The standard implemenation of LRU cache (hash table + doubly-linked list). All operations are in time complexity of O(1). This implementation is not thread-safe.
$ nimble install lrucache
See here
# create a new LRU cache with initial capacity of 1 items
let cache = newLRUCache[int, string](1)
cache[1] = "a"
cache[2] = "b"
# key 1 is not in cache, because key 1 is eldest and capacity is only 1
assert: 1 notin cache
assert: 2 in cache
# increase capacity and add key 1
cache.capacity = 2
cache[1] = "a"
assert: 1 in cache
assert: 2 in cache
# update recentness of key 2 and add key 3, then key 1 will be discarded.
echo cache[2]
cache[3] = "c"
assert: 1 notin cache
assert: 2 in cache
assert: 3 in cache