A Least Recently Used (LRU) cache is a key-value store that contains a set capacity for the number of elements it holds. When trying to add a new key-value pair, if cache.size == cache.capacity, the Least Recently Used key is removed.
An item in the cache is used every time its value is read, or it is assigned or cached using the cache method.
cache = LruCache.new(2)
|> LruCache.cache(:k1, :v1)
|> LruCache.cache(:k2, :v2)
# %LruCache{capacity: 2, lru: [:k1, :k2], size: 2, store: #HashDict<[k2: :v2, k1: :v1]>}
cache |> LruCache.read(:k1) # :k2 becomes least recently used key
# {%LruCache{capacity: 2, lru: [:k2, :k1], size: 2, store: #HashDict<[k2: :v2, k1: :v1]>}, :v1}
cache |> LruCache.cache(:k3, :v3) # :k2 is dropped and :k3 inserted
# %LruCache{capacity: 2, lru: [:k2, :k3], size: 2, store: #HashDict<[k3: :v3, k2: :v2]>}Just a quick bash at it for a kata, not really meant for production use. Would probably be better implemented as a GenServer backed by ETS.