From: Raul Parolari <raulparolari@...>
Date: 2007-11-17T14:36:50+09:00
Subject: Re: Composition: Build objects from other objects

Thufir wrote:
> 
> then can you make the vw_bug go "vroooooom" and so forth?  What would be
> the usual way to do this in ruby?  When a car is instantiated, should an
> engine object get passed to the initializer method?
>
> thanks,
> 
> Thufir

I do not like (at first view) the idea of this design; it leads to, as 
Konrad has correctly observed, to start the car by saying:

    vw_bug.engine.vroom()

Should the car user know that he has to tell the car to ask the engine 
to rev up? Uhm..

Another take is the following; let's use a module Engine:

module Engine
  attr_accessor :type

  def initialize
    @type = "generic engine"
  end

  def vroom
    puts "vroooooom"
  end
end

class Vehicle
  include Engine

  def initialize
    super
  end
end

class Car < Vehicle
  def initialize
    super
  end
end

vw_bug = Car.new
vw_bug.vroom

I am not crazy of the 'Engine' Module, but I definitely like to ask the 
VW to wroom, without worrying about what is inside,

Raul

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