From: Enrique Comba Riepenhausen <ecomba@...>
Date: 2007-05-10T16:24:31+09:00
Subject: Re: The Factory Method

Hey Pat!

On 10 May 2007, at 09:16, Pat Maddox wrote:

>
> One clue is that the example is coded in Java, vs smalltalk.  The
> reason for that is that Smalltalk doesn't really have the problem
> they're solving here.  An "interface" is just going to be a bunch of
> methods with the same method names and signatures.
>
> I'm sure they discusss it in DP, but you don't need to implement this
> pattern with an abstract class.  That's just there because you want
> common behavior.  So how do you implement this pattern in Ruby?
>
> class AmericanCoffeeShop
>  def make_coffee
>    Coffee.new :ingredients => [ :water, :mud ]
>  end
> end
>
> class ItalianCoffeeShop
>  def make_coffee
>    Espresso.new
>  end
> end
>
> Simple, you've implemented the factory method pattern.  We have an
> interface - make_coffee - and each class can instantiate an object of
> whatever kind it wants.
>
> If some client code needs to have a coffee made, you can just pass it
> an instance of either of those classes and it'll run fine.
>
> Shared behavior can be provided by a mixin (whereas in Java you need a
> superclass).
>
> module CoffeeProvider
>  def order
>    take_payment
>    give_change
>    make_coffee
>  end
> end
>
> class AmericanCoffeeShop
>  include CoffeeProvider
>
>  def make_coffee
>    Coffee.new :ingredients => [ :water, :mud ]
>  end
> end
>
> class ItalianCoffeeShop
>  include CoffeeProvider
>
>  def make_coffee
>    Espresso.new
>  end
> end
>
> Now we've achieved the desired behavior.  We've defined the high-level
> behavior of taking an order, but placed the responsibility on
> lower-level implementation details in another class.  Now anyone can
> come along and write a class that knows how to provide an order of
> coffee, all without any foresight from the initial author of
> CoffeeProvider.
>
> Pat
>

Thanks a lot for the input!

Do you mind if I post your answer in Ruby Patterns? http:// 
www.rubypatterns.org