Efficient, immutable, and thread-safe collection classes for Ruby. Hamster provides 6 Persistent Data Structures: Hash, Vector, Set, SortedSet, List, and Deque (which works as an immutable queue or stack). Hamster collections are immutable. Whenever you modify a Hamster collection, the original is preserved and a modified copy is returned. This makes them inherently thread-safe and shareable. At t