Struct AxDashMap 

pub struct AxDashMap<K, V, S = BuildHasherDefault<AxHasher>>(/* private fields */);

Implementations

impl<K, V> AxDashMap<K, V, BuildHasherDefault<AxHasher>>

where K: Hash + Eq,

pub fn new() -> Self

Creates an empty map with the default AxHasher and the default shard count (number of shards = logical CPUs × 4, clamped to a power of two).

pub fn with_capacity(capacity: usize) -> Self

Creates an empty map pre-allocated for at least capacity entries, using the default AxHasher and the default shard count.

pub fn with_shard_amount(shard_amount: usize) -> Self

Creates an empty map with the default AxHasher and an explicit shard count. shard_amount must be a power of two; dashmap panics otherwise.

More shards → less lock contention under high concurrency. Fewer shards → lower memory overhead.

pub fn with_capacity_and_shard_amount( capacity: usize, shard_amount: usize, ) -> Self

Creates an empty map with the default AxHasher, a pre-allocated capacity, and an explicit shard count.

impl<K, V, S> AxDashMap<K, V, S>

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

pub fn with_hasher(hasher: S) -> Self

Creates an empty map using a custom BuildHasher.

Use this when you need a seeded hasher for hash-flooding resistance:

use axhash_dashmap::{AxDashMap, AxBuildHasher};

let seed: u64 = 0xdeadbeef_cafebabe;
let map: AxDashMap<String, u32, AxBuildHasher> =
    AxDashMap::with_hasher(AxBuildHasher::with_seed(seed));

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

Creates an empty map with at least capacity entries and a custom BuildHasher.

pub fn with_hasher_and_shard_amount(hasher: S, shard_amount: usize) -> Self

Creates an empty map with a custom BuildHasher and an explicit shard count.

pub fn with_capacity_and_hasher_and_shard_amount( capacity: usize, hasher: S, shard_amount: usize, ) -> Self

Creates an empty map with a pre-allocated capacity, a custom BuildHasher, and an explicit shard count.

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

Consumes the wrapper and returns the underlying RawDashMap.

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

pub fn hash_usize<T>(&self, item: &T) -> usize

where T: Hash,

Hash a given item to produce a usize. Uses the provided or default HashBuilder.

pub fn hasher(&self) -> &S

Returns a reference to the map’s BuildHasher.

Examples

use dashmap::DashMap;
use std::collections::hash_map::RandomState;

let hasher = RandomState::new();
let map: DashMap<i32, i32> = DashMap::new();
let hasher: &RandomState = map.hasher();

pub fn insert(&self, key: K, value: V) -> Option<V>

Inserts a key and a value into the map. Returns the old value associated with the key if there was one.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let map = DashMap::new();
map.insert("I am the key!", "And I am the value!");

pub fn remove<Q>(&self, key: &Q) -> Option<(K, V)>

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

Removes an entry from the map, returning the key and value if they existed in the map.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let soccer_team = DashMap::new();
soccer_team.insert("Jack", "Goalie");
assert_eq!(soccer_team.remove("Jack").unwrap().1, "Goalie");

pub fn remove_if<Q>( &self, key: &Q, f: impl FnOnce(&K, &V) -> bool, ) -> Option<(K, V)>

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

Removes an entry from the map, returning the key and value if the entry existed and the provided conditional function returned true.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

use dashmap::DashMap;

let soccer_team = DashMap::new();
soccer_team.insert("Sam", "Forward");
soccer_team.remove_if("Sam", |_, position| position == &"Goalie");
assert!(soccer_team.contains_key("Sam"));

use dashmap::DashMap;

let soccer_team = DashMap::new();
soccer_team.insert("Sam", "Forward");
soccer_team.remove_if("Sam", |_, position| position == &"Forward");
assert!(!soccer_team.contains_key("Sam"));

pub fn remove_if_mut<Q>( &self, key: &Q, f: impl FnOnce(&K, &mut V) -> bool, ) -> Option<(K, V)>

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

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

Creates an iterator over a DashMap yielding immutable references.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let words = DashMap::new();
words.insert("hello", "world");
assert_eq!(words.iter().count(), 1);

pub fn iter_mut(&'a self) -> IterMut<'a, K, V, S>

Iterator over a DashMap yielding mutable references.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let map = DashMap::new();
map.insert("Johnny", 21);
map.iter_mut().for_each(|mut r| *r += 1);
assert_eq!(*map.get("Johnny").unwrap(), 22);

pub fn get<Q>(&'a self, key: &Q) -> Option<Ref<'a, K, V>>

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

Get an immutable reference to an entry in the map

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let youtubers = DashMap::new();
youtubers.insert("Bosnian Bill", 457000);
assert_eq!(*youtubers.get("Bosnian Bill").unwrap(), 457000);

pub fn get_mut<Q>(&'a self, key: &Q) -> Option<RefMut<'a, K, V>>

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

Get a mutable reference to an entry in the map

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let class = DashMap::new();
class.insert("Albin", 15);
*class.get_mut("Albin").unwrap() -= 1;
assert_eq!(*class.get("Albin").unwrap(), 14);

pub fn try_get<Q>(&'a self, key: &Q) -> TryResult<Ref<'a, K, V>>

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

Get an immutable reference to an entry in the map, if the shard is not locked. If the shard is locked, the function will return TryResult::Locked.

Examples

use dashmap::DashMap;
use dashmap::try_result::TryResult;

let map = DashMap::new();
map.insert("Johnny", 21);

assert_eq!(*map.try_get("Johnny").unwrap(), 21);

let _result1_locking = map.get_mut("Johnny");

let result2 = map.try_get("Johnny");
assert!(result2.is_locked());

pub fn try_get_mut<Q>(&'a self, key: &Q) -> TryResult<RefMut<'a, K, V>>

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

Get a mutable reference to an entry in the map, if the shard is not locked. If the shard is locked, the function will return TryResult::Locked.

Examples

use dashmap::DashMap;
use dashmap::try_result::TryResult;

let map = DashMap::new();
map.insert("Johnny", 21);

*map.try_get_mut("Johnny").unwrap() += 1;
assert_eq!(*map.get("Johnny").unwrap(), 22);

let _result1_locking = map.get("Johnny");

let result2 = map.try_get_mut("Johnny");
assert!(result2.is_locked());

pub fn shrink_to_fit(&self)

Remove excess capacity to reduce memory usage.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;
use dashmap::try_result::TryResult;

let map = DashMap::new();
map.insert("Johnny", 21);
assert!(map.capacity() > 0);
map.remove("Johnny");
map.shrink_to_fit();
assert_eq!(map.capacity(), 0);

pub fn retain(&self, f: impl FnMut(&K, &mut V) -> bool)

Retain elements that whose predicates return true and discard elements whose predicates return false.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let people = DashMap::new();
people.insert("Albin", 15);
people.insert("Jones", 22);
people.insert("Charlie", 27);
people.retain(|_, v| *v > 20);
assert_eq!(people.len(), 2);

pub fn len(&self) -> usize

Fetches the total number of key-value pairs stored in the map.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let people = DashMap::new();
people.insert("Albin", 15);
people.insert("Jones", 22);
people.insert("Charlie", 27);
assert_eq!(people.len(), 3);

pub fn is_empty(&self) -> bool

Checks if the map is empty or not.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let map = DashMap::<(), ()>::new();
assert!(map.is_empty());

pub fn clear(&self)

Removes all key-value pairs in the map.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let stats = DashMap::new();
stats.insert("Goals", 4);
assert!(!stats.is_empty());
stats.clear();
assert!(stats.is_empty());

pub fn capacity(&self) -> usize

Returns how many key-value pairs the map can store without reallocating.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

pub fn alter<Q>(&self, key: &Q, f: impl FnOnce(&K, V) -> V)

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

Modify a specific value according to a function.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let stats = DashMap::new();
stats.insert("Goals", 4);
stats.alter("Goals", |_, v| v * 2);
assert_eq!(*stats.get("Goals").unwrap(), 8);

Panics

If the given closure panics, then alter will abort the process

pub fn alter_all(&self, f: impl FnMut(&K, V) -> V)

Modify every value in the map according to a function.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let stats = DashMap::new();
stats.insert("Wins", 4);
stats.insert("Losses", 2);
stats.alter_all(|_, v| v + 1);
assert_eq!(*stats.get("Wins").unwrap(), 5);
assert_eq!(*stats.get("Losses").unwrap(), 3);

Panics

If the given closure panics, then alter_all will abort the process

pub fn view<Q, R>(&self, key: &Q, f: impl FnOnce(&K, &V) -> R) -> Option<R>

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

Scoped access into an item of the map according to a function.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let warehouse = DashMap::new();
warehouse.insert(4267, ("Banana", 100));
warehouse.insert(2359, ("Pear", 120));
let fruit = warehouse.view(&4267, |_k, v| *v);
assert_eq!(fruit, Some(("Banana", 100)));

Panics

If the given closure panics, then view will abort the process

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

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

Checks if the map contains a specific key.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let team_sizes = DashMap::new();
team_sizes.insert("Dakota Cherries", 23);
assert!(team_sizes.contains_key("Dakota Cherries"));

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

Advanced entry API that tries to mimic std::collections::HashMap. See the documentation on dashmap::mapref::entry for more details.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

pub fn try_entry(&'a self, key: K) -> Option<Entry<'a, K, V>>

Advanced entry API that tries to mimic std::collections::HashMap. See the documentation on dashmap::mapref::entry for more details.

Returns None if the shard is currently locked.

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

Advanced entry API that tries to mimic std::collections::HashMap::try_reserve. Tries to reserve capacity for at least shard * additional and may reserve more space to avoid frequent reallocations.

Errors

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

Trait Implementations

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

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

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

Formats the value using the given formatter.

impl<K, V> Default for AxDashMap<K, V, BuildHasherDefault<AxHasher>>

where K: Hash + Eq,

fn default() -> Self

Returns the “default value” for a type.

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

type Target = DashMap<K, V, S>

The resulting type after dereferencing.

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

Dereferences the value.

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

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

Mutably dereferences the value.

impl<K, V, S> Extend<(K, V)> for AxDashMap<K, V, S>

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

fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, iter: I)

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

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

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

impl<K, V, S> From<AxDashMap<K, V, S>> for RawDashMap<K, V, S>

fn from(wrapper: AxDashMap<K, V, S>) -> Self

Converts to this type from the input type.

impl<K, V, S> From<DashMap<K, V, S>> for AxDashMap<K, V, S>

fn from(inner: RawDashMap<K, V, S>) -> Self

Converts to this type from the input type.

impl<K, V> FromIterator<(K, V)> for AxDashMap<K, V, BuildHasherDefault<AxHasher>>

where K: Hash + Eq,

fn from_iter<I: IntoIterator<Item = (K, V)>>(iter: I) -> Self

Creates a value from an iterator.