    ///
    /// While we try to make this incremental where possible,
    /// it may require all-at-once resizing.
    ///
    /// # Errors
    ///
    /// If the capacity overflows, or the allocator reports a failure, then an error
    /// is returned.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// let mut map: HashMap<&str, isize> = HashMap::new();
    /// map.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError> {
        let hash_builder = &self.hash_builder;
        self.table
            .try_reserve(additional, |x| make_hash(hash_builder, &x.0))
    }

    /// Shrinks the capacity of the map as much as possible. It will drop
    /// down as much as possible while maintaining the internal rules
    /// and possibly leaving some space in accordance with the resize policy.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
    /// map.insert(1, 2);
    /// map.insert(3, 4);
    /// assert!(map.capacity() >= 100);
    /// map.shrink_to_fit();
    /// assert!(map.capacity() >= 2);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn shrink_to_fit(&mut self) {
        let hash_builder = &self.hash_builder;
        self.table.shrink_to(0, |x| make_hash(hash_builder, &x.0));
    }

    /// Shrinks the capacity of the map with a lower limit. It will drop
    /// down no lower than the supplied limit while maintaining the internal rules
    /// and possibly leaving some space in accordance with the resize policy.
    ///
    /// This function does nothing if the current capacity is smaller than the
    /// supplied minimum capacity.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<i32, i32> = HashMap::with_capacity(100);
    /// map.insert(1, 2);
    /// map.insert(3, 4);
    /// assert!(map.capacity() >= 100);
    /// map.shrink_to(10);
    /// assert!(map.capacity() >= 10);
    /// map.shrink_to(0);
    /// assert!(map.capacity() >= 2);
    /// map.shrink_to(10);
    /// assert!(map.capacity() >= 2);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn shrink_to(&mut self, min_capacity: usize) {
        let hash_builder = &self.hash_builder;
        self.table
            .shrink_to(min_capacity, |x| make_hash(hash_builder, &x.0));
    }

    /// Gets the given key's corresponding entry in the map for in-place manipulation.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut letters = HashMap::new();
    ///
    /// for ch in "a short treatise on fungi".chars() {
    ///     let counter = letters.entry(ch).or_insert(0);
    ///     *counter += 1;
    /// }
    ///
    /// assert_eq!(letters[&'s'], 2);
    /// assert_eq!(letters[&'t'], 3);
    /// assert_eq!(letters[&'u'], 1);
    /// assert_eq!(letters.get(&'y'), None);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn entry(&mut self, key: K) -> Entry<'_, K, V, S> {
        let hash = make_hash(&self.hash_builder, &key);
        if let Some(elem) = self.table.find(hash, |q| q.0.eq(&key)) {
            Entry::Occupied(OccupiedEntry {
                key: Some(key),
                elem,
                table: self,
            })
        } else {
            Entry::Vacant(VacantEntry {
                hash,
                key,
                table: self,
            })
        }
    }

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

    /// Returns the key-value pair corresponding to the supplied key.
    ///
    /// The supplied key may be any borrowed form of the map's key type, but
    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
    /// the key type.
    ///
    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert(1, "a");
    /// assert_eq!(map.get_key_value(&1), Some((&1, &"a")));
    /// assert_eq!(map.get_key_value(&2), None);
    /// ```
    #[inline]
    pub fn get_key_value<Q: ?Sized>(&self, k: &Q) -> Option<(&K, &V)>
    where
        K: Borrow<Q>,
        Q: Hash + Eq,
    {
        let hash = make_hash(&self.hash_builder, k);
        self.table
            .find(hash, |x| k.eq(x.0.borrow()))
            .map(|item| unsafe {
                let &(ref key, ref value) = item.as_ref();
                (key, value)
            })
    }

    /// Returns the key-value pair corresponding to the supplied key, with a mutable reference to value.
    ///
    /// The supplied key may be any borrowed form of the map's key type, but
    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
    /// the key type.
    ///
    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert(1, "a");
    /// let (k, v) = map.get_key_value_mut(&1).unwrap();
    /// assert_eq!(k, &1);
    /// assert_eq!(v, &mut "a");
    /// *v = "b";
    /// assert_eq!(map.get_key_value_mut(&1), Some((&1, &mut "b")));
    /// assert_eq!(map.get_key_value_mut(&2), None);
    /// ```
    #[inline]
    pub fn get_key_value_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<(&K, &mut V)>
    where
        K: Borrow<Q>,
        Q: Hash + Eq,
    {
        let hash = make_hash(&self.hash_builder, k);
        self.table
            .find(hash, |x| k.eq(x.0.borrow()))
            .map(|item| unsafe {
                let &mut (ref key, ref mut value) = item.as_mut();
                (key, value)
            })
    }

    /// Returns `true` if the map contains a value for the specified key.
    ///
    /// The key may be any borrowed form of the map's key type, but
    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
    /// the key type.
    ///
    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert(1, "a");
    /// assert_eq!(map.contains_key(&1), true);
    /// assert_eq!(map.contains_key(&2), false);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn contains_key<Q: ?Sized>(&self, k: &Q) -> bool
    where
        K: Borrow<Q>,
        Q: Hash + Eq,
    {
        self.get(k).is_some()
    }

    /// Returns a mutable reference to the value corresponding to the key.
    ///
    /// The key may be any borrowed form of the map's key type, but
    /// [`Hash`] and [`Eq`] on the borrowed form *must* match those for
    /// the key type.
    ///
    /// [`Eq`]: https://doc.rust-lang.org/std/cmp/trait.Eq.html
    /// [`Hash`]: https://doc.rust-lang.org/std/hash/trait.Hash.html
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert(1, "a");
    /// if let Some(x) = map.get_mut(&1) {
    ///     *x = "b";
    /// }
    /// assert_eq!(map[&1], "b");
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn get_mut<Q: ?Sized>(&mut self, k: &Q) -> Option<&mut V>
    where
        K: Borrow<Q>,
        Q: Hash + Eq,
    {
        let hash = make_hash(&self.hash_builder, k);
        self.table
            .find(hash, |x| k.eq(x.0.borrow()))
            .map(|item| unsafe { &mut item.as_mut().1 })
    }

    /// Inserts a key-value pair into the map.
    ///
    /// If the map did not have this key present, [`None`] is returned.
    ///
    /// If the map did have this key present, the value is updated, and the old
    /// value is returned. The key is not updated, though; this matters for
    /// types that can be `==` without being identical. See the [module-level
    /// documentation] for more.
    ///
    /// [`None`]: https://doc.rust-lang.org/std/option/enum.Option.html#variant.None
    /// [module-level documentation]: index.html#insert-and-complex-keys
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// assert_eq!(map.insert(37, "a"), None);
    /// assert_eq!(map.is_empty(), false);
    ///
    /// map.insert(37, "b");
    /// assert_eq!(map.insert(37, "c"), Some("b"));
    /// assert_eq!(map[&37], "c");
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn insert(&mut self, k: K, v: V) -> Option<V> {
        unsafe {
            let hash = make_hash(&self.hash_builder, &k);
            if let Some(item) = self.table.find(hash, |x| k.eq(&x.0)) {
                let v = Some(mem::replace(&mut item.as_mut().1, v));
                if item.will_move() {
                    debug_assert!(self.table.is_split());
                    let hash_builder = &self.hash_builder;
                    self.table.carry(|x| make_hash(hash_builder, &x.0));
                }
                v
            } else {
                let hash_builder = &self.hash_builder;
                self.table
                    .insert(hash, (k, v), |x| make_hash(hash_builder, &x.0));
                None
            }
        }
    }

    /// Removes a key from the map, returning the value at the key if the key
    /// was previously in the map.
    ///
    /// 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 griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert(1, "a");
    /// assert_eq!(map.remove(&1), Some("a"));
    /// assert_eq!(map.remove(&1), None);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn remove<Q: ?Sized>(&mut self, k: &Q) -> Option<V>
    where
        K: Borrow<Q>,
        Q: Hash + Eq,
    {
        self.remove_entry(k).map(|(_, v)| v)
    }

    /// Removes a key from the map, returning the stored key and value if the
    /// key was previously in the map.
    ///
    /// 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 griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert(1, "a");
    /// assert_eq!(map.remove_entry(&1), Some((1, "a")));
    /// assert_eq!(map.remove(&1), None);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn remove_entry<Q: ?Sized>(&mut self, k: &Q) -> Option<(K, V)>
    where
        K: Borrow<Q>,
        Q: Hash + Eq,
    {
        unsafe {
            let hash = make_hash(&self.hash_builder, &k);
            if let Some(item) = self.table.find(hash, |x| k.eq(x.0.borrow())) {
                // Read the item before the erase, in case erase reclaims memory.
                let v = item.read();
                self.table.erase_no_drop(&item);
                Some(v)
            } else {
                None
            }
        }
    }
}

impl<K, V, S> PartialEq for HashMap<K, V, S>
where
    K: Eq + Hash,
    V: PartialEq,
    S: BuildHasher,
{
    fn eq(&self, other: &Self) -> bool {
        if self.len() != other.len() {
            return false;
        }

        self.iter()
            .all(|(key, value)| other.get(key).map_or(false, |v| *value == *v))
    }
}

impl<K, V, S> Eq for HashMap<K, V, S>
where
    K: Eq + Hash,
    V: Eq,
    S: BuildHasher,
{
}

impl<K, V, S> Debug for HashMap<K, V, S>
where
    K: Debug,
    V: Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_map().entries(self.iter()).finish()
    }
}

impl<K, V, S> Default for HashMap<K, V, S>
where
    S: Default,
{
    /// Creates an empty `HashMap<K, V, S>`, with the `Default` value for the hasher.
    #[cfg_attr(feature = "inline-more", inline)]
    fn default() -> Self {
        Self::with_hasher(Default::default())
    }
}

impl<K, Q: ?Sized, V, S> Index<&Q> for HashMap<K, V, S>
where
    K: Eq + Hash + Borrow<Q>,
    Q: Eq + Hash,
    S: BuildHasher,
{
    type Output = V;

    /// Returns a reference to the value corresponding to the supplied key.
    ///
    /// # Panics
    ///
    /// Panics if the key is not present in the `HashMap`.
    #[cfg_attr(feature = "inline-more", inline)]
    fn index(&self, key: &Q) -> &V {
        self.get(key).expect("no entry found for key")
    }
}

/// An iterator over the entries of a `HashMap`.
///
/// This `struct` is created by the [`iter`] method on [`HashMap`]. See its
/// documentation for more.
///
/// [`iter`]: struct.HashMap.html#method.iter
/// [`HashMap`]: struct.HashMap.html
pub struct Iter<'a, K, V> {
    inner: RawIter<(K, V)>,
    marker: PhantomData<(&'a K, &'a V)>,
}

// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
impl<K, V> Clone for Iter<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn clone(&self) -> Self {
        Iter {
            inner: self.inner.clone(),
            marker: PhantomData,
        }
    }
}

impl<K: Debug, V: Debug> fmt::Debug for Iter<'_, K, V> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_list().entries(self.clone()).finish()
    }
}

/// A mutable iterator over the entries of a `HashMap`.
///
/// This `struct` is created by the [`iter_mut`] method on [`HashMap`]. See its
/// documentation for more.
///
/// [`iter_mut`]: struct.HashMap.html#method.iter_mut
/// [`HashMap`]: struct.HashMap.html
pub struct IterMut<'a, K, V> {
    inner: RawIter<(K, V)>,
    // To ensure invariance with respect to V
    marker: PhantomData<(&'a K, &'a mut V)>,
}

// We override the default Send impl which has K: Sync instead of K: Send. Both
// are correct, but this one is more general since it allows keys which
// implement Send but not Sync.
unsafe impl<K: Send, V: Send> Send for IterMut<'_, K, V> {}

impl<K, V> IterMut<'_, K, V> {
    /// Returns a iterator of references over the remaining items.
    #[cfg_attr(feature = "inline-more", inline)]
    pub(super) fn iter(&self) -> Iter<'_, K, V> {
        Iter {
            inner: self.inner.clone(),
            marker: PhantomData,
        }
    }
}

/// An owning iterator over the entries of a `HashMap`.
///
/// This `struct` is created by the [`into_iter`] method on [`HashMap`]
/// (provided by the `IntoIterator` trait). See its documentation for more.
///
/// [`into_iter`]: struct.HashMap.html#method.into_iter
/// [`HashMap`]: struct.HashMap.html
pub struct IntoIter<K, V> {
    inner: RawIntoIter<(K, V)>,
}

impl<K, V> IntoIter<K, V> {
    /// Returns a iterator of references over the remaining items.
    #[cfg_attr(feature = "inline-more", inline)]
    pub(super) fn iter(&self) -> Iter<'_, K, V> {
        Iter {
            inner: self.inner.iter(),
            marker: PhantomData,
        }
    }
}

/// An iterator over the keys of a `HashMap`.
///
/// This `struct` is created by the [`keys`] method on [`HashMap`]. See its
/// documentation for more.
///
/// [`keys`]: struct.HashMap.html#method.keys
/// [`HashMap`]: struct.HashMap.html
pub struct Keys<'a, K, V> {
    inner: Iter<'a, K, V>,
}

// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
impl<K, V> Clone for Keys<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn clone(&self) -> Self {
        Keys {
            inner: self.inner.clone(),
        }
    }
}

impl<K: Debug, V> fmt::Debug for Keys<'_, K, V> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_list().entries(self.clone()).finish()
    }
}

/// An iterator over the values of a `HashMap`.
///
/// This `struct` is created by the [`values`] method on [`HashMap`]. See its
/// documentation for more.
///
/// [`values`]: struct.HashMap.html#method.values
/// [`HashMap`]: struct.HashMap.html
pub struct Values<'a, K, V> {
    inner: Iter<'a, K, V>,
}

// FIXME(#26925) Remove in favor of `#[derive(Clone)]`
impl<K, V> Clone for Values<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn clone(&self) -> Self {
        Values {
            inner: self.inner.clone(),
        }
    }
}

impl<K, V: Debug> fmt::Debug for Values<'_, K, V> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_list().entries(self.clone()).finish()
    }
}

/// A mutable iterator over the values of a `HashMap`.
///
/// This `struct` is created by the [`values_mut`] method on [`HashMap`]. See its
/// documentation for more.
///
/// [`values_mut`]: struct.HashMap.html#method.values_mut
/// [`HashMap`]: struct.HashMap.html
pub struct ValuesMut<'a, K, V> {
    inner: IterMut<'a, K, V>,
}

/// A view into a single entry in a map, which may either be vacant or occupied.
///
/// This `enum` is constructed from the [`entry`] method on [`HashMap`].
///
/// [`HashMap`]: struct.HashMap.html
/// [`entry`]: struct.HashMap.html#method.entry
pub enum Entry<'a, K, V, S> {
    /// An occupied entry.
    Occupied(OccupiedEntry<'a, K, V, S>),

    /// A vacant entry.
    Vacant(VacantEntry<'a, K, V, S>),
}

impl<K: Debug, V: Debug, S> Debug for Entry<'_, K, V, S> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Entry::Vacant(ref v) => f.debug_tuple("Entry").field(v).finish(),
            Entry::Occupied(ref o) => f.debug_tuple("Entry").field(o).finish(),
        }
    }
}

/// A view into an occupied entry in a `HashMap`.
/// It is part of the [`Entry`] enum.
///
/// [`Entry`]: enum.Entry.html
pub struct OccupiedEntry<'a, K, V, S> {
    #[allow(dead_code)] // remove when replace_ methods are implemented
    key: Option<K>,
    elem: Bucket<(K, V)>,
    table: &'a mut HashMap<K, V, S>,
}

unsafe impl<K, V, S> Send for OccupiedEntry<'_, K, V, S>
where
    K: Send,
    V: Send,
    S: Send,
{
}
unsafe impl<K, V, S> Sync for OccupiedEntry<'_, K, V, S>
where
    K: Sync,
    V: Sync,
    S: Sync,
{
}

impl<K: Debug, V: Debug, S> Debug for OccupiedEntry<'_, K, V, S> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("OccupiedEntry")
            .field("key", self.key())
            .field("value", self.get())
            .finish()
    }
}

/// A view into a vacant entry in a `HashMap`.
/// It is part of the [`Entry`] enum.
///
/// [`Entry`]: enum.Entry.html
pub struct VacantEntry<'a, K, V, S> {
    hash: u64,
    key: K,
    table: &'a mut HashMap<K, V, S>,
}

impl<K: Debug, V, S> Debug for VacantEntry<'_, K, V, S> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("VacantEntry").field(self.key()).finish()
    }
}

impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S> {
    type Item = (&'a K, &'a V);
    type IntoIter = Iter<'a, K, V>;

    #[cfg_attr(feature = "inline-more", inline)]
    fn into_iter(self) -> Iter<'a, K, V> {
        self.iter()
    }
}

impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S> {
    type Item = (&'a K, &'a mut V);
    type IntoIter = IterMut<'a, K, V>;

    #[cfg_attr(feature = "inline-more", inline)]
    fn into_iter(self) -> IterMut<'a, K, V> {
        self.iter_mut()
    }
}

impl<K, V, S> IntoIterator for HashMap<K, V, S> {
    type Item = (K, V);
    type IntoIter = IntoIter<K, V>;

    /// Creates a consuming iterator, that is, one that moves each key-value
    /// pair out of the map in arbitrary order. The map cannot be used after
    /// calling this.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map = HashMap::new();
    /// map.insert("a", 1);
    /// map.insert("b", 2);
    /// map.insert("c", 3);
    ///
    /// // Not possible with .iter()
    /// let vec: Vec<(&str, i32)> = map.into_iter().collect();
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    fn into_iter(self) -> IntoIter<K, V> {
        IntoIter {
            inner: self.table.into_iter(),
        }
    }
}

impl<'a, K, V> Iterator for Iter<'a, K, V> {
    type Item = (&'a K, &'a V);

    #[cfg_attr(feature = "inline-more", inline)]
    fn next(&mut self) -> Option<(&'a K, &'a V)> {
        self.inner.next().map(|x| unsafe {
            let r = x.as_ref();
            (&r.0, &r.1)
        })
    }
    #[cfg_attr(feature = "inline-more", inline)]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}
impl<K, V> ExactSizeIterator for Iter<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn len(&self) -> usize {
        self.inner.len()
    }
}

impl<K, V> FusedIterator for Iter<'_, K, V> {}

impl<'a, K, V> Iterator for IterMut<'a, K, V> {
    type Item = (&'a K, &'a mut V);

    #[cfg_attr(feature = "inline-more", inline)]
    fn next(&mut self) -> Option<(&'a K, &'a mut V)> {
        self.inner.next().map(|x| unsafe {
            let r = x.as_mut();
            (&r.0, &mut r.1)
        })
    }
    #[cfg_attr(feature = "inline-more", inline)]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}
impl<K, V> ExactSizeIterator for IterMut<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn len(&self) -> usize {
        self.inner.len()
    }
}
impl<K, V> FusedIterator for IterMut<'_, K, V> {}

impl<K, V> fmt::Debug for IterMut<'_, K, V>
where
    K: fmt::Debug,
    V: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_list().entries(self.iter()).finish()
    }
}

impl<K, V> Iterator for IntoIter<K, V> {
    type Item = (K, V);

    #[cfg_attr(feature = "inline-more", inline)]
    fn next(&mut self) -> Option<(K, V)> {
        self.inner.next()
    }
    #[cfg_attr(feature = "inline-more", inline)]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}
impl<K, V> ExactSizeIterator for IntoIter<K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn len(&self) -> usize {
        self.inner.len()
    }
}
impl<K, V> FusedIterator for IntoIter<K, V> {}

impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_list().entries(self.iter()).finish()
    }
}

impl<'a, K, V> Iterator for Keys<'a, K, V> {
    type Item = &'a K;

    #[cfg_attr(feature = "inline-more", inline)]
    fn next(&mut self) -> Option<&'a K> {
        self.inner.next().map(|(k, _)| k)
    }
    #[cfg_attr(feature = "inline-more", inline)]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}
impl<K, V> ExactSizeIterator for Keys<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn len(&self) -> usize {
        self.inner.len()
    }
}
impl<K, V> FusedIterator for Keys<'_, K, V> {}

impl<'a, K, V> Iterator for Values<'a, K, V> {
    type Item = &'a V;

    #[cfg_attr(feature = "inline-more", inline)]
    fn next(&mut self) -> Option<&'a V> {
        self.inner.next().map(|(_, v)| v)
    }
    #[cfg_attr(feature = "inline-more", inline)]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}
impl<K, V> ExactSizeIterator for Values<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn len(&self) -> usize {
        self.inner.len()
    }
}
impl<K, V> FusedIterator for Values<'_, K, V> {}

impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
    type Item = &'a mut V;

    #[cfg_attr(feature = "inline-more", inline)]
    fn next(&mut self) -> Option<&'a mut V> {
        self.inner.next().map(|(_, v)| v)
    }
    #[cfg_attr(feature = "inline-more", inline)]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}
impl<K, V> ExactSizeIterator for ValuesMut<'_, K, V> {
    #[cfg_attr(feature = "inline-more", inline)]
    fn len(&self) -> usize {
        self.inner.len()
    }
}
impl<K, V> FusedIterator for ValuesMut<'_, K, V> {}

impl<K, V> fmt::Debug for ValuesMut<'_, K, V>
where
    K: fmt::Debug,
    V: fmt::Debug,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_list().entries(self.inner.iter()).finish()
    }
}

impl<'a, K, V, S> Entry<'a, K, V, S> {
    /// Sets the value of the entry, and returns an OccupiedEntry.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// let entry = map.entry("horseyland").insert(37);
    ///
    /// assert_eq!(entry.key(), &"horseyland");
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn insert(self, value: V) -> OccupiedEntry<'a, K, V, S>
    where
        K: Hash,
        S: BuildHasher,
    {
        match self {
            Entry::Occupied(mut entry) => {
                entry.insert(value);
                entry
            }
            Entry::Vacant(entry) => entry.insert_entry(value),
        }
    }

    /// Ensures a value is in the entry by inserting the default if empty, and returns
    /// a mutable reference to the value in the entry.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    ///
    /// map.entry("poneyland").or_insert(3);
    /// assert_eq!(map["poneyland"], 3);
    ///
    /// *map.entry("poneyland").or_insert(10) *= 2;
    /// assert_eq!(map["poneyland"], 6);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn or_insert(self, default: V) -> &'a mut V
    where
        K: Hash,
        S: BuildHasher,
    {
        match self {
            Entry::Occupied(entry) => entry.into_mut(),
            Entry::Vacant(entry) => entry.insert(default),
        }
    }

    /// Ensures a value is in the entry by inserting the result of the default function if empty,
    /// and returns a mutable reference to the value in the entry.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, String> = HashMap::new();
    /// let s = "hoho".to_string();
    ///
    /// map.entry("poneyland").or_insert_with(|| s);
    ///
    /// assert_eq!(map["poneyland"], "hoho".to_string());
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn or_insert_with<F: FnOnce() -> V>(self, default: F) -> &'a mut V
    where
        K: Hash,
        S: BuildHasher,
    {
        match self {
            Entry::Occupied(entry) => entry.into_mut(),
            Entry::Vacant(entry) => entry.insert(default()),
        }
    }

    /// Ensures a value is in the entry by inserting, if empty, the result of the default function,
    /// which takes the key as its argument, and returns a mutable reference to the value in the
    /// entry.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, usize> = HashMap::new();
    ///
    /// map.entry("poneyland").or_insert_with_key(|key| key.chars().count());
    ///
    /// assert_eq!(map["poneyland"], 9);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn or_insert_with_key<F: FnOnce(&K) -> V>(self, default: F) -> &'a mut V
    where
        K: Hash,
        S: BuildHasher,
    {
        match self {
            Entry::Occupied(entry) => entry.into_mut(),
            Entry::Vacant(entry) => {
                let value = default(entry.key());
                entry.insert(value)
            }
        }
    }

    /// Returns a reference to this entry's key.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn key(&self) -> &K {
        match *self {
            Entry::Occupied(ref entry) => entry.key(),
            Entry::Vacant(ref entry) => entry.key(),
        }
    }

    /// Provides in-place mutable access to an occupied entry before any
    /// potential inserts into the map.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    ///
    /// map.entry("poneyland")
    ///    .and_modify(|e| { *e += 1 })
    ///    .or_insert(42);
    /// assert_eq!(map["poneyland"], 42);
    ///
    /// map.entry("poneyland")
    ///    .and_modify(|e| { *e += 1 })
    ///    .or_insert(42);
    /// assert_eq!(map["poneyland"], 43);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn and_modify<F>(self, f: F) -> Self
    where
        F: FnOnce(&mut V),
    {
        match self {
            Entry::Occupied(mut entry) => {
                f(entry.get_mut());
                Entry::Occupied(entry)
            }
            Entry::Vacant(entry) => Entry::Vacant(entry),
        }
    }
}

impl<'a, K, V: Default, S> Entry<'a, K, V, S> {
    /// Ensures a value is in the entry by inserting the default value if empty,
    /// and returns a mutable reference to the value in the entry.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, Option<u32>> = HashMap::new();
    /// map.entry("poneyland").or_default();
    ///
    /// assert_eq!(map["poneyland"], None);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn or_default(self) -> &'a mut V
    where
        K: Hash,
        S: BuildHasher,
    {
        match self {
            Entry::Occupied(entry) => entry.into_mut(),
            Entry::Vacant(entry) => entry.insert(Default::default()),
        }
    }
}

impl<'a, K, V, S> OccupiedEntry<'a, K, V, S> {
    /// Gets a reference to the key in the entry.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// map.entry("poneyland").or_insert(12);
    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn key(&self) -> &K {
        unsafe { &self.elem.as_ref().0 }
    }

    /// Take the ownership of the key and value from the map.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// map.entry("poneyland").or_insert(12);
    ///
    /// if let Entry::Occupied(o) = map.entry("poneyland") {
    ///     // We delete the entry from the map.
    ///     o.remove_entry();
    /// }
    ///
    /// assert_eq!(map.contains_key("poneyland"), false);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn remove_entry(self) -> (K, V) {
        unsafe {
            // Read the item before the erase, in case erase reclaims memory.
            let v = self.elem.read();
            self.table.table.erase_no_drop(&self.elem);
            v
        }
    }

    /// Gets a reference to the value in the entry.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// map.entry("poneyland").or_insert(12);
    ///
    /// if let Entry::Occupied(o) = map.entry("poneyland") {
    ///     assert_eq!(o.get(), &12);
    /// }
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn get(&self) -> &V {
        unsafe { &self.elem.as_ref().1 }
    }

    /// Gets a mutable reference to the value in the entry.
    ///
    /// If you need a reference to the `OccupiedEntry` which may outlive the
    /// destruction of the `Entry` value, see [`into_mut`].
    ///
    /// [`into_mut`]: #method.into_mut
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// map.entry("poneyland").or_insert(12);
    ///
    /// assert_eq!(map["poneyland"], 12);
    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
    ///     *o.get_mut() += 10;
    ///     assert_eq!(*o.get(), 22);
    ///
    ///     // We can use the same Entry multiple times.
    ///     *o.get_mut() += 2;
    /// }
    ///
    /// assert_eq!(map["poneyland"], 24);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn get_mut(&mut self) -> &mut V {
        unsafe { &mut self.elem.as_mut().1 }
    }

    /// Converts the OccupiedEntry into a mutable reference to the value in the entry
    /// with a lifetime bound to the map itself.
    ///
    /// If you need multiple references to the `OccupiedEntry`, see [`get_mut`].
    ///
    /// [`get_mut`]: #method.get_mut
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// map.entry("poneyland").or_insert(12);
    ///
    /// assert_eq!(map["poneyland"], 12);
    /// if let Entry::Occupied(o) = map.entry("poneyland") {
    ///     *o.into_mut() += 10;
    /// }
    ///
    /// assert_eq!(map["poneyland"], 22);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn into_mut(self) -> &'a mut V {
        unsafe { &mut self.elem.as_mut().1 }
    }

    /// Sets the value of the entry, and returns the entry's old value.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// map.entry("poneyland").or_insert(12);
    ///
    /// if let Entry::Occupied(mut o) = map.entry("poneyland") {
    ///     assert_eq!(o.insert(15), 12);
    /// }
    ///
    /// assert_eq!(map["poneyland"], 15);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn insert(&mut self, mut value: V) -> V {
        let old_value = self.get_mut();
        mem::swap(&mut value, old_value);
        value
    }

    /// Takes the value out of the entry, and returns it.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// map.entry("poneyland").or_insert(12);
    ///
    /// if let Entry::Occupied(o) = map.entry("poneyland") {
    ///     assert_eq!(o.remove(), 12);
    /// }
    ///
    /// assert_eq!(map.contains_key("poneyland"), false);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn remove(self) -> V {
        self.remove_entry().1
    }

    // NOTE:
    // replace_entry and replace_key are _not_ okay, because it may move a bucket in the old
    // table to _before_ where the "move keys iterator" is currently pointed. in which case we'd
    // fail to move them.
    //
    // it should be possible to work around this by checking if that's the case, and then
    // restarting the iterator, though that would come at a performance penalty...
    //
    // when implemented, remove the #[allow(dead_code)] on OccupiedEntry::key
}

impl<'a, K, V, S> VacantEntry<'a, K, V, S> {
    /// Gets a reference to the key that would be used when inserting a value
    /// through the `VacantEntry`.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    /// assert_eq!(map.entry("poneyland").key(), &"poneyland");
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn key(&self) -> &K {
        &self.key
    }

    /// Take ownership of the key.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    ///
    /// if let Entry::Vacant(v) = map.entry("poneyland") {
    ///     v.into_key();
    /// }
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn into_key(self) -> K {
        self.key
    }

    /// Sets the value of the entry with the VacantEntry's key,
    /// and returns a mutable reference to it.
    ///
    /// # Examples
    ///
    /// ```
    /// use griddle::HashMap;
    /// use griddle::hash_map::Entry;
    ///
    /// let mut map: HashMap<&str, u32> = HashMap::new();
    ///
    /// if let Entry::Vacant(o) = map.entry("poneyland") {
    ///     o.insert(37);
    /// }
    /// assert_eq!(map["poneyland"], 37);
    /// ```
    #[cfg_attr(feature = "inline-more", inline)]
    pub fn insert(self, value: V) -> &'a mut V
    where
        K: Hash,
        S: BuildHasher,
    {
        let hash_builder = &self.table.hash_builder;
        let bucket = self.table.table.insert(self.hash, (self.key, value), |x| {
            make_hash(hash_builder, &x.0)
        });
        unsafe { &mut bucket.as_mut().1 }
    }

    #[cfg_attr(feature = "inline-more", inline)]
    fn insert_entry(self, value: V) -> OccupiedEntry<'a, K, V, S>
    where
        K: Hash,
        S: BuildHasher,
    {
        let hash_builder = &self.table.hash_builder;
        let elem = self.table.table.insert(self.hash, (self.key, value), |x| {
            make_hash(hash_builder, &x.0)
        });
        OccupiedEntry {
            key: None,
            elem,
            table: self.table,
        }
    }
}

impl<K, V, S> FromIterator<(K, V)> for HashMap<K, V, S>
where
    K: Eq + Hash,
    S: BuildHasher + Default,
{
    #[cfg_attr(feature = "inline-more", inline)]
    fn from_iter<T: IntoIterator<Item = (K, V)>>(iter: T) -> Self {
        let iter = iter.into_iter();
        let mut map = Self::with_capacity_and_hasher(iter.size_hint().0, S::default());
        iter.for_each(|(k, v)| {
            map.insert(k, v);
        });
        map
    }
}

/// Inserts all new key-values from the iterator and replaces values with existing
/// keys with new values returned from the iterator.
impl<K, V, S> Extend<(K, V)> for HashMap<K, V, S>
where
    K: Eq + Hash,
    S: BuildHasher,
{
    #[cfg_attr(feature = "inline-more", inline)]
    fn extend<T: IntoIterator<Item = (K, V)>>(&mut self, iter: T) {
        // Keys may be already present or show multiple times in the iterator.
        // Reserve the entire hint lower bound if the map is empty.
        // Otherwise reserve half the hint (rounded up), so the map
        // will only resize twice in the worst case.
        let iter = iter.into_iter();
        let reserve = if self.is_empty() {
            iter.size_hint().0
        } else {
            (iter.size_hint().0 + 1) / 2
        };
        self.reserve(reserve);
        iter.for_each(move |(k, v)| {
            self.insert(k, v);
        });
    }
}

impl<'a, K, V, S> Extend<(&'a K, &'a V)> for HashMap<K, V, S>
where
    K: Eq + Hash + Copy,
    V: Copy,
    S: BuildHasher,
{
    #[cfg_attr(feature = "inline-more", inline)]
    fn extend<T: IntoIterator<Item = (&'a K, &'a V)>>(&mut self, iter: T) {
        self.extend(iter.into_iter().map(|(&key, &value)| (key, value)));
    }
}

#[allow(dead_code)]
fn assert_covariance() {
    fn map_key<'new>(v: HashMap<&'static str, u8>) -> HashMap<&'new str, u8> {
        v
    }
    fn map_val<'new>(v: HashMap<u8, &'static str>) -> HashMap<u8, &'new str> {
        v
    }
    fn iter_key<'a, 'new>(v: Iter<'a, &'static str, u8>) -> Iter<'a, &'new str, u8> {
        v
    }
    fn iter_val<'a, 'new>(v: Iter<'a, u8, &'static str>) -> Iter<'a, u8, &'new str> {
        v
    }
    fn into_iter_key<'new>(v: IntoIter<&'static str, u8>) -> IntoIter<&'new str, u8> {
        v
    }
    fn into_iter_val<'new>(v: IntoIter<u8, &'static str>) -> IntoIter<u8, &'new str> {
        v
    }
    fn keys_key<'a, 'new>(v: Keys<'a, &'static str, u8>) -> Keys<'a, &'new str, u8> {
        v
    }
    fn keys_val<'a, 'new>(v: Keys<'a, u8, &'static str>) -> Keys<'a, u8, &'new str> {
        v
    }
    fn values_key<'a, 'new>(v: Values<'a, &'static str, u8>) -> Values<'a, &'new str, u8> {
        v
    }
    fn values_val<'a, 'new>(v: Values<'a, u8, &'static str>) -> Values<'a, u8, &'new str> {
        v
    }
}

#[cfg(test)]
#[cfg(not(tarpaulin_include))] // don't count for coverage
mod test_map {
    use super::DefaultHashBuilder;
    use super::Entry::{Occupied, Vacant};
    use super::HashMap;
    use crate::TryReserveError::*;
    use rand::{rngs::SmallRng, Rng, SeedableRng};
    use std::cell::RefCell;
    use std::usize;
    use std::vec::Vec;

    #[test]
    fn test_zero_capacities() {
        type HM = HashMap<i32, i32>;

        let m = HM::new();
        assert_eq!(m.capacity(), 0);

        let m = HM::default();
        assert_eq!(m.capacity(), 0);

        let m = HM::with_hasher(DefaultHashBuilder::default());
        assert_eq!(m.capacity(), 0);

        let m = HM::with_capacity(0);
        assert_eq!(m.capacity(), 0);

        let m = HM::with_capacity_and_hasher(0, DefaultHashBuilder::default());
        assert_eq!(m.capacity(), 0);

        let mut m = HM::new();
        m.insert(1, 1);
        m.insert(2, 2);
        m.remove(&1);
        m.remove(&2);
        m.shrink_to_fit();
        assert_eq!(m.capacity(), 0);

        let mut m = HM::new();
        m.reserve(0);
        assert_eq!(m.capacity(), 0);
    }

    #[test]
    fn test_create_capacity_zero() {
        let mut m = HashMap::with_capacity(0);

        assert!(m.insert(1, 1).is_none());

        assert!(m.contains_key(&1));
        assert!(!m.contains_key(&0));
    }

    #[test]
    fn test_insert() {
        let mut m = HashMap::new();
        assert_eq!(m.len(), 0);
        assert!(m.insert(1, 2).is_none());
        assert_eq!(m.len(), 1);
        assert!(m.insert(2, 4).is_none());
        assert_eq!(m.len(), 2);
        assert_eq!(*m.get(&1).unwrap(), 2);
        assert_eq!(*m.get(&2).unwrap(), 4);
    }

    #[test]
    fn test_split_insert() {
        // the code below assumes that R is 4
        assert_eq!(crate::raw::R, 4);

        let mut m = HashMap::new();
        assert_eq!(m.capacity(), 0);
        // three inserts won't split
        for i in 1..=3 {
            m.insert(i, i);
            assert_eq!(m.get(&i), Some(&i));
            assert_eq!(m.capacity(), 3);
        }
        // fourth insert will split and migrate all elements
        assert!(!m.is_split());
        m.insert(4, 4);
        // capacity should now be doubled
        assert_eq!(m.capacity(), 7);
        // and there should be no leftovers
        assert!(!m.is_split());
        assert_eq!(m.table.len(), 4);
        for i in 1..=4 {
            assert_eq!(m.get(&i), Some(&i));
        }

        // move to next split point
        for i in 5..=7 {
            m.insert(i, i);
            assert_eq!(m.get(&i), Some(&i));
            assert_eq!(m.capacity(), 7);
        }

        // next insert will split, and move some, but not all (since R < old.len())
        m.insert(8, 8);
        // capacity should now be doubled
        assert_eq!(m.capacity(), 14);
        // and there should be leftovers
        assert!(m.is_split());
        assert_eq!(m.table.main().len(), 1 + crate::raw::R);
        assert_eq!(
            m.table.leftovers().map(|t| t.len()),
            Some(8 - (1 + crate::raw::R))
        );
        for i in 1..=8 {
            assert_eq!(m.get(&i), Some(&i));
        }
        // check that the iterators do the right thing when split:
        assert_eq!(m.iter().count(), 8);
        for i in 1..=8 {
            assert!(m.iter().any(|(&e, _)| e == i));
        }
        assert_eq!(m.iter_mut().count(), 8);
        for i in 1..=8 {
            assert!(m.iter_mut().any(|(&e, _)| e == i));
        }

        // if we do another insert, it will move the rest of the items from the old map
        m.insert(9, 9);
        assert!(!m.is_split());
        assert_eq!(m.table.len(), 9);
        // it should not have changed capacity
        assert_eq!(m.capacity(), 14);
        for i in 1..=9 {
            assert_eq!(m.get(&i), Some(&i));
        }
    }

    #[test]
    fn test_clone() {
        let mut m = HashMap::new();
        for i in 1..=8 {
            assert_eq!(m.len(), i - 1);
            assert!(m.insert(i, i + 1).is_none());
        }
        assert_eq!(m.len(), 8);
        let m2 = m.clone();
        for i in 1..=8 {
            assert_eq!(m2.get(&i).copied(), Some(i + 1));
        }
        assert_eq!(m2.len(), 8);
    }

    #[test]
    fn test_clone_from() {
        let mut m = HashMap::new();
        let mut m2 = HashMap::new();
        for i in 1..=8 {
            assert_eq!(m.len(), i - 1);
            assert!(m.insert(i, i + 1).is_none());
        }
        assert_eq!(m.len(), 8);
        m2.clone_from(&m);
        for i in 1..=8 {
            assert_eq!(m2.get(&i).copied(), Some(i + 1));
        }
        assert_eq!(m2.len(), 8);
    }

    thread_local! { static DROP_VECTOR: RefCell<Vec<i32>> = RefCell::new(Vec::new()) }

    #[derive(Hash, PartialEq, Eq)]
    struct Droppable {
        k: usize,
    }

    impl Droppable {
        fn new(k: usize) -> Droppable {
            DROP_VECTOR.with(|slot| {
                slot.borrow_mut()[k] += 1;
            });

            Droppable { k }
        }
    }

    impl Drop for Droppable {
        fn drop(&mut self) {
            DROP_VECTOR.with(|slot| {
                slot.borrow_mut()[self.k] -= 1;
            });
        }
    }

    impl Clone for Droppable {
        fn clone(&self) -> Self {
            Droppable::new(self.k)
        }
    }

    #[test]
    fn test_drops() {
        DROP_VECTOR.with(|slot| {
            *slot.borrow_mut() = vec![0; 200];
        });

        {
            let mut m = HashMap::new();

            DROP_VECTOR.with(|v| {
                for i in 0..200 {
                    assert_eq!(v.borrow()[i], 0);
                }
            });

            for i in 0..100 {
                let d1 = Droppable::new(i);
                let d2 = Droppable::new(i + 100);
                m.insert(d1, d2);
            }

            DROP_VECTOR.with(|v| {
                for i in 0..200 {
                    assert_eq!(v.borrow()[i], 1);
                }
            });

            for i in 0..50 {
                let k = Droppable::new(i);
                let v = m.remove(&k);

                assert!(v.is_some());

                DROP_VECTOR.with(|v| {
                    assert_eq!(v.borrow()[i], 1);
                    assert_eq!(v.borrow()[i + 100], 1);
                });
            }

            DROP_VECTOR.with(|v| {
                for i in 0..50 {
                    assert_eq!(v.borrow()[i], 0);
                    assert_eq!(v.borrow()[i + 100], 0);
                }

                for i in 50..100 {
                    assert_eq!(v.borrow()[i], 1);
                    assert_eq!(v.borrow()[i + 100], 1);
                }
            });
        }

        DROP_VECTOR.with(|v| {
            for i in 0..200 {
                assert_eq!(v.borrow()[i], 0);
            }
        });
    }

    #[test]
    fn test_into_iter_drops() {
        DROP_VECTOR.with(|v| {
            *v.borrow_mut() = vec![0; 200];
        });

        let hm = {
            let mut hm = HashMap::new();

            DROP_VECTOR.with(|v| {
                for i in 0..200 {
                    assert_eq!(v.borrow()[i], 0);
                }
            });

            for i in 0..100 {
                let d1 = Droppable::new(i);
                let d2 = Droppable::new(i + 100);
                hm.insert(d1, d2);
            }

            DROP_VECTOR.with(|v| {
                for i in 0..200 {
                    assert_eq!(v.borrow()[i], 1);
                }
            });

            hm
        };

        // By the way, ensure that cloning doesn't screw up the dropping.
        drop(hm.clone());

        {
            let mut half = hm.into_iter().take(50);

            DROP_VECTOR.with(|v| {
                for i in 0..200 {
                    assert_eq!(v.borrow()[i], 1);
                }
            });

            for _ in half.by_ref() {}

            DROP_VECTOR.with(|v| {
                let nk = (0..100).filter(|&i| v.borrow()[i] == 1).count();

                let nv = (0..100).filter(|&i| v.borrow()[i + 100] == 1).count();

                assert_eq!(nk, 50);
                assert_eq!(nv, 50);
            });
        };

        DROP_VECTOR.with(|v| {
            for i in 0..200 {
                assert_eq!(v.borrow()[i], 0);
            }
        });
    }

    #[test]
    fn test_empty_remove() {
        let mut m: HashMap<i32, bool> = HashMap::new();
        assert_eq!(m.remove(&0), None);
    }

    #[test]
    fn test_empty_entry() {
        let mut m: HashMap<i32, bool> = HashMap::new();
        match m.entry(0) {
            Occupied(_) => panic!(),
            Vacant(_) => {}
        }
        assert!(*m.entry(0).or_insert(true));
        assert_eq!(m.len(), 1);
    }

    #[test]
    fn test_empty_iter() {
        let mut m: HashMap<i32, bool> = HashMap::new();
        assert_eq!(m.keys().next(), None);
        assert_eq!(m.values().next(), None);
        assert_eq!(m.values_mut().next(), None);
        assert_eq!(m.iter().next(), None);
        assert_eq!(m.iter_mut().next(), None);
        assert_eq!(m.len(), 0);
        assert!(m.is_empty());
        assert_eq!(m.into_iter().next(), None);
    }

    #[test]
    fn test_lots_of_insertions() {
        let mut m = HashMap::new();

        #[cfg(not(any(tarpaulin, miri)))]
        const N: usize = 10;
        #[cfg(any(tarpaulin, miri))]
        const N: usize = 5;

        #[cfg(not(any(tarpaulin, miri)))]
        const M: usize = 1001;
        #[cfg(tarpaulin)]
        const M: usize = 101;
        #[cfg(miri)]
        const M: usize = 16;

        // Try this a few times to make sure we never screw up the hashmap's
        // internal state.
        for _ in 0..N {
            assert!(m.is_empty());

            for i in 1..M {
                assert!(m.insert(i, i).is_none());

                for j in 1..=i {
                    let r = m.get(&j);
                    assert_eq!(r, Some(&j));
                }

                for j in i + 1..M {
                    let r = m.get(&j);
                    assert_eq!(r, None);
                }
            }

            for i in M..(M * 2 - 1) {
                assert!(!m.contains_key(&i));
            }

            // remove forwards
            for i in 1..M {
                assert!(m.remove(&i).is_some());

                for j in 1..=i {
                    assert!(!m.contains_key(&j));
                }

                for j in i + 1..M {
                    assert!(m.contains_key(&j));
                }
            }

            for i in 1..M {
                assert!(!m.contains_key(&i));
            }

            for i in 1..M {
                assert!(m.insert(i, i).is_none());
            }

            // remove backwards
            for i in (1..M).rev() {
                assert!(m.remove(&i).is_some());

                for j in i..M {
                    assert!(!m.contains_key(&j));
                }

                for j in 1..i {
                    assert!(m.contains_key(&j));
                }
            }
        }
    }

    #[test]
    fn test_find_mut() {
        let mut m = HashMap::new();
        // ensure that the map splits
        for i in 1..=6 {
            m.insert(1000 + i, i);
        }
        assert!(!m.is_split());
        assert!(m.insert(1, 12).is_none());
        assert!(!m.is_split());
        assert!(m.insert(2, 8).is_none());
        assert!(m.is_split());
        assert!(m.insert(5, 14).is_none());
        let new = 100;
        match m.get_mut(&5) {
            None => panic!(),
            Some(x) => *x = new,
        }
        assert_eq!(m.get(&5), Some(&new));
    }

    #[test]
    fn test_insert_overwrite() {
        let mut m = HashMap::new();
        // ensure that the map splits
        for i in 1..=7 {
            m.insert(1000 + i, i);
        }
        assert!(!m.is_split());
        assert!(m.insert(1, 2).is_none());
        assert!(m.is_split());
        assert_eq!(*m.get(&1).unwrap(), 2);
        assert!(!m.insert(1, 3).is_none());
        assert_eq!(*m.get(&1).unwrap(), 3);
    }

    #[test]
    fn test_insert_conflicts() {
        let mut m = HashMap::with_capacity(4);
        // ensure that the map splits
        for i in 1..=7 {
            m.insert(1000 + i, i);
        }
        assert!(!m.is_split());
        assert!(m.insert(1, 2).is_none());
        assert!(m.is_split());
        assert!(m.insert(5, 3).is_none());
        assert!(m.insert(9, 4).is_none());
        assert_eq!(*m.get(&9).unwrap(), 4);
        assert_eq!(*m.get(&5).unwrap(), 3);
        assert_eq!(*m.get(&1).unwrap(), 2);
    }

    #[test]
    fn test_conflict_remove() {
        let mut m = HashMap::with_capacity(4);
        // ensure that the map splits
        for i in 1..=5 {
            m.insert(1000 + i, i);
        }
        assert!(!m.is_split());
        assert!(m.insert(1, 2).is_none());
        assert_eq!(*m.get(&1).unwrap(), 2);
        assert!(m.insert(5, 3).is_none());
        assert!(!m.is_split());
        assert_eq!(*m.get(&1).unwrap(), 2);
        assert_eq!(*m.get(&5).unwrap(), 3);
        assert!(m.insert(9, 4).is_none());
        assert!(m.is_split());
        assert_eq!(*m.get(&1).unwrap(), 2);
        assert_eq!(*m.get(&5).unwrap(), 3);
        assert_eq!(*m.get(&9).unwrap(), 4);
        assert!(m.remove(&1).is_some());
        assert_eq!(*m.get(&9).unwrap(), 4);
        assert_eq!(*m.get(&5).unwrap(), 3);
    }

    #[test]
    fn test_is_empty() {
        let mut m = HashMap::with_capacity(4);
        assert!(m.insert(1, 2).is_none());
        assert!(!m.is_empty());
        assert!(m.remove(&1).is_some());
        assert!(m.is_empty());
    }

    #[test]
    fn test_remove() {
        let mut m = HashMap::new();
        m.insert(1, 2);
        assert_eq!(m.remove(&1), Some(2));
        assert_eq!(m.remove(&1), None);
    }

    #[test]
    fn test_remove_entry() {
        let mut m = HashMap::new();
        m.insert(1, 2);
        assert_eq!(m.remove_entry(&1), Some((1, 2)));
        assert_eq!(m.remove(&1), None);
    }

    #[test]
    fn test_iterate() {
        let mut m = HashMap::with_capacity(4);
        for i in 0..32 {
            assert!(m.insert(i, i * 2).is_none());
        }
        assert!(m.is_split());
        assert_eq!(m.len(), 32);

        let mut observed: u32 = 0;

        for (k, v) in &m {
            assert_eq!(*v, *k * 2);
            observed |= 1 << *k;
        }
        assert_eq!(observed, 0xFFFF_FFFF);
    }

    #[test]
    fn test_keys() {
        let mut map = HashMap::new();
        for (k, v) in (1..).zip(1000..).take(8) {
            map.insert(k, v);
        }
        assert!(map.is_split());
        let keys: Vec<_> = map.keys().cloned().collect();
        assert_eq!(keys.len(), 8);
        for i in 1..=8 {
            assert!(keys.contains(&i));
        }
    }

    #[test]
    fn test_values() {
        let mut map = HashMap::new();
        for (k, v) in (1..).zip(1000..).take(8) {
            map.insert(k, v);
        }
        assert!(map.is_split());
        let values: Vec<_> = map.values().cloned().collect();
        assert_eq!(values.len(), 8);
        for c in 1000..=1007 {
            assert!(values.contains(&c));
        }
    }

    #[test]
    fn test_values_mut() {
        let mut map = HashMap::new();
        for v in (1..).take(8) {
            map.insert(v, v);
        }
        assert!(map.is_split());
        for value in map.values_mut() {
            *value = (*value) * 2
        }
        let values: Vec<_> = map.values().cloned().collect();
        assert_eq!(values.len(), 8);
        for v in 1..=8 {
            let v = 2 * v;
            assert!(values.contains(&v));
        }
    }

    #[test]
    fn test_find() {
        let mut m = HashMap::new();
        assert!(m.get(&1).is_none());
        m.insert(1, 2);
        match m.get(&1) {
            None => panic!(),
            Some(v) => assert_eq!(*v, 2),
        }
        assert!(!m.is_split());

        // now make it split
        for i in 1..=7 {
            m.insert(1000 + i, i);
        }
        assert!(m.is_split());
        match m.get(&1) {
            None => panic!(),
            Some(v) => assert_eq!(*v, 2),
        }

        // now make it un-split
        m.insert(1000 + 8, 8);
        assert!(!m.is_split());
        match m.get(&1) {
            None => panic!(),
            Some(v) => assert_eq!(*v, 2),
        }
    }

    #[test]
    fn test_eq() {
        let mut m1 = HashMap::new();
        for (k, v) in (1..).zip(1000..).take(8) {
            m1.insert(k, v);
        }

        let mut m2 = HashMap::new();
        for (k, v) in (1..).zip(1000..).take(7) {
            m2.insert(k, v);
        }

        assert!(m1 != m2);

        m2.insert(8, 1007);

        assert_eq!(m1, m2);
    }

    #[test]
    fn test_show() {
        let mut map = HashMap::new();
        let empty: HashMap<i32, i32> = HashMap::new();

        map.insert(1, 2);
        map.insert(3, 4);

        let map_str = format!("{:?}", map);

        assert!(map_str == "{1: 2, 3: 4}" || map_str == "{3: 4, 1: 2}");
        assert_eq!(format!("{:?}", empty), "{}");
    }

    #[test]
    fn test_expand() {
        let mut m = HashMap::new();

        assert_eq!(m.len(), 0);
        assert!(m.is_empty());

        let mut i = 0;
        let old_raw_cap = m.raw_capacity();
        while old_raw_cap == m.raw_capacity() {
            m.insert(i, i);
            i += 1;
        }

        assert_eq!(m.len(), i);
        assert!(!m.is_empty());
    }

    #[test]
    fn test_reserve_shrink_to_fit() {
        let mut m = HashMap::new();
        m.insert(0, 0);
        m.remove(&0);
        assert!(m.capacity() >= m.len());
        for i in 0..128 {
            m.insert(i, i);
        }
        assert!(m.is_split());
        m.reserve(256);

        let usable_cap = m.capacity();
        for i in 128..(128 + 256) {
            m.insert(i, i);
            assert_eq!(m.capacity(), usable_cap);
        }

        for i in 100..(128 + 256) {
            assert_eq!(m.remove(&i), Some(i));
        }
        m.shrink_to_fit();

        assert_eq!(m.len(), 100);
        assert!(!m.is_empty());
        assert!(m.capacity() >= m.len());

        for i in 0..100 {
            assert_eq!(m.remove(&i), Some(i));
        }
        m.shrink_to_fit();
        m.insert(0, 0);

        assert_eq!(m.len(), 1);
        assert!(m.capacity() >= m.len());
        assert_eq!(m.remove(&0), Some(0));
    }

    #[test]
    fn test_from_iter() {
        let xs = (0..8).map(|v| (v, v));

        let map: HashMap<_, _> = xs.clone().collect();

        for (k, v) in xs.clone() {
            assert_eq!(map.get(&k), Some(&v));
        }

        assert_eq!(map.iter().len(), xs.len());
    }

    #[test]
    fn test_size_hint() {
        let xs = (0..8).map(|v| (v, v));

        let map: HashMap<_, _> = xs.clone().collect();

        let mut iter = map.iter();

        for _ in iter.by_ref().take(3) {}

        assert_eq!(iter.size_hint(), (8 - 3, Some(8 - 3)));
    }

    #[test]
    fn test_iter_len() {
        let xs = (0..8).map(|v| (v, v));

        let map: HashMap<_, _> = xs.clone().collect();

        let mut iter = map.iter();

        for _ in iter.by_ref().take(3) {}

        assert_eq!(iter.len(), 8 - 3);
    }

    #[test]
    fn test_mut_size_hint() {
        let xs = (0..8).map(|v| (v, v));

        let mut map: HashMap<_, _> = xs.clone().collect();

        let mut iter = map.iter_mut();

        for _ in iter.by_ref().take(3) {}

        assert_eq!(iter.size_hint(), (8 - 3, Some(8 - 3)));
    }

    #[test]
    fn test_iter_mut_len() {
        let xs = (0..8).map(|v| (v, v));

        let mut map: HashMap<_, _> = xs.clone().collect();

        let mut iter = map.iter_mut();

        for _ in iter.by_ref().take(3) {}

        assert_eq!(iter.len(), 8 - 3);
    }

    #[test]
    fn test_index() {
        let mut map = HashMap::new();

        for i in 1..=8 {
            map.insert(i, i);
        }
        assert!(map.is_split());

        assert_eq!(map[&2], 2);
    }

    #[test]
    #[should_panic]
    fn test_index_nonexistent() {
        let mut map = HashMap::new();

        for i in 1..=8 {
            map.insert(i, i);
        }
        assert!(map.is_split());

        map[&9];
    }

    #[test]
    fn test_entry() {
        let xs = (1..9).map(|v| (v, 10 * v));

        let mut map: HashMap<_, _> = xs.clone().collect();

        // Existing key (insert)
        match map.entry(1) {
            Vacant(_) => unreachable!(),
            Occupied(mut view) => {
                assert_eq!(view.get(), &10);
                assert_eq!(view.insert(100), 10);
            }
        }
        assert_eq!(map.get(&1).unwrap(), &100);
        assert_eq!(map.len(), 8);

        // Existing key (update; old table)
        match map.entry(2) {
            Vacant(_) => unreachable!(),
            Occupied(mut view) => {
                let v = view.get_mut();
                let new_v = (*v) * 10;
                *v = new_v;
            }
        }
        assert_eq!(map.get(&2).unwrap(), &200);
        assert_eq!(map.len(), 8);

        // Existing key (update; new table)
        match map.entry(8) {
            Vacant(_) => unreachable!(),
            Occupied(mut view) => {
                let v = view.get_mut();
                let new_v = (*v) * 10;
                *v = new_v;
            }
        }
        assert_eq!(map.get(&8).unwrap(), &800);
        assert_eq!(map.len(), 8);

        // Existing key (take)
        match map.entry(3) {
            Vacant(_) => unreachable!(),
            Occupied(view) => {
                assert_eq!(view.remove(), 30);
            }
        }
        assert_eq!(map.get(&3), None);
        assert_eq!(map.len(), 7);

        // Inexistent key (insert)
        match map.entry(10) {
            Occupied(_) => unreachable!(),
            Vacant(view) => {
                assert_eq!(*view.insert(1000), 1000);
            }
        }
        assert_eq!(map.get(&10).unwrap(), &1000);
        assert_eq!(map.len(), 8);
    }

    #[test]
    fn test_entry_take_doesnt_corrupt() {
        #![allow(deprecated)] //rand
                              // Test for #19292
        fn check(m: &HashMap<i32, ()>) {
            for k in m.keys() {
                assert!(m.contains_key(k), "{} is in keys() but not in the map?", k);
            }
        }

        let mut m = HashMap::new();

        let mut rng = {
            let seed = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
            SmallRng::from_seed(seed)
        };

        // Populate the map with some items.
        for _ in 0..50 {
            let x = rng.gen_range(-10, 10);
            m.insert(x, ());
        }

        for _ in 0..1000 {
            let x = rng.gen_range(-10, 10);
            match m.entry(x) {
                Vacant(_) => {}
                Occupied(e) => {
                    e.remove();
                }
            }

            check(&m);
        }
    }

    #[test]
    fn test_extend_ref() {
        let mut a = HashMap::new();
        a.insert(1, "one");
        let mut b = HashMap::new();
        b.insert(2, "two");
        b.insert(3, "three");

        a.extend(&b);

        assert_eq!(a.len(), 3);
        assert_eq!(a[&1], "one");
        assert_eq!(a[&2], "two");
        assert_eq!(a[&3], "three");
    }

    #[test]
    fn test_capacity_not_less_than_len() {
        let mut a = HashMap::new();
        let mut item = 0;

        for _ in 0..116 {
            a.insert(item, 0);
            item += 1;
        }

        assert!(a.capacity() > a.len());

        let free = a.capacity() - a.len();
        for _ in 0..free {
            a.insert(item, 0);
            item += 1;
        }

        assert_eq!(a.len(), a.capacity());

        // Insert at capacity should cause allocation.
        a.insert(item, 0);
        assert!(a.capacity() > a.len());
    }

    #[test]
    fn test_occupied_entry_key() {
        let mut a = HashMap::new();
        let key = "hello there";
        let value = "value goes here";
        assert!(a.is_empty());
        a.insert(key.clone(), value.clone());
        assert_eq!(a.len(), 1);
        assert_eq!(a[key], value);

        match a.entry(key.clone()) {
            Vacant(_) => panic!(),
            Occupied(e) => assert_eq!(key, *e.key()),
        }
        assert_eq!(a.len(), 1);
        assert_eq!(a[key], value);
    }

    #[test]
    fn test_vacant_entry_key() {
        let mut a = HashMap::new();
        let key = "hello there";
        let value = "value goes here";

        assert!(a.is_empty());
        match a.entry(key.clone()) {
            Occupied(_) => panic!(),
            Vacant(e) => {
                assert_eq!(key, *e.key());
                e.insert(value.clone());
            }
        }
        assert_eq!(a.len(), 1);
        assert_eq!(a[key], value);
    }

    #[test]
    fn test_retain() {
        let mut map: HashMap<i32, i32> = HashMap::new();
        for x in 0..120 {
            map.insert(x, x * 10);
        }
        assert!(map.is_split());

        map.retain(|&k, _| k % 2 == 0);
        assert_eq!(map.len(), 60);
        assert_eq!(map[&2], 20);
        assert_eq!(map[&4], 40);
        assert_eq!(map[&6], 60);
    }

    #[test]
    #[cfg_attr(miri, ignore)] // FIXME: no OOM signalling (https://github.com/rust-lang/miri/issues/613)
    fn test_try_reserve() {
        let mut empty_bytes: HashMap<u8, u8> = HashMap::new();

        const MAX_USIZE: usize = usize::MAX;

        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE) {
        } else {
            panic!("usize::MAX should trigger an overflow!");
        }

        if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE / 8) {
        } else {
            // This may succeed if there is enough free memory. Attempt to
            // allocate a second hashmap to ensure the allocation will fail.
            let mut empty_bytes2: HashMap<u8, u8> = HashMap::new();
            if let Err(AllocError { .. }) = empty_bytes2.try_reserve(MAX_USIZE / 8) {
            } else {
                panic!("usize::MAX / 8 should trigger an OOM!");
            }
        }
    }
}