buffer.rb

class Enumerator
  class Buffer
    attr_accessor :status

    def initialize(yielder, initial_status = nil)
      @buffer = []
      @yielder = yielder
      @status = initial_status
    end

    def push(item)
      @buffer.push(item)
    end
    alias << push

    def pop
      @buffer.pop
    end

    def clear
      @buffer.clear
      self
    end

    def empty?
      @buffer.empty?
    end

    def size
      @buffer.size
    end

    def flush
      return false if @buffer.empty?
      @yielder.yield(@buffer)
      @buffer = []
      true
    end
  end
end

module Enumerable
  def buffer(initial_status = nil, &block)
    Enumerator.new { |yielder|
      buffer = Enumerator::Buffer.new(yielder, initial_status)
      each { |*args|
        case args.size
        when 0
          block.call(buffer)
        when 1
          block.call(args.first, buffer)
        else
          block.call(args, buffer)
        end
      }
      buffer.flush
    }
  end
end