delegation.rb

module Delegator
  def self.extended(into)
    (class << into; self; end).send :attr_accessor, :delegates
    into.delegates = []

    into.send :define_method, :method_missing do |method, *args, &block|
      self.class.delegates.map{|delegate| send(delegate) }.each do |receiver|
        next unless receiver.respond_to?(method)
        return receiver.send(method, *args, &block)
      end
      super
    end
  end

  def delegate_to(*names)
    @delegates |= names
  end
end


# e.g.

if __FILE__ == $0
  class Engine
    def speed_up
      puts "Go Go Engine Speed Up!"
    end
  end

  class Chassis
    def transform
      puts "Go Go Chassis transformation!"
    end
  end

  class Car
    extend Delegator

    delegate_to :engine, :chassis
    attr_reader :engine, :chassis

    def initialize
      @engine = Engine.new
      @chassis = Chassis.new
    end
  end

  car = Car.new
  car.speed_up
  car.transform
end

###################


# output
ruby delegation.rb
Go Go Engine Speed Up!
delegation.rb:9:in `method_missing': unexpected return (LocalJumpError)
        from delegation.rb:7:in `each'
        from delegation.rb:7:in `method_missing'
        from delegation.rb:49