From: martindemello@... (Martin DeMello)
Date: 2003-05-17T02:00:35+09:00
Subject: make_collector

Got tired of perpetually writing if-then-else code to accumulate the
results of an iterator and return an array if no block was passed in.
(The somewhat hacked-up gensym class could probably use work - how
threadsafe is Singleton? Would using a class instance variable be
better?)

--------------------------------------
require 'singleton'

class Gensym
  include Singleton

  def initialize
    @n = 0
  end

  def next
    @n += 1
    "G#{@n}".intern
  end
end

def gensym
  Gensym.instance.next
end

class Module
  def make_collector(*args)
    args.each {|meth|
      oldmeth = gensym
      module_eval <<-here
      alias #{oldmeth} #{meth}
      def #{meth}(*args)
	retval = []
	#{oldmeth}(*args) {|x|
	  if block_given?
	    yield x
	  else
	    retval << x
	  end
	}
      end
      here
    }
  end
end

class Foo
  def initialize
    @ary = (1..10).to_a
  end

  def traverse
    @ary.each {|x| yield x}
  end

  make_collector(:traverse)
end

a = Foo.new
a.traverse {|x| p x}
p a.traverse