Struct HashMap

pub struct HashMap<'alloc, K, V>(/* private fields */);

A hash map without Drop, that uses FxHasher to hash keys, and stores data in arena allocator.

Just a thin wrapper around hashbrown::HashMap, which disables the Drop implementation.

All APIs are the same, except create a HashMap with either new_in or with_capacity_in.

No Drops

Objects allocated into Oxc memory arenas are never Dropped. Memory is released in bulk when the allocator is dropped, without dropping the individual objects in the arena.

Therefore, it would produce a memory leak if you allocated Drop types into the arena which own memory allocations outside the arena.

Static checks make this impossible to do. HashMap::new_in and all other methods which create a HashMap will refuse to compile if either key or value is a Drop type.

Implementations

impl<'alloc, K, V> HashMap<'alloc, K, V>

pub fn new_in(allocator: &'alloc Allocator) -> Self

Creates an empty HashMap. 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.

pub fn with_capacity_in(capacity: usize, allocator: &'alloc Allocator) -> Self

Creates an empty HashMap with the specified capacity. 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.

pub fn into_keys(self) -> IntoKeys<K, V, &'alloc Bump>

Creates a consuming iterator visiting all the keys in arbitrary order.

The map cannot be used after calling this. The iterator element type is K.

pub fn into_values(self) -> IntoValues<K, V, &'alloc Bump>

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.

Methods from Deref<Target = HashMap<K, V, FxBuildHasher, &'alloc Bump>>

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.

Trait Implementations

impl<'alloc, K, V> Deref for HashMap<'alloc, K, V>

type Target = HashMap<K, V, FxBuildHasher, &'alloc Bump>

The resulting type after dereferencing.

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

Dereferences the value.

impl<'alloc, K, V> DerefMut for HashMap<'alloc, K, V>

fn deref_mut(&mut self) -> &mut HashMap<K, V, FxBuildHasher, &'alloc Bump>

Mutably dereferences the value.

impl<'alloc, 'i, K, V> IntoIterator for &'i HashMap<'alloc, K, V>

fn into_iter(self) -> Self::IntoIter

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.

type IntoIter = <&'i HashMap<K, V, FxBuildHasher, &'alloc Bump> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

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

The type of the elements being iterated over.

impl<'alloc, 'i, K, V> IntoIterator for &'i mut HashMap<'alloc, K, V>

fn into_iter(self) -> Self::IntoIter

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.

type IntoIter = <&'i mut HashMap<K, V, FxBuildHasher, &'alloc Bump> as IntoIterator>::IntoIter

Which kind of iterator are we turning this into?

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

The type of the elements being iterated over.

impl<'alloc, K, V> IntoIterator for HashMap<'alloc, K, V>

fn into_iter(self) -> Self::IntoIter

Creates a consuming iterator, that is, one that moves each key-value pair out of the map in arbitrary order.

The map cannot be used after calling this.

type IntoIter = IntoIter<K, V, &'alloc Bump>

Which kind of iterator are we turning this into?

type Item = (K, V)

The type of the elements being iterated over.

impl<K, V> PartialEq for HashMap<'_, K, V>

where K: Eq + Hash, V: 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> Eq for HashMap<'_, K, V>

where K: Eq + Hash, V: Eq,

impl<K, V> Send for HashMap<'_, K, V>

SAFETY: Not actually safe, but for enabling Send for downstream crates.

impl<K, V> Sync for HashMap<'_, K, V>

SAFETY: Not actually safe, but for enabling Sync for downstream crates.