pub struct RandomState {
    pub(crate) k0: u64,
    pub(crate) k1: u64,
    pub(crate) k2: u64,
    pub(crate) k3: u64,
Expand description

Provides a Hasher factory. This is typically used (e.g. by HashMap) to create AHashers in order to hash the keys of the map. See build_hasher below.

There are multiple constructors each is documented in more detail below:

ConstructorDynamically random?Seed
newEach instance uniqueRandomSource
generate_withEach instance uniqueu64 x 4 + RandomSource
with_seedFixed per processu64 + static random number
with_seedsFixedu64 x 4


§k0: u64§k1: u64§k2: u64§k3: u64



impl RandomState


pub fn new() -> RandomState

Create a new RandomState BuildHasher using random keys.

Each instance will have a unique set of keys derived from RandomSource.


pub fn generate_with(k0: u64, k1: u64, k2: u64, k3: u64) -> RandomState

Create a new RandomState BuildHasher based on the provided seeds, but in such a way that each time it is called the resulting state will be different and of high quality. This allows fixed constant or poor quality seeds to be provided without the problem of different BuildHashers being identical or weak.

This is done via permuting the provided values with the value of a static counter and memory address. (This makes this method somewhat more expensive than with_seeds below which does not do this).

The provided values (k0-k3) do not need to be of high quality but they should not all be the same value.


fn from_keys(a: &[u64; 4], b: &[u64; 4], c: usize) -> RandomState


pub(crate) fn with_fixed_keys() -> RandomState

Internal. Used by Default.


pub fn with_seed(key: usize) -> RandomState

Build a RandomState from a single key. The provided key does not need to be of high quality, but all RandomStates created from the same key will produce identical hashers. (In contrast to generate_with above)

This allows for explicitly setting the seed to be used.

Note: This method does not require the provided seed to be strong.


pub const fn with_seeds(k0: u64, k1: u64, k2: u64, k3: u64) -> RandomState

Allows for explicitly setting the seeds to used. All RandomStates created with the same set of keys key will produce identical hashers. (In contrast to generate_with above)

Note: If DOS resistance is desired one of these should be a decent quality random number. If 4 high quality random number are not cheaply available this method is robust against 0s being passed for one or more of the parameters or the same value being passed for more than one parameter. It is recommended to pass numbers in order from highest to lowest quality (if there is any difference).


pub fn hash_one<T: Hash>(&self, x: T) -> u64where Self: Sized,

Calculates the hash of a single value. This provides a more convenient (and faster) way to obtain a hash: For example:

    use std::hash::BuildHasher;
    use ahash::RandomState;

    let hash_builder = RandomState::new();
    let hash = hash_builder.hash_one("Some Data");

This is similar to:

    use std::hash::{BuildHasher, Hash, Hasher};
    use ahash::RandomState;

    let hash_builder = RandomState::new();
    let mut hasher = hash_builder.build_hasher();
    "Some Data".hash(&mut hasher);
    let hash = hasher.finish();

(Note that these two ways to get a hash may not produce the same value for the same data)

This is intended as a convenience for code which consumes hashes, such as the implementation of a hash table or in unit tests that check whether a custom Hash implementation behaves as expected.

This must not be used in any code which creates hashes, such as in an implementation of Hash. The way to create a combined hash of multiple values is to call Hash::hash multiple times using the same Hasher, not to call this method repeatedly and combine the results.

Trait Implementations§


impl BuildHasher for RandomState


fn build_hasher(&self) -> AHasher

Constructs a new AHasher with keys based on this RandomState object. This means that two different RandomStates will will generate AHashers that will return different hashcodes, but Hashers created from the same BuildHasher will generate the same hashes for the same input data.

        use ahash::{AHasher, RandomState};
        use std::hash::{Hasher, BuildHasher};
        let build_hasher = RandomState::new();
        let mut hasher_1 = build_hasher.build_hasher();
        let mut hasher_2 = build_hasher.build_hasher();
        assert_eq!(hasher_1.finish(), hasher_2.finish());
        let other_build_hasher = RandomState::new();
        let mut different_hasher = other_build_hasher.build_hasher();
        assert_ne!(different_hasher.finish(), hasher_1.finish());

type Hasher = AHasher

Type of the hasher that will be created.
1.71.0 · source§

fn hash_one<T>(&self, x: T) -> u64where T: Hash, Self: Sized, Self::Hasher: Hasher,

Calculates the hash of a single value. Read more

impl Clone for RandomState


fn clone(&self) -> RandomState

Returns a copy of the value. Read more
1.0.0 · source§

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

Performs copy-assignment from source. Read more

impl Debug for RandomState


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

Formats the value using the given formatter. Read more

impl Default for RandomState

Creates an instance of RandomState using keys obtained from the random number generator. Each instance created in this way will have a unique set of keys. (But the resulting instance can be used to create many hashers each or which will have the same keys.)

This is the same as RandomState::new()

NOTE: For safety this trait impl is only available available if either of the flags runtime-rng (on by default) or compile-time-rng are enabled. This is to prevent weakly keyed maps from being accidentally created. Instead one of constructors for RandomState must be used.


fn default() -> Self

Returns the “default value” for a type. Read more

Auto Trait Implementations§

Blanket Implementations§


impl<T> Any for Twhere T: 'static + ?Sized,


fn type_id(&self) -> TypeId

Gets the TypeId of self. Read more

impl<T> Borrow<T> for Twhere T: ?Sized,


fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

impl<T> BorrowMut<T> for Twhere T: ?Sized,


fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

impl<T> From<T> for T


fn from(t: T) -> T

Returns the argument unchanged.


impl<T, U> Into<U> for Twhere U: From<T>,


fn into(self) -> U

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.


impl<T> ToOwned for Twhere T: Clone,


type Owned = T

The resulting type after obtaining ownership.

fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more

fn clone_into(&self, target: &mut T)

Uses borrowed data to replace owned data, usually by cloning. Read more

impl<T, U> TryFrom<U> for Twhere U: Into<T>,


type Error = Infallible

The type returned in the event of a conversion error.

fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,


type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.