A simple ring buffer for Ruby.

ringbuffer.rb

class RingBuffer < Array
  attr_reader :max_size
 
  def initialize(max_size, enum = nil)
    @max_size = max_size
    enum.each { |e| self << e } if enum
  end
 
  def <<(el)
    if self.size < @max_size || @max_size.nil?
      super
    else
      self.shift
      self.push(el)
    end
  end
 
  alias :push :<<
end

This has a major bug. << by default means "push", so
a = RingBuffer.new(3)
a << "first"
a << "second"
a << "third" # a == ["first", "second", "third"]
# but now
a << "fourth" # a == ["fourth", "first", "second"]

Where one would expect after the fourth insertion, a would contain ["second", "third", "fourth"]. This is consistent with a RingBuffer being a data structure for MRU access, i.e oldest elements should be overwritten.

I fixed this on my fork, https://gist.github.com/4078106

@Nimster: many thanks for pointing it out, fixed. I'm still very much a Ruby newbie, and certainly much more so when I originally created this Gist.

Also check out this threadsafe one http://git.io/8RZjeA