Struct hashbrown::hash_map::RawEntryBuilder

pub struct RawEntryBuilder<'a, K, V, S, A: Allocator + Clone = Global> { /* private fields */ }

A builder for computing where in a HashMap a key-value pair would be stored.

See the HashMap::raw_entry docs for usage examples.

Examples

use hashbrown::hash_map::{HashMap, RawEntryBuilder};
use core::hash::{BuildHasher, Hash};

let mut map = HashMap::new();
map.extend([(1, 10), (2, 20), (3, 30)]);

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 0..6 {
    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);
    let builder: RawEntryBuilder<_, _, _> = map.raw_entry();
    assert_eq!(builder.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);
}

Implementations

impl<'a, K, V, S, A: Allocator + Clone> RawEntryBuilder<'a, K, V, S, A>

pub fn from_key<Q: ?Sized>(self, k: &Q) -> Option<(&'a K, &'a V)>where
    S: BuildHasher,
    K: Borrow<Q>,
    Q: Hash + Eq,

Access an immutable entry by key.

Examples

use hashbrown::HashMap;

let map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
let key = "a";
assert_eq!(map.raw_entry().from_key(&key), Some((&"a", &100)));

pub fn from_key_hashed_nocheck<Q: ?Sized>(
    self,
    hash: u64,
    k: &Q
) -> Option<(&'a K, &'a V)>where
    K: Borrow<Q>,
    Q: Eq,

Access an immutable entry by a key and its hash.

Examples

use core::hash::{BuildHasher, Hash};
use hashbrown::HashMap;

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()
}

let map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
let key = "a";
let hash = compute_hash(map.hasher(), &key);
assert_eq!(map.raw_entry().from_key_hashed_nocheck(hash, &key), Some((&"a", &100)));

pub fn from_hash<F>(self, hash: u64, is_match: F) -> Option<(&'a K, &'a V)>where
    F: FnMut(&K) -> bool,

Access an immutable entry by hash and matching function.

Examples

use core::hash::{BuildHasher, Hash};
use hashbrown::HashMap;

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()
}

let map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
let key = "a";
let hash = compute_hash(map.hasher(), &key);
assert_eq!(map.raw_entry().from_hash(hash, |k| k == &key), Some((&"a", &100)));

Trait Implementations

impl<K, V, S, A: Allocator + Clone> Debug for RawEntryBuilder<'_, K, V, S, A>

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

Formats the value using the given formatter.