Struct HashMap

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

New-type for HashMap with FixedHasher as the default hashing provider. Can be trivially converted to and from a hashbrown HashMap using From.

A new-type is used instead of a type alias due to critical methods like new being incompatible with Bevy’s choice of default hasher.

Implementations

impl<K, V> HashMap<K, V, FixedHasher>

pub const fn new() -> Self

Creates an empty HashMap.

Refer to new for further details.

Examples

// Creates a HashMap with zero capacity.
let map = HashMap::new();

pub fn with_capacity(capacity: usize) -> Self

Creates an empty HashMap with the specified capacity.

Refer to with_capacity for further details.

Examples

// Creates a HashMap with capacity for at least 5 entries.
let map = HashMap::with_capacity(5);

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

pub const fn with_hasher(hash_builder: S) -> Self

Creates an empty HashMap which will use the given hash builder to hash keys.

Refer to with_hasher for further details.

Examples

// Creates a HashMap with the provided hasher.
let map = HashMap::with_hasher(SomeHasher);

pub fn with_capacity_and_hasher(capacity: usize, hash_builder: S) -> Self

Creates an empty HashMap with the specified capacity, using hash_builder to hash the keys.

Refer to with_capacity_and_hasher for further details.

Examples

// Creates a HashMap with capacity for 5 entries and the provided hasher.
let map = HashMap::with_capacity_and_hasher(5, SomeHasher);

pub fn hasher(&self) -> &S

Returns a reference to the map’s BuildHasher, or S parameter.

Refer to hasher for further details.

pub fn capacity(&self) -> usize

Returns the number of elements the map can hold without reallocating.

Refer to capacity for further details.

Examples

let map = HashMap::with_capacity(5);

assert!(map.capacity() >= 5);

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

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

Refer to keys for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for key in map.keys() {
    // foo, bar, baz
    // Note that the above order is not guaranteed
}

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

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

Refer to values for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for key in map.values() {
    // 0, 1, 2
    // Note that the above order is not guaranteed
}

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.

Refer to values for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for key in map.values_mut() {
    // 0, 1, 2
    // Note that the above order is not guaranteed
}

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).

Refer to iter for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for (key, value) in map.iter() {
    // ("foo", 0), ("bar", 1), ("baz", 2)
    // Note that the above order is not guaranteed
}

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).

Refer to iter_mut for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for (key, value) in map.iter_mut() {
    // ("foo", 0), ("bar", 1), ("baz", 2)
    // Note that the above order is not guaranteed
}

pub fn len(&self) -> usize

Returns the number of elements in the map.

Refer to len for further details.

Examples

let mut map = HashMap::new();

assert_eq!(map.len(), 0);

map.insert("foo", 0);

assert_eq!(map.len(), 1);

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

Refer to is_empty for further details.

Examples

let mut map = HashMap::new();

assert!(map.is_empty());

map.insert("foo", 0);

assert!(!map.is_empty());

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.

Refer to drain for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for (key, value) in map.drain() {
    // ("foo", 0), ("bar", 1), ("baz", 2)
    // Note that the above order is not guaranteed
}

assert!(map.is_empty());

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

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

Retains only the elements specified by the predicate. Keeps the allocated memory for reuse.

Refer to retain for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

map.retain(|key, value| *value == 2);

assert_eq!(map.len(), 1);

pub fn extract_if<F>(&mut self, f: F) -> ExtractIf<'_, K, V, F>

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

Drains elements which are true under the given predicate, and returns an iterator over the removed items.

Refer to extract_if for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

let extracted = map
    .extract_if(|key, value| *value == 2)
    .collect::<Vec<_>>();

assert_eq!(map.len(), 2);
assert_eq!(extracted.len(), 1);

pub fn clear(&mut self)

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

Refer to clear for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

map.clear();

assert!(map.is_empty());

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.

Refer to into_keys for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for key in map.into_keys() {
    // "foo", "bar", "baz"
    // Note that the above order is not guaranteed
}

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.

Refer to into_values for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

for key in map.into_values() {
    // 0, 1, 2
    // Note that the above order is not guaranteed
}

pub fn into_inner(self) -> HashMap<K, V, S>

Takes the inner HashMap out of this wrapper.

Examples

let map: HashMap<&'static str, usize> = HashMap::new();
let map: hashbrown::HashMap<&'static str, usize, _> = map.into_inner();

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

where K: Eq + Hash, S: BuildHasher,

pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more elements to be inserted in the HashMap. The collection may reserve more space to avoid frequent reallocations.

Refer to reserve for further details.

Examples

let mut map = HashMap::with_capacity(5);

assert!(map.capacity() >= 5);

map.reserve(10);

assert!(map.capacity() - map.len() >= 10);

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

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.

Refer to try_reserve for further details.

Examples

let mut map = HashMap::with_capacity(5);

assert!(map.capacity() >= 5);

map.try_reserve(10).expect("Out of Memory!");

assert!(map.capacity() - map.len() >= 10);

pub fn shrink_to_fit(&mut self)

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.

Refer to shrink_to_fit for further details.

Examples

let mut map = HashMap::with_capacity(5);

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

assert!(map.capacity() >= 5);

map.shrink_to_fit();

assert_eq!(map.capacity(), 3);

pub fn shrink_to(&mut self, min_capacity: usize)

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.

Refer to shrink_to for further details.

pub fn entry(&mut self, key: K) -> Entry<'_, K, V, S>

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

Refer to entry for further details.

Examples

let mut map = HashMap::new();

let value = map.entry("foo").or_insert(0);

pub fn entry_ref<'a, 'b, Q>( &'a mut self, key: &'b Q, ) -> EntryRef<'a, 'b, K, Q, V, S>

where Q: Hash + Equivalent<K> + ?Sized,

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

Refer to entry_ref for further details.

Examples

let mut map = HashMap::new();

let value = map.entry_ref("foo").or_insert(0);

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

where Q: Hash + Equivalent<K> + ?Sized,

Returns a reference to the value corresponding to the key.

Refer to get for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert_eq!(map.get("foo"), Some(&0));

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

where Q: Hash + Equivalent<K> + ?Sized,

Returns the key-value pair corresponding to the supplied key.

Refer to get_key_value for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert_eq!(map.get_key_value("foo"), Some((&"foo", &0)));

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

where Q: Hash + Equivalent<K> + ?Sized,

Returns the key-value pair corresponding to the supplied key, with a mutable reference to value.

Refer to get_key_value_mut for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert_eq!(map.get_key_value_mut("foo"), Some((&"foo", &mut 0)));

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

where Q: Hash + Equivalent<K> + ?Sized,

Returns true if the map contains a value for the specified key.

Refer to contains_key for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert!(map.contains_key("foo"));

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

where Q: Hash + Equivalent<K> + ?Sized,

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

Refer to get_mut for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert_eq!(map.get_mut("foo"), Some(&mut 0));

pub fn get_many_mut<Q, const N: usize>( &mut self, ks: [&Q; N], ) -> [Option<&mut V>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once.

Refer to get_many_mut for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

let result = map.get_many_mut(["foo", "bar"]);

assert_eq!(result, [Some(&mut 0), Some(&mut 1)]);

pub fn get_many_key_value_mut<Q, const N: usize>( &mut self, ks: [&Q; N], ) -> [Option<(&K, &mut V)>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once, with immutable references to the corresponding keys.

Refer to get_many_key_value_mut for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);
map.insert("bar", 1);
map.insert("baz", 2);

let result = map.get_many_key_value_mut(["foo", "bar"]);

assert_eq!(result, [Some((&"foo", &mut 0)), Some((&"bar", &mut 1))]);

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

Inserts a key-value pair into the map.

Refer to insert for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert_eq!(map.get("foo"), Some(&0));

pub fn try_insert( &mut self, key: K, value: V, ) -> Result<&mut V, OccupiedError<'_, K, V, S>>

Tries to insert a key-value pair into the map, and returns a mutable reference to the value in the entry.

Refer to try_insert for further details.

Examples

let mut map = HashMap::new();

map.try_insert("foo", 0).unwrap();

assert!(map.try_insert("foo", 1).is_err());

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

where Q: Hash + Equivalent<K> + ?Sized,

Removes a key from the map, returning the value at the key if the key was previously in the map. Keeps the allocated memory for reuse.

Refer to remove for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert_eq!(map.remove("foo"), Some(0));

assert!(map.is_empty());

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

where Q: Hash + Equivalent<K> + ?Sized,

Removes a key from the map, returning the stored key and value if the key was previously in the map. Keeps the allocated memory for reuse.

Refer to remove_entry for further details.

Examples

let mut map = HashMap::new();

map.insert("foo", 0);

assert_eq!(map.remove_entry("foo"), Some(("foo", 0)));

assert!(map.is_empty());

pub fn allocation_size(&self) -> usize

Returns the total amount of memory allocated internally by the hash set, in bytes.

Refer to allocation_size for further details.

Examples

let mut map = HashMap::new();

assert_eq!(map.allocation_size(), 0);

map.insert("foo", 0u32);

assert!(map.allocation_size() >= size_of::<&'static str>() + size_of::<u32>());

pub unsafe fn insert_unique_unchecked( &mut self, key: K, value: V, ) -> (&K, &mut V)

Insert a key-value pair into the map without checking if the key already exists in the map.

Refer to insert_unique_unchecked for further details.

Safety

This operation is safe if a key does not exist in the map.

However, if a key exists in the map already, the behavior is unspecified: this operation may panic, loop forever, or any following operation with the map may panic, loop forever or return arbitrary result.

That said, this operation (and following operations) are guaranteed to not violate memory safety.

However this operation is still unsafe because the resulting HashMap may be passed to unsafe code which does expect the map to behave correctly, and would cause unsoundness as a result.

pub unsafe fn get_many_unchecked_mut<Q, const N: usize>( &mut self, keys: [&Q; N], ) -> [Option<&mut V>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once, without validating that the values are unique.

Refer to get_many_unchecked_mut for further details.

Returns an array of length N with the results of each query. None will be used if the key is missing.

For a safe alternative see get_many_mut.

Safety

Calling this method with overlapping keys is undefined behavior even if the resulting references are not used.

pub unsafe fn get_many_key_value_unchecked_mut<Q, const N: usize>( &mut self, keys: [&Q; N], ) -> [Option<(&K, &mut V)>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once, with immutable references to the corresponding keys, without validating that the values are unique.

Refer to get_many_key_value_unchecked_mut for further details.

Returns an array of length N with the results of each query. None will be returned if any of the keys are missing.

For a safe alternative see get_many_key_value_mut.

Safety

Calling this method with overlapping keys is undefined behavior even if the resulting references are not used.

Methods from Deref<Target = HashMap<K, V, S>>

pub fn allocator(&self) -> &A

Returns a reference to the underlying allocator.

pub fn hasher(&self) -> &S

Returns a reference to the map’s BuildHasher.

Examples

use hashbrown::HashMap;
use hashbrown::DefaultHashBuilder;

let hasher = DefaultHashBuilder::default();
let map: HashMap<i32, i32> = HashMap::with_hasher(hasher);
let hasher: &DefaultHashBuilder = map.hasher();

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.

Examples

use hashbrown::HashMap;
let map: HashMap<i32, i32> = HashMap::with_capacity(100);
assert_eq!(map.len(), 0);
assert!(map.capacity() >= 100);

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

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

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
assert_eq!(map.len(), 3);
let mut vec: Vec<&str> = Vec::new();

for key in map.keys() {
    println!("{}", key);
    vec.push(*key);
}

// The `Keys` iterator produces keys in arbitrary order, so the
// keys must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, ["a", "b", "c"]);

assert_eq!(map.len(), 3);

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

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

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
assert_eq!(map.len(), 3);
let mut vec: Vec<i32> = Vec::new();

for val in map.values() {
    println!("{}", val);
    vec.push(*val);
}

// The `Values` iterator produces values in arbitrary order, so the
// values must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [1, 2, 3]);

assert_eq!(map.len(), 3);

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

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

Examples

use hashbrown::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;
}

assert_eq!(map.len(), 3);
let mut vec: Vec<i32> = Vec::new();

for val in map.values() {
    println!("{}", val);
    vec.push(*val);
}

// The `Values` iterator produces values in arbitrary order, so the
// values must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [11, 12, 13]);

assert_eq!(map.len(), 3);

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

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

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);
assert_eq!(map.len(), 3);
let mut vec: Vec<(&str, i32)> = Vec::new();

for (key, val) in map.iter() {
    println!("key: {} val: {}", key, val);
    vec.push((*key, *val));
}

// The `Iter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3)]);

assert_eq!(map.len(), 3);

pub fn iter_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).

Examples

use hashbrown::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;
}

assert_eq!(map.len(), 3);
let mut vec: Vec<(&str, i32)> = Vec::new();

for (key, val) in &map {
    println!("key: {} val: {}", key, val);
    vec.push((*key, *val));
}

// The `Iter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 2), ("b", 4), ("c", 6)]);

assert_eq!(map.len(), 3);

pub fn len(&self) -> usize

Returns the number of elements in the map.

Examples

use hashbrown::HashMap;

let mut a = HashMap::new();
assert_eq!(a.len(), 0);
a.insert(1, "a");
assert_eq!(a.len(), 1);

pub fn is_empty(&self) -> bool

Returns true if the map contains no elements.

Examples

use hashbrown::HashMap;

let mut a = HashMap::new();
assert!(a.is_empty());
a.insert(1, "a");
assert!(!a.is_empty());

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

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.

Examples

use hashbrown::HashMap;

let mut a = HashMap::new();
a.insert(1, "a");
a.insert(2, "b");
let capacity_before_drain = a.capacity();

for (k, v) in a.drain().take(1) {
    assert!(k == 1 || k == 2);
    assert!(v == "a" || v == "b");
}

// As we can see, the map is empty and contains no element.
assert!(a.is_empty() && a.len() == 0);
// But map capacity is equal to old one.
assert_eq!(a.capacity(), capacity_before_drain);

let mut a = HashMap::new();
a.insert(1, "a");
a.insert(2, "b");

{   // Iterator is dropped without being consumed.
    let d = a.drain();
}

// But the map is empty even if we do not use Drain iterator.
assert!(a.is_empty());

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

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

Retains only the elements specified by the predicate. Keeps the allocated memory for reuse.

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

Examples

use hashbrown::HashMap;

let mut map: HashMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
assert_eq!(map.len(), 8);

map.retain(|&k, _| k % 2 == 0);

// We can see, that the number of elements inside map is changed.
assert_eq!(map.len(), 4);

let mut vec: Vec<(i32, i32)> = map.iter().map(|(&k, &v)| (k, v)).collect();
vec.sort_unstable();
assert_eq!(vec, [(0, 0), (2, 20), (4, 40), (6, 60)]);

pub fn extract_if<F>(&mut self, f: F) -> ExtractIf<'_, K, V, F, A>

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

Drains elements which are true under the given predicate, and returns an iterator over the removed items.

In other words, move all pairs (k, v) such that f(&k, &mut v) returns true out into another iterator.

Note that extract_if lets you mutate every value in the filter closure, regardless of whether you choose to keep or remove it.

If the returned ExtractIf is not exhausted, e.g. because it is dropped without iterating or the iteration short-circuits, then the remaining elements will be retained. Use retain() with a negated predicate if you do not need the returned iterator.

Keeps the allocated memory for reuse.

Examples

use hashbrown::HashMap;

let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();

let drained: HashMap<i32, i32> = map.extract_if(|k, _v| k % 2 == 0).collect();

let mut evens = drained.keys().cloned().collect::<Vec<_>>();
let mut odds = map.keys().cloned().collect::<Vec<_>>();
evens.sort();
odds.sort();

assert_eq!(evens, vec![0, 2, 4, 6]);
assert_eq!(odds, vec![1, 3, 5, 7]);

let mut map: HashMap<i32, i32> = (0..8).map(|x| (x, x)).collect();

{   // Iterator is dropped without being consumed.
    let d = map.extract_if(|k, _v| k % 2 != 0);
}

// ExtractIf was not exhausted, therefore no elements were drained.
assert_eq!(map.len(), 8);

pub fn clear(&mut self)

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

Examples

use hashbrown::HashMap;

let mut a = HashMap::new();
a.insert(1, "a");
let capacity_before_clear = a.capacity();

a.clear();

// Map is empty.
assert!(a.is_empty());
// But map capacity is equal to old one.
assert_eq!(a.capacity(), capacity_before_clear);

pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more elements to be inserted in the HashMap. The collection may reserve more space to avoid frequent reallocations.

Panics

Panics if the new capacity exceeds isize::MAX bytes and abort the program in case of allocation error. Use try_reserve instead if you want to handle memory allocation failure.

Examples

use hashbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::new();
// Map is empty and doesn't allocate memory
assert_eq!(map.capacity(), 0);

map.reserve(10);

// And now map can hold at least 10 elements
assert!(map.capacity() >= 10);

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

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.

Examples

use hashbrown::HashMap;

let mut map: HashMap<&str, isize> = HashMap::new();
// Map is empty and doesn't allocate memory
assert_eq!(map.capacity(), 0);

map.try_reserve(10).expect("why is the test harness OOMing on 10 bytes?");

// And now map can hold at least 10 elements
assert!(map.capacity() >= 10);

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

use hashbrown::HashMap;
use hashbrown::TryReserveError;
let mut map: HashMap<i32, i32> = HashMap::new();

match map.try_reserve(usize::MAX) {
    Err(error) => match error {
        TryReserveError::CapacityOverflow => {}
        _ => panic!("TryReserveError::AllocError ?"),
    },
    _ => panic!(),
}

pub fn shrink_to_fit(&mut self)

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 hashbrown::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);

pub fn shrink_to(&mut self, min_capacity: usize)

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 hashbrown::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);

pub fn entry(&mut self, key: K) -> Entry<'_, K, V, S, A>

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

Examples

use hashbrown::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);

pub fn entry_ref<'a, 'b, Q>( &'a mut self, key: &'b Q, ) -> EntryRef<'a, 'b, K, Q, V, S, A>

where Q: Hash + Equivalent<K> + ?Sized,

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

Examples

use hashbrown::HashMap;

let mut words: HashMap<String, usize> = HashMap::new();
let source = ["poneyland", "horseyland", "poneyland", "poneyland"];
for (i, &s) in source.iter().enumerate() {
    let counter = words.entry_ref(s).or_insert(0);
    *counter += 1;
}

assert_eq!(words["poneyland"], 3);
assert_eq!(words["horseyland"], 1);

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

where Q: Hash + Equivalent<K> + ?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.

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.get(&1), Some(&"a"));
assert_eq!(map.get(&2), None);

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

where Q: Hash + Equivalent<K> + ?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.

Examples

use hashbrown::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);

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

where Q: Hash + Equivalent<K> + ?Sized,

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.

Examples

use hashbrown::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);

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

where Q: Hash + Equivalent<K> + ?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.

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
map.insert(1, "a");
assert_eq!(map.contains_key(&1), true);
assert_eq!(map.contains_key(&2), false);

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

where Q: Hash + Equivalent<K> + ?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.

Examples

use hashbrown::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");

assert_eq!(map.get_mut(&2), None);

pub fn get_many_mut<Q, const N: usize>( &mut self, ks: [&Q; N], ) -> [Option<&mut V>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once.

Returns an array of length N with the results of each query. For soundness, at most one mutable reference will be returned to any value. None will be used if the key is missing.

Panics

Panics if any keys are overlapping.

Examples

use hashbrown::HashMap;

let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);

// Get Athenæum and Bodleian Library
let [Some(a), Some(b)] = libraries.get_many_mut([
    "Athenæum",
    "Bodleian Library",
]) else { panic!() };

// Assert values of Athenæum and Library of Congress
let got = libraries.get_many_mut([
    "Athenæum",
    "Library of Congress",
]);
assert_eq!(
    got,
    [
        Some(&mut 1807),
        Some(&mut 1800),
    ],
);

// Missing keys result in None
let got = libraries.get_many_mut([
    "Athenæum",
    "New York Public Library",
]);
assert_eq!(
    got,
    [
        Some(&mut 1807),
        None
    ]
);

use hashbrown::HashMap;

let mut libraries = HashMap::new();
libraries.insert("Athenæum".to_string(), 1807);

// Duplicate keys panic!
let got = libraries.get_many_mut([
    "Athenæum",
    "Athenæum",
]);

pub unsafe fn get_many_unchecked_mut<Q, const N: usize>( &mut self, ks: [&Q; N], ) -> [Option<&mut V>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once, without validating that the values are unique.

Returns an array of length N with the results of each query. None will be used if the key is missing.

For a safe alternative see get_many_mut.

Safety

Calling this method with overlapping keys is undefined behavior even if the resulting references are not used.

Examples

use hashbrown::HashMap;

let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);

// SAFETY: The keys do not overlap.
let [Some(a), Some(b)] = (unsafe { libraries.get_many_unchecked_mut([
    "Athenæum",
    "Bodleian Library",
]) }) else { panic!() };

// SAFETY: The keys do not overlap.
let got = unsafe { libraries.get_many_unchecked_mut([
    "Athenæum",
    "Library of Congress",
]) };
assert_eq!(
    got,
    [
        Some(&mut 1807),
        Some(&mut 1800),
    ],
);

// SAFETY: The keys do not overlap.
let got = unsafe { libraries.get_many_unchecked_mut([
    "Athenæum",
    "New York Public Library",
]) };
// Missing keys result in None
assert_eq!(got, [Some(&mut 1807), None]);

pub fn get_many_key_value_mut<Q, const N: usize>( &mut self, ks: [&Q; N], ) -> [Option<(&K, &mut V)>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once, with immutable references to the corresponding keys.

Returns an array of length N with the results of each query. For soundness, at most one mutable reference will be returned to any value. None will be used if the key is missing.

Panics

Panics if any keys are overlapping.

Examples

use hashbrown::HashMap;

let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);

let got = libraries.get_many_key_value_mut([
    "Bodleian Library",
    "Herzogin-Anna-Amalia-Bibliothek",
]);
assert_eq!(
    got,
    [
        Some((&"Bodleian Library".to_string(), &mut 1602)),
        Some((&"Herzogin-Anna-Amalia-Bibliothek".to_string(), &mut 1691)),
    ],
);
// Missing keys result in None
let got = libraries.get_many_key_value_mut([
    "Bodleian Library",
    "Gewandhaus",
]);
assert_eq!(got, [Some((&"Bodleian Library".to_string(), &mut 1602)), None]);

use hashbrown::HashMap;

let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);

// Duplicate keys result in panic!
let got = libraries.get_many_key_value_mut([
    "Bodleian Library",
    "Herzogin-Anna-Amalia-Bibliothek",
    "Herzogin-Anna-Amalia-Bibliothek",
]);

pub unsafe fn get_many_key_value_unchecked_mut<Q, const N: usize>( &mut self, ks: [&Q; N], ) -> [Option<(&K, &mut V)>; N]

where Q: Hash + Equivalent<K> + ?Sized,

Attempts to get mutable references to N values in the map at once, with immutable references to the corresponding keys, without validating that the values are unique.

Returns an array of length N with the results of each query. None will be returned if any of the keys are missing.

For a safe alternative see get_many_key_value_mut.

Safety

Calling this method with overlapping keys is undefined behavior even if the resulting references are not used.

Examples

use hashbrown::HashMap;

let mut libraries = HashMap::new();
libraries.insert("Bodleian Library".to_string(), 1602);
libraries.insert("Athenæum".to_string(), 1807);
libraries.insert("Herzogin-Anna-Amalia-Bibliothek".to_string(), 1691);
libraries.insert("Library of Congress".to_string(), 1800);

let got = libraries.get_many_key_value_mut([
    "Bodleian Library",
    "Herzogin-Anna-Amalia-Bibliothek",
]);
assert_eq!(
    got,
    [
        Some((&"Bodleian Library".to_string(), &mut 1602)),
        Some((&"Herzogin-Anna-Amalia-Bibliothek".to_string(), &mut 1691)),
    ],
);
// Missing keys result in None
let got = libraries.get_many_key_value_mut([
    "Bodleian Library",
    "Gewandhaus",
]);
assert_eq!(
    got,
    [
        Some((&"Bodleian Library".to_string(), &mut 1602)),
        None,
    ],
);

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

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 std::collections module-level documentation for more.

Examples

use hashbrown::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");

pub unsafe fn insert_unique_unchecked(&mut self, k: K, v: V) -> (&K, &mut V)

Insert a key-value pair into the map without checking if the key already exists in the map.

This operation is faster than regular insert, because it does not perform lookup before insertion.

This operation is useful during initial population of the map. For example, when constructing a map from another map, we know that keys are unique.

Returns a reference to the key and value just inserted.

Safety

This operation is safe if a key does not exist in the map.

However, if a key exists in the map already, the behavior is unspecified: this operation may panic, loop forever, or any following operation with the map may panic, loop forever or return arbitrary result.

That said, this operation (and following operations) are guaranteed to not violate memory safety.

However this operation is still unsafe because the resulting HashMap may be passed to unsafe code which does expect the map to behave correctly, and would cause unsoundness as a result.

Examples

use hashbrown::HashMap;

let mut map1 = HashMap::new();
assert_eq!(map1.insert(1, "a"), None);
assert_eq!(map1.insert(2, "b"), None);
assert_eq!(map1.insert(3, "c"), None);
assert_eq!(map1.len(), 3);

let mut map2 = HashMap::new();

for (key, value) in map1.into_iter() {
    unsafe {
        map2.insert_unique_unchecked(key, value);
    }
}

let (key, value) = unsafe { map2.insert_unique_unchecked(4, "d") };
assert_eq!(key, &4);
assert_eq!(value, &mut "d");
*value = "e";

assert_eq!(map2[&1], "a");
assert_eq!(map2[&2], "b");
assert_eq!(map2[&3], "c");
assert_eq!(map2[&4], "e");
assert_eq!(map2.len(), 4);

pub fn try_insert( &mut self, key: K, value: V, ) -> Result<&mut V, OccupiedError<'_, K, V, S, A>>

Tries to insert a key-value pair into the map, and returns a mutable reference to the value in the entry.

Errors

If the map already had this key present, nothing is updated, and an error containing the occupied entry and the value is returned.

Examples

Basic usage:

use hashbrown::HashMap;
use hashbrown::hash_map::OccupiedError;

let mut map = HashMap::new();
assert_eq!(map.try_insert(37, "a").unwrap(), &"a");

match map.try_insert(37, "b") {
    Err(OccupiedError { entry, value }) => {
        assert_eq!(entry.key(), &37);
        assert_eq!(entry.get(), &"a");
        assert_eq!(value, "b");
    }
    _ => panic!()
}

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

where Q: Hash + Equivalent<K> + ?Sized,

Removes a key from the map, returning the value at the key if the key was previously in the map. Keeps the allocated memory for reuse.

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.

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
// The map is empty
assert!(map.is_empty() && map.capacity() == 0);

map.insert(1, "a");

assert_eq!(map.remove(&1), Some("a"));
assert_eq!(map.remove(&1), None);

// Now map holds none elements
assert!(map.is_empty());

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

where Q: Hash + Equivalent<K> + ?Sized,

Removes a key from the map, returning the stored key and value if the key was previously in the map. Keeps the allocated memory for reuse.

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.

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
// The map is empty
assert!(map.is_empty() && map.capacity() == 0);

map.insert(1, "a");

assert_eq!(map.remove_entry(&1), Some((1, "a")));
assert_eq!(map.remove(&1), None);

// Now map hold none elements
assert!(map.is_empty());

pub fn allocation_size(&self) -> usize

Returns the total amount of memory allocated internally by the hash set, in bytes.

The returned number is informational only. It is intended to be primarily used for memory profiling.

pub fn raw_entry_mut(&mut self) -> RawEntryBuilderMut<'_, K, V, S, A>

Creates a raw entry builder for the HashMap.

Raw entries provide the lowest level of control for searching and manipulating a map. They must be manually initialized with a hash and then manually searched. After this, insertions into a vacant entry still require an owned key to be provided.

Raw entries are useful for such exotic situations as:

• Hash memoization
• Deferring the creation of an owned key until it is known to be required
• Using a search key that doesn’t work with the Borrow trait
• Using custom comparison logic without newtype wrappers

Because raw entries provide much more low-level control, it’s much easier to put the HashMap into an inconsistent state which, while memory-safe, will cause the map to produce seemingly random results. Higher-level and more foolproof APIs like entry should be preferred when possible.

In particular, the hash used to initialized the raw entry must still be consistent with the hash of the key that is ultimately stored in the entry. This is because implementations of HashMap may need to recompute hashes when resizing, at which point only the keys are available.

Raw entries give mutable access to the keys. This must not be used to modify how the key would compare or hash, as the map will not re-evaluate where the key should go, meaning the keys may become “lost” if their location does not reflect their state. For instance, if you change a key so that the map now contains keys which compare equal, search may start acting erratically, with two keys randomly masking each other. Implementations are free to assume this doesn’t happen (within the limits of memory-safety).

Examples

use core::hash::{BuildHasher, Hash};
use hashbrown::hash_map::{HashMap, RawEntryMut};

let mut map = HashMap::new();
map.extend([("a", 100), ("b", 200), ("c", 300)]);

fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
    use core::hash::Hasher;
    let mut state = hash_builder.build_hasher();
    key.hash(&mut state);
    state.finish()
}

// Existing key (insert and update)
match map.raw_entry_mut().from_key(&"a") {
    RawEntryMut::Vacant(_) => unreachable!(),
    RawEntryMut::Occupied(mut view) => {
        assert_eq!(view.get(), &100);
        let v = view.get_mut();
        let new_v = (*v) * 10;
        *v = new_v;
        assert_eq!(view.insert(1111), 1000);
    }
}

assert_eq!(map[&"a"], 1111);
assert_eq!(map.len(), 3);

// Existing key (take)
let hash = compute_hash(map.hasher(), &"c");
match map.raw_entry_mut().from_key_hashed_nocheck(hash, &"c") {
    RawEntryMut::Vacant(_) => unreachable!(),
    RawEntryMut::Occupied(view) => {
        assert_eq!(view.remove_entry(), ("c", 300));
    }
}
assert_eq!(map.raw_entry().from_key(&"c"), None);
assert_eq!(map.len(), 2);

// Nonexistent key (insert and update)
let key = "d";
let hash = compute_hash(map.hasher(), &key);
match map.raw_entry_mut().from_hash(hash, |q| *q == key) {
    RawEntryMut::Occupied(_) => unreachable!(),
    RawEntryMut::Vacant(view) => {
        let (k, value) = view.insert("d", 4000);
        assert_eq!((*k, *value), ("d", 4000));
        *value = 40000;
    }
}
assert_eq!(map[&"d"], 40000);
assert_eq!(map.len(), 3);

match map.raw_entry_mut().from_hash(hash, |q| *q == key) {
    RawEntryMut::Vacant(_) => unreachable!(),
    RawEntryMut::Occupied(view) => {
        assert_eq!(view.remove_entry(), ("d", 40000));
    }
}
assert_eq!(map.get(&"d"), None);
assert_eq!(map.len(), 2);

pub fn raw_entry(&self) -> RawEntryBuilder<'_, K, V, S, A>

Creates a raw immutable entry builder for the HashMap.

Raw entries provide the lowest level of control for searching and manipulating a map. They must be manually initialized with a hash and then manually searched.

This is useful for

• Hash memoization
• Using a search key that doesn’t work with the Borrow trait
• Using custom comparison logic without newtype wrappers

Unless you are in such a situation, higher-level and more foolproof APIs like get should be preferred.

Immutable raw entries have very limited use; you might instead want raw_entry_mut.

Examples

use core::hash::{BuildHasher, Hash};
use hashbrown::HashMap;

let mut map = HashMap::new();
map.extend([("a", 100), ("b", 200), ("c", 300)]);

fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
    use core::hash::Hasher;
    let mut state = hash_builder.build_hasher();
    key.hash(&mut state);
    state.finish()
}

for k in ["a", "b", "c", "d", "e", "f"] {
    let hash = compute_hash(map.hasher(), k);
    let v = map.get(&k).cloned();
    let kv = v.as_ref().map(|v| (&k, v));

    println!("Key: {} and value: {:?}", k, v);

    assert_eq!(map.raw_entry().from_key(&k), kv);
    assert_eq!(map.raw_entry().from_hash(hash, |q| *q == k), kv);
    assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash, &k), kv);
}

Trait Implementations

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

where HashMap<K, V, S>: Clone,

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

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

where HashMap<K, V, S>: 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 HashMap<K, V, S>: Default,

fn default() -> Self

Returns the “default value” for a type.

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

type Target = HashMap<K, V, S>

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

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

fn deref_mut(&mut self) -> &mut Self::Target

Mutably dereferences the value.

impl<'de, K, V, S> Deserialize<'de> for HashMap<K, V, S>

where HashMap<K, V, S>: Deserialize<'de>,

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<K, V, S, T> Extend<T> for HashMap<K, V, S>

where HashMap<K, V, S>: Extend<T>,

fn extend<U: IntoIterator<Item = T>>(&mut self, iter: U)

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<K, V, const N: usize> From<[(K, V); N]> for HashMap<K, V, FixedHasher>

where K: Eq + Hash,

fn from(arr: [(K, V); N]) -> Self

Converts to this type from the input type.

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

fn from(value: HashMap<K, V, S>) -> Self

Converts to this type from the input type.

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

fn from(value: HashMap<K, V, S>) -> Self

Converts to this type from the input type.

impl<T, S> From<HashMap<T, (), S>> for HashSet<T, S>

fn from(value: HashMap<T, (), S>) -> Self

Converts to this type from the input type.

impl<K, V, S, T> FromIterator<T> for HashMap<K, V, S>

where HashMap<K, V, S>: FromIterator<T>,

fn from_iter<U: IntoIterator<Item = T>>(iter: U) -> Self

Creates a value from an iterator.

impl<K, V, S, T> Index<T> for HashMap<K, V, S>

where HashMap<K, V, S>: Index<T>,

type Output = <HashMap<K, V, S> as Index<T>>::Output

The returned type after indexing.

fn index(&self, index: T) -> &Self::Output

Performs the indexing (container[index]) operation.

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

where &'a HashMap<K, V, S>: IntoIterator,

type Item = <&'a HashMap<K, V, S> as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <&'a HashMap<K, V, S> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

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

where &'a mut HashMap<K, V, S>: IntoIterator,

type Item = <&'a mut HashMap<K, V, S> as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <&'a mut HashMap<K, V, S> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

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

where HashMap<K, V, S>: IntoIterator,

type Item = <HashMap<K, V, S> as IntoIterator>::Item

The type of the elements being iterated over.

type IntoIter = <HashMap<K, V, S> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

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

where HashMap<K, V, S>: PartialEq,

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

where HashMap<K, V, S>: Serialize,

fn serialize<T>(&self, serializer: T) -> Result<T::Ok, T::Error>

where T: Serializer,

Serialize this value into the given Serde serializer.

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

where HashMap<K, V, S>: Eq,