use crate::FxHasher;
/// Type alias for a hashmap using the `fx` hash algorithm with [`FxSeededState`].
#[cfg(feature = "std")]
pub type FxHashMapSeed<K, V> = std::collections::HashMap<K, V, FxSeededState>;
/// Type alias for a hashmap using the `fx` hash algorithm with [`FxSeededState`].
#[cfg(feature = "std")]
pub type FxHashSetSeed<V> = std::collections::HashSet<V, FxSeededState>;
/// [`FxSeededState`] is an alternative state for `HashMap` types, allowing to use [`FxHasher`] with a set seed.
///
/// ```
/// # use std::collections::HashMap;
/// use rustc_hash::FxSeededState;
///
/// let mut map = HashMap::with_hasher(FxSeededState::with_seed(12));
/// map.insert(15, 610);
/// assert_eq!(map[&15], 610);
/// ```
#[derive(Clone)]
pub struct FxSeededState {
seed: usize,
}
impl FxSeededState {
/// Constructs a new `FxSeededState` that is initialized with a `seed`.
pub const fn with_seed(seed: usize) -> FxSeededState {
Self { seed }
}
}
impl core::hash::BuildHasher for FxSeededState {
type Hasher = FxHasher;
fn build_hasher(&self) -> Self::Hasher {
FxHasher::with_seed(self.seed)
}
}
#[cfg(test)]
mod tests {
use core::hash::BuildHasher;
use crate::FxSeededState;
#[test]
fn cloned_seeded_states_are_equal() {
let seed = 2;
let a = FxSeededState::with_seed(seed);
let b = a.clone();
assert_eq!(a.seed, b.seed);
assert_eq!(a.seed, seed);
assert_eq!(a.build_hasher().hash, b.build_hasher().hash);
}
#[test]
fn same_seed_produces_same_hasher() {
let seed = 1;
let a = FxSeededState::with_seed(seed);
let b = FxSeededState::with_seed(seed);
// The hashers should be the same, as they have the same seed.
assert_eq!(a.build_hasher().hash, b.build_hasher().hash);
}
#[test]
fn different_states_are_different() {
let a = FxSeededState::with_seed(1);
let b = FxSeededState::with_seed(2);
assert_ne!(a.build_hasher().hash, b.build_hasher().hash);
}
}