iteration.rb

module BackwardIteration
  def self.included(base)
    if base.ancestors.include?(ForwardIteration)
      instance_methods.each do |method|
        base.class_eval do
          alias_method "#{method}_reverse", method

          define_method method do
            unbound = ForwardIteration.instance_method(method)
            unbound.bind(self).call
          end
        end
      end
    end
  end

  def map
    'Backward Iteration'
  end
end

module ForwardIteration
  def map
    'Forward Iteration'
  end
end

class SingleLinkedList
  include ForwardIteration
end

class DoubleLinkedList
  include ForwardIteration
  include BackwardIteration
end

puts ""

puts SingleLinkedList.new.map
#=> ForwardIteration

begin
  puts SingleLinkedList.new.map_reverse
rescue
  puts 'Single has no #map_reverse'
end

puts DoubleLinkedList.new.map
#=> ForwardIteration

puts DoubleLinkedList.new.map_reverse
#=> BackwardIteration