aosp12/external/rust/crates/hashlink

hashlink -- HashMap-like containers that hold their key-value pairs in a user controllable order

This crate is a fork of linked-hash-map that builds on top of hashbrown to implement more up to date versions of LinkedHashMap LinkedHashSet, and LruCache.

One important API change is that when a LinkedHashMap is used as a LRU cache, it allows you to easily retrieve an entry and move it to the back OR produce a new entry at the back without needlessly repeating key hashing and lookups:

let mut lru_cache = LinkedHashMap::new();
let key = "key".to_owned();
// Try to find my expensive to construct and hash key
let _cached_val = match lru_cache.raw_entry_mut().from_key(&key) {
    RawEntryMut::Occupied(mut occupied) => {
        // Cache hit, move entry to the back.
        occupied.to_back();
        occupied.into_mut()
    }
    RawEntryMut::Vacant(vacant) => {
        // Insert expensive to construct key and expensive to compute value,
        // automatically inserted at the back.
        vacant.insert(key.clone(), 42).1
    }
};

Or, a simpler way to do the same thing:

let mut lru_cache = LinkedHashMap::new();
let key = "key".to_owned();
let _cached_val = lru_cache
    .raw_entry_mut()
    .from_key(&key)
    .or_insert_with(|| (key.clone(), 42));

This crate contains a decent amount of unsafe code from handling its internal linked list, and the unsafe code has diverged quite a lot from the original linked-hash-map implementation. It currently passes tests under miri and sanitizers, but it should probably still receive more review and testing, and check for test code coverage.

Credit

There is a huge amount of code in this crate that is copied verbatim from linked-hash-map and hashbrown, especially tests, associated types like iterators, and things like Debug impls.

License

This library is licensed the same as linked-hash-map and hashbrown, it is licensed under either of:

• MIT license LICENSE-MIT or http://opensource.org/licenses/MIT
• Apache License 2.0 LICENSE-APACHE or https://opensource.org/licenses/Apache-2.0

at your option.