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use std::hash::BuildHasher;
use std::hash::Hasher;
/// A hasher that directly uses the value provided to write_u64 as the hash
pub struct NoHasher(pub u64);
impl Hasher for NoHasher {
/// Returns the current value as the hash
fn finish(&self) -> u64 {
self.0
}
fn write(&mut self, _bytes: &[u8]) {
unimplemented!("NoHasher only supports write_u64");
fn write_u64(&mut self, i: u64) {
self.0 = i;
/// A builder for NoHasher. Starts with a hash of 0 and returns whatever value is passed to write_u64
#[derive(Default)]
pub struct NoHasherBuilder;
impl BuildHasher for NoHasherBuilder {
type Hasher = NoHasher;
fn build_hasher(&self) -> Self::Hasher {
NoHasher(0)
#[cfg(test)]
mod tests {
use crate::NoHasher;
use crate::NoHasherBuilder;
#[test]
fn test_no_hasher() {
let mut hasher = NoHasher(0);
hasher.write_u64(42);
assert_eq!(
hasher.finish(),
42,
"NoHasher should return the value passed to write_u64"
);
let builder = NoHasherBuilder;
let hasher = builder.build_hasher();
0,
"NoHasherBuilder should create a hasher with initial value 0"