From: Thufir <hawat.thufir@...>
Date: 2007-11-18T05:02:12+09:00
Subject: Re: Composition: Build objects from other objects

On Sat, 17 Nov 2007 22:40:20 +0900, Liam wrote:


> v=Vehicle.new(Engine.new)
> v.vroom
> v.engine=MustangEngine.new
> v.vroom
> 
> 
> As far as comparison to Java, this example uses duck typing.  As long as
> it vrooms, you can use it as an engine for your vehicle.

Hehe, fair enough.  Ok, enough Java, it was just an entry point (although 
I would be interested to hear how this is addressed in other OOP oriented 
languages).  What stands out about the above is:

1.)  I don't follow all of the syntax, some of it's over my head (which 
is certainly ok).

2.) The engine is being instantiated *outside* of the class definition.  
I was assuming that the engine would be created in the vehicle's 
initialize method.  The above technique is to specify the engine when the 
car is "manufactured" by passing a new instance of Engine into the new 
Vehicle instance.



-Thufir