1# hashlink -- HashMap-like containers that hold their key-value pairs in a user controllable order
2
3[![Build Status](https://img.shields.io/circleci/project/github/kyren/hashlink.svg)](https://circleci.com/gh/kyren/hashlink)
4[![Latest Version](https://img.shields.io/crates/v/hashlink.svg)](https://crates.io/crates/hashlink)
5[![API Documentation](https://docs.rs/hashlink/badge.svg)](https://docs.rs/hashlink)
6
7This crate is a fork of
8[linked-hash-map](https://github.com/contain-rs/linked-hash-map) that builds on
9top of [hashbrown](https://github.com/rust-lang/hashbrown) to implement more up
10to date versions of `LinkedHashMap` `LinkedHashSet`, and `LruCache`.
11
12One important API change is that when a `LinkedHashMap` is used as a LRU cache,
13it allows you to easily retrieve an entry and move it to the back OR produce a
14new entry at the back without needlessly repeating key hashing and lookups:
15
16``` rust
17let mut lru_cache = LinkedHashMap::new();
18let key = "key".to_owned();
19// Try to find my expensive to construct and hash key
20let _cached_val = match lru_cache.raw_entry_mut().from_key(&key) {
21    RawEntryMut::Occupied(mut occupied) => {
22        // Cache hit, move entry to the back.
23        occupied.to_back();
24        occupied.into_mut()
25    }
26    RawEntryMut::Vacant(vacant) => {
27        // Insert expensive to construct key and expensive to compute value,
28        // automatically inserted at the back.
29        vacant.insert(key.clone(), 42).1
30    }
31};
32```
33
34Or, a simpler way to do the same thing:
35
36``` rust
37let mut lru_cache = LinkedHashMap::new();
38let key = "key".to_owned();
39let _cached_val = lru_cache
40    .raw_entry_mut()
41    .from_key(&key)
42    .or_insert_with(|| (key.clone(), 42));
43```
44
45This crate contains a decent amount of unsafe code from handling its internal
46linked list, and the unsafe code has diverged quite a lot from the original
47`linked-hash-map` implementation.  It currently passes tests under miri and
48sanitizers, but it should probably still receive more review and testing, and
49check for test code coverage.
50
51## Credit
52
53There is a huge amount of code in this crate that is copied verbatim from
54`linked-hash-map` and `hashbrown`, especially tests, associated types like
55iterators, and things like `Debug` impls.
56
57## License
58
59This library is licensed the same as
60[linked-hash-map](https://github.com/contain-rs/linked-hash-map) and
61[hashbrown](https://github.com/rust-lang/hashbrown), it is licensed under either
62of:
63
64* MIT license [LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT
65* Apache License 2.0 [LICENSE-APACHE](LICENSE-APACHE) or https://opensource.org/licenses/Apache-2.0
66
67at your option.
68