From: Pat Maddox <pergesu@...>
Date: 2007-05-10T16:30:20+09:00
Subject: Re: The Factory Method

On 5/10/07, Enrique Comba Riepenhausen <ecomba@mac.com> wrote:
> 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
>
>
>

Go for it.

Pst