Said ruby 1.9 will add a new useful feature named external iterator - the kind of iterator you used in Java/Cpp. It's interesting to implement one ourself by using callcc, in 1.8.6.

Note: It's easy to turn this piece of code into a module or make the external iterator available for all kinds of collections, try yourself :0

code:

data = %w/file edit search view tools options language buffers help/

class Array
  class Iterator
    attr_accessor :cc, :next_cc
    attr_accessor :value, :next_value
   
    def next?
      @next_value
    end
   
    def next
      @value = @next_value
      callcc do |cc|
        @next_cc = cc
        @cc.call
      end
      @value
    end
   
  end
 
  def iterator
    @iter = Iterator.new
    callcc do |cc|
      @iter.next_cc = cc
      each do |obj|
        callcc do |cc2|
          @iter.cc = cc2
          @iter.next_value = obj
          @iter.next_cc.call
        end
      end
      @iter.next_value = nil
      @iter.next_cc.call
    end
    @iter
  end
end

iter = data.iterator
puts iter.next while iter.next?