Crate hashlru

source ·
Expand description

HashLRU is a LRU cache.

It tries to follow the API exposed by a standard Rust HashMap while enforcing a limited memory footprint by limiting the number of keys using the LRU strategy, which is a quite common cache replacement policy.

HashLRU icon


Feels like a hash map:

use hashlru::Cache;

let mut cache = Cache::new(1000);

cache.insert("my-key", 123);
assert_eq!(Some(&123), cache.get(&"my-key"));

Drops unused entries:

use hashlru::Cache;

let mut cache = Cache::new(4);
cache.insert("key1", 10);
cache.insert("key2", 20);
cache.insert("key3", 30);
cache.insert("key4", 40);
cache.insert("key5", 50);
// key1 has been dropped, size is limited to 4
assert_eq!(Some(&"key2"), cache.lru());
assert_eq!(Some(&20), cache.get(&"key2"));
// getting key2 has made key3 the least recently used item
assert_eq!(Some(&"key3"), cache.lru());
assert_eq!(Some(&40), cache.get(&"key4"));
// getting key4 makes it the most recently used item
assert_eq!("[key3: 30, key5: 50, key2: 20, key4: 40]", format!("{}", cache));

More complex example:

use hashlru::Cache;

#[derive(Debug, Eq, PartialEq)]
struct Obj {
    name: String,
    scalar: usize,

impl Obj {
    fn new(name: &str, scalar: usize) -> Self {
        Obj{name: name.to_string(), scalar}

#[derive(Debug, Eq, PartialEq, Hash, Clone)]
struct Key {
    x: i64,
    y: i64,

impl Key {
    fn new(x: i64, y: i64) -> Self {
        Key{x, y}

let mut cache: Cache<Key, Obj> = Cache::new(2);
cache.insert(Key::new(1, 2), Obj::new("pim", 123));
cache.insert(Key::new(3, 9), Obj::new("pam", 456));
cache.insert(Key::new(-4, 0), Obj::new("pom", 789));
assert_eq!(2, cache.len());
cache.insert(Key::new(22, 10), Obj::new("pem", 0));
assert_eq!(Some(&Key::new(22, 10)), cache.mru());
assert_eq!(Some(&Key::new(3, 9)), cache.lru());
assert_eq!(Some(&Obj::new("pom", 789)), cache.get(&Key::new(-4, 0)));
assert_eq!(Some(&Key::new(-4, 0)), cache.mru());
assert_eq!(Some(&Key::new(3, 9)), cache.lru());
assert_eq!(Some(&Obj::new("pam", 456)), cache.get(&Key::new(3, 9)));
assert_eq!(Some(&Key::new(3, 9)), cache.mru());
assert_eq!(Some(&Key::new(22, 10)), cache.lru());

Thread-safe cache:

use hashlru::SyncCache;
use std::thread;

let cache: SyncCache<usize, usize> = SyncCache::new(50);

let cache1 = cache.clone();
let handle1 = thread::spawn(move || cache1.insert(1,2));
let cache2 = cache.clone();
let handle2 = thread::spawn(move || cache2.insert(3,4));


assert_eq!(Some(2), cache.get(&1));
assert_eq!(Some(4), cache.get(&3));


  • LRU cache which aims at being a drop-in replacement for a hash map.
  • Complete dump of a LRU cache, easily (de)serializable.
  • Iterator over a LRU cache, taking ownership.
  • Iterator over the keys of a LRU cache, taking ownership.
  • Iterator over the values of a LRU cache, taking ownership.
  • Iterator over a LRU cache.
  • Iterator over mutable entries of a LRU cache.
  • Iterator over the keys of a LRU cache.
  • Thread-safe LRU cache.
  • Iterator over the values of a LRU cache.