# LRU Cache with compile-time reference stability

* [crate](https://crates.io/crates/ref-stable-lru)
* [blog post][blog_post]

The main codes are copy from [lru-rs][lru-rs], very grateful for the project.

The main motivation for implementing this project is that `LRUCache` should allow multiple immutable references obtained through `get` method. Currently, this crate is under the active development stage. The purpose of this crate is to validate the new design pattern and hope to apply it to more collection libraries, preferably including std. As for this library itself, I would prefer its proposed new API to be merged to [upstream][lru-rs].

The main idea is separating the value operating permissions from the data structure itself. [The blog post][blog_post] elaborates the idea. You can also take a look at [uitest](./tests/ui/test.rs), which explains the API design goals.

## Example

Below is a simple example shows the main feature of `LRUCache`.

```rust
let mut cache = LruCache::new(NonZeroUsize::new(2).unwrap());

cache.scope(|mut cache, mut perm| {
    assert_eq!(cache.put("apple", "red", &mut perm), None);
    assert_eq!(cache.put("banana", "yellow", &mut perm), None);
    assert_eq!(cache.put("lemon", "yellow", &mut perm), Some("red"));

    let colors: Vec<_> = ["apple", "banana", "lemon", "watermelon"]
        .iter()
        .map(|k| cache.get(k, &perm))
        .collect();
    assert!(colors[0].is_none());
    assert_opt_eq(colors[1], "yellow");
    assert_opt_eq(colors[2], "yellow");
    assert!(colors[3].is_none());
});
```

[blog_post]:https://blog.cocl2.com/posts/rust-ref-stable-collection/
[lru-rs]:https://github.com/jeromefroe/lru-rs