From: Enrique Comba Riepenhausen <ecomba@...>
Date: 2007-05-10T17:04:33+09:00
Subject: Re: The Factory Method


On 10 May 2007, at 09:30, Pat Maddox wrote:

> 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.

Done ;) http://www.rubypatterns.org/doku.php/ 
gang_of_four_patterns:factory_method

>
> Pst
>