Struct HashMap

pub struct HashMap<K, V, S = RandomState, A = Global>
where
    A: Allocator,
{ /* private fields */ }

Available on crate features dep_hashbrown and alloc only.

A hash map implemented with quadratic probing and SIMD lookup.

The default hashing algorithm is currently foldhash, 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:

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 hashbrown::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, which allows for more complex methods of getting, setting, updating and removing keys and their values:

use hashbrown::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.

use hashbrown::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 hashbrown::HashMap;

let timber_resources: HashMap<&str, i32> = [("Norway", 100), ("Denmark", 50), ("Iceland", 10)]
    .into_iter().collect();
// use the values stored in map

Implementations

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

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

Available on crate features dep_hashbrown or std only.

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.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap, for example with with_hasher method.

Examples

use hashbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::new();
assert_eq!(map.len(), 0);
assert_eq!(map.capacity(), 0);

pub fn with_capacity(capacity: usize) -> HashMap<K, V>

Available on crate features dep_hashbrown or std only.

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.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap, for example with with_capacity_and_hasher method.

Examples

use hashbrown::HashMap;
let mut map: HashMap<&str, i32> = HashMap::with_capacity(10);
assert_eq!(map.len(), 0);
assert!(map.capacity() >= 10);

impl<K, V, A> HashMap<K, V, RandomState, A>

where A: Allocator,

pub fn new_in(alloc: A) -> HashMap<K, V, RandomState, A>

Available on crate features dep_hashbrown or std only.

Creates an empty HashMap using the given allocator.

The hash map is initially created with a capacity of 0, so it will not allocate until it is first inserted into.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap, for example with with_hasher_in method.

Examples

use hashbrown::HashMap;
use bumpalo::Bump;

let bump = Bump::new();
let mut map = HashMap::new_in(&bump);

// The created HashMap holds none elements
assert_eq!(map.len(), 0);

// The created HashMap also doesn't allocate memory
assert_eq!(map.capacity(), 0);

// Now we insert element inside created HashMap
map.insert("One", 1);
// We can see that the HashMap holds 1 element
assert_eq!(map.len(), 1);
// And it also allocates some capacity
assert!(map.capacity() > 1);

pub fn with_capacity_in( capacity: usize, alloc: A, ) -> HashMap<K, V, RandomState, A>

Available on crate features dep_hashbrown or std only.

Creates an empty HashMap with the specified capacity using the given allocator.

The hash map will be able to hold at least capacity elements without reallocating. If capacity is 0, the hash map will not allocate.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap, for example with with_capacity_and_hasher_in method.

Examples

use hashbrown::HashMap;
use bumpalo::Bump;

let bump = Bump::new();
let mut map = HashMap::with_capacity_in(5, &bump);

// The created HashMap holds none elements
assert_eq!(map.len(), 0);
// But it can hold at least 5 elements without reallocating
let empty_map_capacity = map.capacity();
assert!(empty_map_capacity >= 5);

// Now we insert some 5 elements inside created HashMap
map.insert("One",   1);
map.insert("Two",   2);
map.insert("Three", 3);
map.insert("Four",  4);
map.insert("Five",  5);

// We can see that the HashMap holds 5 elements
assert_eq!(map.len(), 5);
// But its capacity isn't changed
assert_eq!(map.capacity(), empty_map_capacity)

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

pub const fn with_hasher(hash_builder: S) -> HashMap<K, V, S>

Available on crate features dep_hashbrown or std only.

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

The hash map is initially created with a capacity of 0, so it will not allocate until it is first inserted into.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap.

The hash_builder passed should implement the BuildHasher trait for the HashMap to be useful, see its documentation for details.

Examples

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

let s = DefaultHashBuilder::default();
let mut map = HashMap::with_hasher(s);
assert_eq!(map.len(), 0);
assert_eq!(map.capacity(), 0);

map.insert(1, 2);

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

Available on crate features dep_hashbrown or std only.

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.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap.

The hash_builder passed should implement the BuildHasher trait for the HashMap to be useful, see its documentation for details.

Examples

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

let s = DefaultHashBuilder::default();
let mut map = HashMap::with_capacity_and_hasher(10, s);
assert_eq!(map.len(), 0);
assert!(map.capacity() >= 10);

map.insert(1, 2);

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

where A: Allocator,

pub fn allocator(&self) -> &A

Available on crate features dep_hashbrown or std only.

Returns a reference to the underlying allocator.

pub const fn with_hasher_in(hash_builder: S, alloc: A) -> HashMap<K, V, S, A>

Available on crate features dep_hashbrown or std only.

Creates an empty HashMap which will use the given hash builder to hash keys. It will be allocated with the given allocator.

The hash map is initially created with a capacity of 0, so it will not allocate until it is first inserted into.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap.

Examples

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

let s = DefaultHashBuilder::default();
let mut map = HashMap::with_hasher(s);
map.insert(1, 2);

pub fn with_capacity_and_hasher_in( capacity: usize, hash_builder: S, alloc: A, ) -> HashMap<K, V, S, A>

Available on crate features dep_hashbrown or std only.

Creates an empty HashMap with the specified capacity, using hash_builder to hash the keys. It will be allocated with the given allocator.

The hash map will be able to hold at least capacity elements without reallocating. If capacity is 0, the hash map will not allocate.

HashDoS resistance

The hash_builder normally use a fixed key by default and that does not allow the HashMap to be protected against attacks such as HashDoS. Users who require HashDoS resistance should explicitly use std::collections::hash_map::RandomState as the hasher when creating a HashMap.

Examples

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

let s = DefaultHashBuilder::default();
let mut map = HashMap::with_capacity_and_hasher(10, s);
map.insert(1, 2);

pub fn hasher(&self) -> &S

Available on crate features dep_hashbrown or std only.

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

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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

Available on crate features dep_hashbrown or std only.

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

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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)

Available on crate features dep_hashbrown or std only.

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 into_keys(self) -> IntoKeys<K, V, A>

Available on crate features dep_hashbrown or std only.

Creates a consuming iterator visiting all the keys in arbitrary order. The map cannot be used after calling this. The iterator element type is K.

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

let mut vec: Vec<&str> = map.into_keys().collect();

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

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

Available on crate features dep_hashbrown or std only.

Creates a consuming iterator visiting all the values in arbitrary order. The map cannot be used after calling this. The iterator element type is V.

Examples

use hashbrown::HashMap;

let mut map = HashMap::new();
map.insert("a", 1);
map.insert("b", 2);
map.insert("c", 3);

let mut vec: Vec<i32> = map.into_values().collect();

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

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

where K: Eq + Hash, S: BuildHasher, A: Allocator,

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

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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)

Available on crate features dep_hashbrown or std only.

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)

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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)

Available on crate features dep_hashbrown or std only.

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>>

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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,

Available on crate features dep_hashbrown or std only.

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

Available on crate features dep_hashbrown or std only.

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.

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

where A: Allocator,

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

Available on crate features dep_hashbrown or std only.

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>

Available on crate features dep_hashbrown or std only.

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> Archive for HashMap<K, V, S>

where V: Archive, K: Archive + Hash + Eq, <K as Archive>::Archived: Hash + Eq,

type Archived = ArchivedHashMap<<K as Archive>::Archived, <V as Archive>::Archived>

The archived representation of this type.

type Resolver = HashMapResolver

The resolver for this type. It must contain all the additional information from serializing needed to make the archived type from the normal type.

fn resolve( &self, resolver: <HashMap<K, V, S> as Archive>::Resolver, out: Place<<HashMap<K, V, S> as Archive>::Archived>, )

Creates the archived version of this value at the given position and writes it to the given output.

const COPY_OPTIMIZATION: CopyOptimization<Self> = _

An optimization flag that allows the bytes of this type to be copied directly to a writer instead of calling serialize.

impl<A, B, K, V, H> ArchiveWith<HashMap<K, V, H>> for MapKV<A, B>

where A: ArchiveWith<K>, B: ArchiveWith<V>, H: Default + BuildHasher,

type Archived = ArchivedHashMap<<A as ArchiveWith<K>>::Archived, <B as ArchiveWith<V>>::Archived>

The archived type of Self with F.

type Resolver = HashMapResolver

The resolver of a Self with F.

fn resolve_with( field: &HashMap<K, V, H>, resolver: <MapKV<A, B> as ArchiveWith<HashMap<K, V, H>>>::Resolver, out: Place<<MapKV<A, B> as ArchiveWith<HashMap<K, V, H>>>::Archived>, )

Resolves the archived type using a reference to the field type F.

impl<K, V> BitSized<{$PTR_BITS * 3}> for HashMap<K, V>

const BIT_SIZE: usize = _

The bit size of this type (only the relevant data part, without padding).

const MIN_BYTE_SIZE: usize = _

The rounded up byte size for this type.

fn bit_size(&self) -> usize

Returns the bit size of this type (only the relevant data part, without padding).

fn min_byte_size(&self) -> usize

Returns the rounded up byte size for this type.

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

where K: Clone, V: Clone, S: Clone, A: Allocator + Clone,

fn clone(&self) -> HashMap<K, V, S, A>

Returns a copy of the value.

fn clone_from(&mut self, source: &HashMap<K, V, S, A>)

Performs copy-assignment from source.

impl<K, V> DataCollection for HashMap<K, V>

fn collection_capacity(&self) -> Result<usize, NotAvailable>

Returns [NotSupported][E::NotSupported].

fn collection_is_full(&self) -> Result<bool, NotAvailable>

Returns [NotSupported][E::NotSupported].

type Element = V

The element type of the collection.

fn collection_len(&self) -> Result<usize, NotAvailable>

Returns the current number of elements in the collection.

fn collection_is_empty(&self) -> Result<bool, NotAvailable>

Returns true if the collection is empty, false if it’s not.

fn collection_contains( &self, element: Self::Element, ) -> Result<bool, NotAvailable>

where V: PartialEq,

Returns true if the collection contains the given element.

fn collection_count( &self, element: &Self::Element, ) -> Result<usize, NotAvailable>

where V: PartialEq,

Counts the number of times a given element appears in the collection.

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

where K: Debug, V: Debug, A: Allocator,

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

Formats the value using the given formatter.

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

where S: Default, A: Default + Allocator,

fn default() -> HashMap<K, V, S, A>

Creates an empty HashMap<K, V, S, A>, with the Default value for the hasher and allocator.

Examples

use hashbrown::HashMap;
use std::collections::hash_map::RandomState;

// You can specify all types of HashMap, including hasher and allocator.
// Created map is empty and don't allocate memory
let map: HashMap<u32, String> = Default::default();
assert_eq!(map.capacity(), 0);
let map: HashMap<u32, String, RandomState> = HashMap::default();
assert_eq!(map.capacity(), 0);

impl<K, V, D, S> Deserialize<HashMap<K, V, S>, D> for ArchivedHashMap<<K as Archive>::Archived, <V as Archive>::Archived>

where K: Archive + Hash + Eq, <K as Archive>::Archived: Deserialize<K, D> + Hash + Eq, V: Archive, <V as Archive>::Archived: Deserialize<V, D>, D: Fallible + ?Sized, S: Default + BuildHasher,

fn deserialize( &self, deserializer: &mut D, ) -> Result<HashMap<K, V, S>, <D as Fallible>::Error>

Deserializes using the given deserializer

impl<A, B, K, V, D, S> DeserializeWith<ArchivedHashMap<<A as ArchiveWith<K>>::Archived, <B as ArchiveWith<V>>::Archived>, HashMap<K, V, S>, D> for MapKV<A, B>

where A: ArchiveWith<K> + DeserializeWith<<A as ArchiveWith<K>>::Archived, K, D>, B: ArchiveWith<V> + DeserializeWith<<B as ArchiveWith<V>>::Archived, V, D>, K: Ord + Hash + Eq, D: Fallible + ?Sized, S: Default + BuildHasher,

fn deserialize_with( field: &ArchivedHashMap<<A as ArchiveWith<K>>::Archived, <B as ArchiveWith<V>>::Archived>, deserializer: &mut D, ) -> Result<HashMap<K, V, S>, <D as Fallible>::Error>

Deserializes the field type F using the given deserializer.

impl<'a, K, V, S, A> Extend<&'a (K, V)> for HashMap<K, V, S, A>

where K: Eq + Hash + Copy, V: Copy, S: BuildHasher, A: Allocator,

Inserts all new key-values from the iterator and replaces values with existing keys with new values returned from the iterator.

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = &'a (K, V)>,

Inserts all new key-values from the iterator to existing HashMap<K, V, S, A>. Replace values with existing keys with new values returned from the iterator. The keys and values must implement Copy trait.

Examples

use hashbrown::hash_map::HashMap;

let mut map = HashMap::new();
map.insert(1, 100);

let arr = [(1, 1), (2, 2)];
let some_iter = arr.iter();
map.extend(some_iter);
// Replace values with existing keys with new values returned from the iterator.
// So that the map.get(&1) doesn't return Some(&100).
assert_eq!(map.get(&1), Some(&1));

let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
map.extend(&some_vec);

let some_arr = [(5, 5), (6, 6)];
map.extend(&some_arr);

let mut vec: Vec<_> = map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);

fn extend_one(&mut self, _: &'a (K, V))

🔬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<'a, K, V, S, A> Extend<(&'a K, &'a V)> for HashMap<K, V, S, A>

where K: Eq + Hash + Copy, V: Copy, S: BuildHasher, A: Allocator,

Inserts all new key-values from the iterator and replaces values with existing keys with new values returned from the iterator.

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = (&'a K, &'a V)>,

Inserts all new key-values from the iterator to existing HashMap<K, V, S, A>. Replace values with existing keys with new values returned from the iterator. The keys and values must implement Copy trait.

Examples

use hashbrown::hash_map::HashMap;

let mut map = HashMap::new();
map.insert(1, 100);

let arr = [(1, 1), (2, 2)];
let some_iter = arr.iter().map(|(k, v)| (k, v));
map.extend(some_iter);
// Replace values with existing keys with new values returned from the iterator.
// So that the map.get(&1) doesn't return Some(&100).
assert_eq!(map.get(&1), Some(&1));

let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
map.extend(some_vec.iter().map(|(k, v)| (k, v)));

let some_arr = [(5, 5), (6, 6)];
map.extend(some_arr.iter().map(|(k, v)| (k, v)));

// You can also extend from another HashMap
let mut new_map = HashMap::new();
new_map.extend(&map);
assert_eq!(new_map, map);

let mut vec: Vec<_> = new_map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);

fn extend_one(&mut self, _: (&'a K, &'a V))

🔬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, S, A> Extend<(K, V)> for HashMap<K, V, S, A>

where K: Eq + Hash, S: BuildHasher, A: Allocator,

Inserts all new key-values from the iterator and replaces values with existing keys with new values returned from the iterator.

fn extend<T>(&mut self, iter: T)

where T: IntoIterator<Item = (K, V)>,

Inserts all new key-values from the iterator to existing HashMap<K, V, S, A>. Replace values with existing keys with new values returned from the iterator.

Examples

use hashbrown::hash_map::HashMap;

let mut map = HashMap::new();
map.insert(1, 100);

let some_iter = [(1, 1), (2, 2)].into_iter();
map.extend(some_iter);
// Replace values with existing keys with new values returned from the iterator.
// So that the map.get(&1) doesn't return Some(&100).
assert_eq!(map.get(&1), Some(&1));

let some_vec: Vec<_> = vec![(3, 3), (4, 4)];
map.extend(some_vec);

let some_arr = [(5, 5), (6, 6)];
map.extend(some_arr);
let old_map_len = map.len();

// You can also extend from another HashMap
let mut new_map = HashMap::new();
new_map.extend(map);
assert_eq!(new_map.len(), old_map_len);

let mut vec: Vec<_> = new_map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so the
// items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [(1, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)]);

fn extend_one(&mut self, _: (K, V))

🔬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, A, const N: usize> From<[(K, V); N]> for HashMap<K, V, RandomState, A>

where K: Eq + Hash, A: Default + Allocator,

fn from(arr: [(K, V); N]) -> HashMap<K, V, RandomState, A>

Examples

use hashbrown::HashMap;

let map1 = HashMap::from([(1, 2), (3, 4)]);
let map2: HashMap<_, _> = [(1, 2), (3, 4)].into();
assert_eq!(map1, map2);

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

where A: Allocator,

fn from(map: HashMap<T, (), S, A>) -> HashSet<T, S, A>

Converts to this type from the input type.

impl<K, V, S, A> FromIterator<(K, V)> for HashMap<K, V, S, A>

where K: Eq + Hash, S: BuildHasher + Default, A: Default + Allocator,

fn from_iter<T>(iter: T) -> HashMap<K, V, S, A>

where T: IntoIterator<Item = (K, V)>,

Creates a value from an iterator.

impl<'py, K, V, S> FromPyObject<'py> for HashMap<K, V, S>

where K: FromPyObject<'py> + Eq + Hash, V: FromPyObject<'py>, S: BuildHasher + Default,

fn extract_bound(ob: &Bound<'py, PyAny>) -> Result<HashMap<K, V, S>, PyErr>

Extracts Self from the bound smart pointer obj.

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

where K: Eq + Hash, Q: Hash + Equivalent<K> + ?Sized, S: BuildHasher, A: Allocator,

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.

Examples

use hashbrown::HashMap;

let map: HashMap<_, _> = [("a", "One"), ("b", "Two")].into();

assert_eq!(map[&"a"], "One");
assert_eq!(map[&"b"], "Two");

type Output = V

The returned type after indexing.

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

where A: Allocator,

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

Creates an iterator over the entries of a HashMap in arbitrary order. The iterator element type is (&'a K, &'a V).

Return the same Iter struct as by the iter method on HashMap.

Examples

use hashbrown::HashMap;
let map_one: HashMap<_, _> = [(1, "a"), (2, "b"), (3, "c")].into();
let mut map_two = HashMap::new();

for (key, value) in &map_one {
    println!("Key: {}, Value: {}", key, value);
    map_two.insert(*key, *value);
}

assert_eq!(map_one, map_two);

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?

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

where A: Allocator,

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

Creates an iterator over the entries of a HashMap in arbitrary order with mutable references to the values. The iterator element type is (&'a K, &'a mut V).

Return the same IterMut struct as by the iter_mut method on HashMap.

Examples

use hashbrown::HashMap;
let mut map: HashMap<_, _> = [("a", 1), ("b", 2), ("c", 3)].into();

for (key, value) in &mut map {
    println!("Key: {}, Value: {}", key, value);
    *value *= 2;
}

let mut vec = map.iter().collect::<Vec<_>>();
// 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)]);

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?

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

where A: Allocator,

fn into_iter(self) -> IntoIter<K, V, A>

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 hashbrown::HashMap;

let map: HashMap<_, _> = [("a", 1), ("b", 2), ("c", 3)].into();

// Not possible with .iter()
let mut vec: Vec<(&str, i32)> = map.into_iter().collect();
// The `IntoIter` iterator produces items in arbitrary order, so
// the items must be sorted to test them against a sorted array.
vec.sort_unstable();
assert_eq!(vec, [("a", 1), ("b", 2), ("c", 3)]);

type Item = (K, V)

The type of the elements being iterated over.

type IntoIter = IntoIter<K, V, A>

Which kind of iterator are we turning this into?

impl<K, V, H> IntoPy<Py<PyAny>> for HashMap<K, V, H>

where K: Hash + Eq + IntoPy<Py<PyAny>>, V: IntoPy<Py<PyAny>>, H: BuildHasher,

fn into_py(self, py: Python<'_>) -> Py<PyAny>

👎Deprecated since 0.23.0: IntoPy is going to be replaced by IntoPyObject. See the migration guide (https://pyo3.rs/v0.23.0/migration) for more information.

Performs the conversion.

impl<'a, 'py, K, V, H> IntoPyObject<'py> for &'a HashMap<K, V, H>

where &'a K: IntoPyObject<'py> + Eq + Hash, &'a V: IntoPyObject<'py>, H: BuildHasher,

type Target = PyDict

The Python output type

type Output = Bound<'py, <&'a HashMap<K, V, H> as IntoPyObject<'py>>::Target>

The smart pointer type to use.

type Error = PyErr

The type returned in the event of a conversion error.

fn into_pyobject( self, py: Python<'py>, ) -> Result<<&'a HashMap<K, V, H> as IntoPyObject<'py>>::Output, <&'a HashMap<K, V, H> as IntoPyObject<'py>>::Error>

Performs the conversion.

impl<'py, K, V, H> IntoPyObject<'py> for HashMap<K, V, H>

where K: IntoPyObject<'py> + Eq + Hash, V: IntoPyObject<'py>, H: BuildHasher,

type Target = PyDict

The Python output type

type Output = Bound<'py, <HashMap<K, V, H> as IntoPyObject<'py>>::Target>

The smart pointer type to use.

type Error = PyErr

The type returned in the event of a conversion error.

fn into_pyobject( self, py: Python<'py>, ) -> Result<<HashMap<K, V, H> as IntoPyObject<'py>>::Output, <HashMap<K, V, H> as IntoPyObject<'py>>::Error>

Performs the conversion.

impl<K, V, AK, AV, S> PartialEq<HashMap<K, V, S>> for ArchivedHashMap<AK, AV>

where K: Hash + Eq + Borrow<AK>, AK: Hash + Eq, AV: PartialEq<V>, 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, A> PartialEq for HashMap<K, V, S, A>

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

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

where K: Serialize<S> + Hash + Eq, <K as Archive>::Archived: Hash + Eq, V: Serialize<S>, S: Fallible + Writer + Allocator + ?Sized, <S as Fallible>::Error: Source,

fn serialize( &self, serializer: &mut S, ) -> Result<<HashMap<K, V, RandomState> as Archive>::Resolver, <S as Fallible>::Error>

Writes the dependencies for the object and returns a resolver that can create the archived type.

impl<A, B, K, V, H, S> SerializeWith<HashMap<K, V, H>, S> for MapKV<A, B>

where A: ArchiveWith<K> + SerializeWith<K, S>, B: ArchiveWith<V> + SerializeWith<V, S>, K: Hash + Eq, <A as ArchiveWith<K>>::Archived: Eq + Hash, S: Fallible + Writer + Allocator + ?Sized, <S as Fallible>::Error: Source, H: Default + BuildHasher, <H as BuildHasher>::Hasher: Default,

fn serialize_with( field: &HashMap<K, V, H>, serializer: &mut S, ) -> Result<<MapKV<A, B> as ArchiveWith<HashMap<K, V, H>>>::Resolver, <S as Fallible>::Error>

Serializes the field type F using the given serializer.

impl<K, V, H> ToPyObject for HashMap<K, V, H>

where K: Hash + Eq + ToPyObject, V: ToPyObject, H: BuildHasher,

fn to_object(&self, py: Python<'_>) -> Py<PyAny>

👎Deprecated since 0.23.0: ToPyObject is going to be replaced by IntoPyObject. See the migration guide (https://pyo3.rs/v0.23.0/migration) for more information.

Converts self into a Python object.

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

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