enumerable_prelude.rb

class Module
  # call-seq:
  #   enumerable name
  #
  # Lets the method named as +name+ return an enumerator if no block is
  # given.
  #
  #   class N
  #     enumerable def numbers
  #       yield 1
  #       yield 2
  #       yield 3
  #     end
  #   end
  #   N.new.numbers.to_a            #=> [1, 2, 3]
  def enumerable(*names)
    names.each do |name|
      m = instance_method(name)
      define_method(name) do |*args, &block|
        return self.to_enum(__callee__, *args) unless block
        m.bind(self).(*args, &block)
      end
    end
  end
end