A persistent collection with semantics roughly equivalent to a ring buffer: acts like a queue, but has a predetermined maximum capacity; items added after that capacity is exceeded implicitly eject items from the front of the queue to make room.

Implements all the relevant Clojure interfaces, but none of the java interop interfaces; pull requests welcome.

Possible optimization: keep a reference to unused items until some new item overwrites it. This is easier and faster, but if you have a queue with very large objects (or a very large, mostly-empty queue), you may see memory leaks. The performance gain is probably not worth it, but I suppose that's a tradeoff some may not be willing to make.

amalloy.ring-buffer> (into (ring-buffer 3) '(a b))
(a b)
amalloy.ring-buffer> (into (ring-buffer 3) '(a b c d e))
(c d e)
amalloy.ring-buffer> (pop (into (ring-buffer 3) '(a b c d e)))
(d e)
amalloy.ring-buffer> (peek (into (ring-buffer 3) '(a b c d e)))
c

See the ring-buffer Clojars page for Leiningen and Maven install snippets.

Copyright © 2012 Alan Malloy

Distributed under the Eclipse Public License, the same as Clojure.