Struct HashMap 

pub struct HashMap<K, V, S = FxBuildHasher>(/* private fields */);

A hash map implemented with quadratic probing.

Implementations

impl<K, V> HashMap<K, V, FxBuildHasher>

pub fn new() -> HashMap<K, V, FxBuildHasher>

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.

impl<K, V, S> HashMap<K, V, S>

pub fn from_std(hash_map: StdHashMap<K, V, S>) -> Self

pub fn into_std(self) -> StdHashMap<K, V, S>

pub fn with_hasher(hash_builder: 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.

pub fn capacity(&self) -> usize

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.

pub fn keys(&self) -> Keys<'_, K, V>

An iterator visiting all keys in arbitrary order. The iterator element type is &'a K.

pub fn into_keys(self) -> IntoKeys<K, V>

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.

pub fn values(&self) -> Values<'_, K, V>

An iterator visiting all values in arbitrary order. The iterator element type is &'a V.

pub fn values_mut(&mut self) -> ValuesMut<'_, K, V>

An iterator visiting all values mutably in arbitrary order. The iterator element type is &'a mut V.

pub fn into_values(self) -> IntoValues<K, V>

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.

pub fn iter(&self) -> Iter<'_, K, V>

An iterator visiting all key-value pairs in arbitrary order. The iterator element type is (&'a K, &'a V).

pub fn iter_mut(&mut self) -> IterMut<'_, K, V>

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).

pub fn len(&self) -> usize

Returns the number of elements in the map.

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

pub fn drain(&mut self) -> Drain<'_, K, V>

Clears the map, returning all key-value pairs as an iterator. Keeps the allocated memory for reuse.

If the returned iterator is dropped before being fully consumed, it drops the remaining key-value pairs. The returned iterator keeps a mutable borrow on the vector to optimize its implementation.

pub fn retain<F>(&mut self, f: F)

where F: FnMut(&K, &mut V) -> bool,

Retains only the elements specified by the predicate.

In other words, remove all pairs (k, v) for which f(&k, &mut v) returns false. The elements are visited in unsorted (and unspecified) order.

pub fn clear(&mut self)

Clears the map, removing all key-value pairs. Keeps the allocated memory for reuse.

pub fn hasher(&self) -> &S

Returns a reference to the map’s BuildHasher.

impl<K, V, S> HashMap<K, V, S>

where K: Eq + Hash, S: BuildHasher,

pub fn try_with_capacity( capacity: usize, ) -> Result<HashMap<K, V, S>, AllocError>

where S: 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.

pub fn try_with_capacity_and_hasher( capacity: usize, hash_builder: S, ) -> Result<HashMap<K, V, S>, AllocError>

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.

pub fn try_reserve(&mut self, additional: usize) -> Result<(), AllocError>

Tries to reserve capacity for at least additional more elements to be inserted in the given HashMap<K, V>. The collection may reserve more space to avoid frequent reallocations.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

pub fn try_entry(&mut self, key: K) -> Result<Entry<'_, K, V>, AllocError>

Gets the given key’s corresponding entry in the map for in-place manipulation.

pub fn get<Q>(&self, k: &Q) -> Option<&V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

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.

pub fn get_key_value<Q>(&self, k: &Q) -> Option<(&K, &V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

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.

pub fn contains_key<Q>(&self, k: &Q) -> bool

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

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.

pub fn get_mut<Q>(&mut self, k: &Q) -> Option<&mut V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

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.

pub fn try_insert(&mut self, k: K, v: V) -> Result<Option<V>, AllocError>

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.

pub fn remove<Q>(&mut self, k: &Q) -> Option<V>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

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.

pub fn remove_entry<Q>(&mut self, k: &Q) -> Option<(K, V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

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.

Trait Implementations

impl<K, V, S> Debug for HashMap<K, V, S>

where K: Debug, V: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<K, V, S> Default for HashMap<K, V, S>

where S: Default,

fn default() -> Self

Returns the “default value” for a type.

impl<K, Q, V, S> Index<&Q> for HashMap<K, V, S>

where K: Eq + Hash + Borrow<Q>, Q: Eq + Hash + ?Sized, S: BuildHasher,

fn index(&self, key: &Q) -> &V

Returns a reference to the value corresponding to the supplied key.

Panics

Panics if the key is not present in the HashMap.

type Output = V

The returned type after indexing.

impl<'a, K, V, S> IntoIterator for &'a HashMap<K, V, S>

type Item = (&'a K, &'a V)

The type of the elements being iterated over.

type IntoIter = Iter<'a, K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Iter<'a, K, V>

Creates an iterator from a value.

impl<'a, K, V, S> IntoIterator for &'a mut HashMap<K, V, S>

type Item = (&'a K, &'a mut V)

The type of the elements being iterated over.

type IntoIter = IterMut<'a, K, V>

Which kind of iterator are we turning this into?

fn into_iter(self) -> IterMut<'a, K, V>

Creates an iterator from a value.

impl<K, V, S> IntoIterator for HashMap<K, V, S>

fn into_iter(self) -> 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.

type Item = (K, V)

The type of the elements being iterated over.

type IntoIter = IntoIter<K, V>

Which kind of iterator are we turning this into?

impl<K, V, S> PartialEq for HashMap<K, V, S>

where K: Eq + Hash, V: PartialEq, S: BuildHasher,

fn eq(&self, other: &HashMap<K, V, S>) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl<K, V, S> Eq for HashMap<K, V, S>

where K: Eq + Hash, V: Eq, S: BuildHasher,