In-Memory Caches

Recipe	Crates	Categories
Use a Least Recently Used (LRU) Cache
`cached`
`moka`

Consider the following Rust crates for your in-memory caching needs: lru⮳, moka⮳, and cached⮳.

Use a Least Recently Used (LRU) Cache

lru⮳ provides a fast Least Recently Used (LRU) cache for Rust. LRU is a common data structure used to limit the size of a cache by discarding the Least Recently Used (accessed) items when the cache reaches its capacity.

use std::num::NonZeroUsize;

use lru::LruCache;

fn main() {
    // Create an LRU cache with a capacity of 3
    let mut cache = LruCache::new(NonZeroUsize::new(3).unwrap());

    // Insert some key-value pairs into the cache
    cache.put(1, "one");
    cache.put(2, "two");
    cache.put(3, "three");

    // Access some entries
    println!("a) value for key 1: {:?}", cache.get(&1)); // Should print "Value for key 1: Some("one")"
    assert_eq!(*cache.get(&2).unwrap(), "two");
    assert_eq!(cache.get(&3), Some(&"three"));
    assert!(cache.get(&4).is_none());

    // Insert another entry, causing the least recently used entry to be evicted
    cache.put(4, "four");

    // The cache now contains keys 2, 3, and 4
    println!("b) value for key 1: {:?}", cache.get(&1)); // Should print "Value for key 1: None"
    println!("b) value for key 3: {:?}", cache.get(&3)); // Should print "Value for key 3: Some("three")"
    println!("b) value for key 4: {:?}", cache.get(&4)); // Should print "Value for key 4: Some("four")"

    // Insert another entry, causing another eviction
    cache.put(5, "five");

    // The cache now contains keys 3, 4, and 5
    println!("Value for key 2: {:?}", cache.get(&2)); // Should print "Value for key 2: None"
    println!("Value for key 4: {:?}", cache.get(&4)); // Should print "Value for key 4: Some("four")"
    println!("Value for key 5: {:?}", cache.get(&5)); // Should print "Value for key 5: Some("five")"

    {
        // Returns a mutable reference to the value of the key in the cache or
        // `None``, if it is not present in the cache.
        // Moves the key to the head of the LRU list, if it exists.
        let v = cache.get_mut(&5).unwrap();
        *v = "new value";
        assert_eq!(cache.get_mut(&5), Some(&mut "new value"));

        assert_eq!(cache.get_mut(&6), None);
    }
}