The main codes are copy from 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.
The main idea is separating the value operating permissions from the data structure itself. I'll give an elaboration in my blog post later. You can also take a look at uitest, which explains the API design goals.
Below is a simple example shows the main feature of LRUCache.
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());
});