hash_str 0.2.0

Strings with a precomputed hash.
Documentation 
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use crate::hash_str::HashStr;
use std::collections::{HashMap,HashSet};
use core::hash::{BuildHasher,BuildHasherDefault,Hash,Hasher};

pub(crate) fn make_hash(value:&str)->u64{
	let not_random_state=ahash::RandomState::with_seeds(0,0,0,0);
	let mut hasher=not_random_state.build_hasher();
	hasher.write(value.as_bytes());
	hasher.finish()
}

// Just feed the precomputed hash into the Hasher. Note that this will of course
// be terrible unless the Hasher in question is expecting a precomputed hash.
impl Hash for HashStr{
	#[inline]
    fn hash<H:Hasher>(&self,state:&mut H){
        state.write_u64(self.precomputed_hash());
    }
}

/// A standard `HashMap` using `&HashStr` as the key type with a custom `Hasher`
/// that just uses the precomputed hash for speed instead of calculating it.
pub type HashStrMap<'a,V>=HashMap<&'a HashStr,V,BuildHasherDefault<IdentityHasher>>;

/// A standard `HashSet` using `&HashStr` as the key type with a custom `Hasher`
/// that just uses the precomputed hash for speed instead of calculating it.
pub type HashStrSet<'a>=HashSet<&'a HashStr,BuildHasherDefault<IdentityHasher>>;

/// The worst hasher in the world -- the identity hasher.
#[doc(hidden)]
#[derive(Default)]
pub struct IdentityHasher {
    hash: u64,
}

impl Hasher for IdentityHasher {
	#[inline]
    fn write_u64(&mut self, value: u64) {
        self.hash = value;
    }
    #[inline]
    fn write(&mut self, bytes: &[u8]) {
        self.hash = u64::from_ne_bytes(bytes.try_into().unwrap());
    }
    #[inline]
    fn finish(&self) -> u64 {
        self.hash
    }
}

#[test]
fn test_hashing() {
	let u1=&*HashStr::anonymous("the quick brown fox".to_owned());
	let u2=&*HashStr::anonymous("jumps over the lazy dog".to_owned());

	let mut hasher = IdentityHasher::default();
	u1.hash(&mut hasher);
	assert_eq!(hasher.finish(), u1.precomputed_hash());

	let mut hasher = IdentityHasher::default();
	u2.hash(&mut hasher);
	assert_eq!(hasher.finish(), u2.precomputed_hash());

	let mut hm = HashStrMap::<u32>::default();
	hm.insert(u1, 17);
	hm.insert(u2, 42);

	assert_eq!(hm.get(u1), Some(&17));
	assert_eq!(hm.get(u2), Some(&42));
}