Struct identity_hash::IdentityHasher

pub struct IdentityHasher<T>(_, _, _);

For an enabled type T, a IdentityHasher<T> implements std::hash::Hasher and uses the value set by one of the write_{u8, u16, u32, u64, usize, i8, i16, i32, i64, isize} methods as its hash output.

IdentityHasher does not implement any hashing algorithm and can only be used with types which can be mapped directly to a numeric value. Out of the box IdentityHasher is enabled for u8, u16, u32, u64, usize, i8, i16, i32, i64, and isize. Types that should be used with IdentityHasher need to implement IdentityHashable and by doing so assert that their Hash impl invokes only one of the Hasher::write_{u8, u16, u32, u64, usize, i8, i16, i32, i64, isize} methods exactly once.

Examples

See also BuildIdentityHasher, IntMap and IntSet for some easier usage examples. See IdentityHashable for use with custom types.

use identity_hash::IdentityHasher;
use std::{collections::HashMap, hash::BuildHasherDefault};

let mut m: HashMap::<u8, char, BuildHasherDefault<IdentityHasher<u8>>> =
    HashMap::with_capacity_and_hasher(2, BuildHasherDefault::default());

m.insert(0, 'a');
m.insert(1, 'b');

assert_eq!(Some(&'a'), m.get(&0));
assert_eq!(Some(&'b'), m.get(&1));

Trait Implementations

impl<T> Clone for IdentityHasher<T>

fn clone(&self) -> Self

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T> Debug for IdentityHasher<T>

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

Formats the value using the given formatter.

impl<T> Default for IdentityHasher<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T: IdentityHashable> Hasher for IdentityHasher<T>

fn write(&mut self, _: &[u8])

Writes some data into this Hasher.

fn write_u8(&mut self, n: u8)

Writes a single u8 into this hasher.

fn write_u16(&mut self, n: u16)

Writes a single u16 into this hasher.

fn write_u32(&mut self, n: u32)

Writes a single u32 into this hasher.

fn write_u64(&mut self, n: u64)

Writes a single u64 into this hasher.

fn write_usize(&mut self, n: usize)

Writes a single usize into this hasher.

fn write_i8(&mut self, n: i8)

Writes a single i8 into this hasher.

fn write_i16(&mut self, n: i16)

Writes a single i16 into this hasher.

fn write_i32(&mut self, n: i32)

Writes a single i32 into this hasher.

fn write_i64(&mut self, n: i64)

Writes a single i64 into this hasher.

fn write_isize(&mut self, n: isize)

Writes a single isize into this hasher.

fn finish(&self) -> u64

Returns the hash value for the values written so far.

fn write_u128(&mut self, i: u128)

Writes a single u128 into this hasher.

fn write_i128(&mut self, i: i128)

Writes a single i128 into this hasher.

fn write_length_prefix(&mut self, len: usize)

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

Writes a length prefix into this hasher, as part of being prefix-free.

fn write_str(&mut self, s: &str)

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

Writes a single str into this hasher.

impl<T> Copy for IdentityHasher<T>