From: Pit Capitain <pit@...>
Date: 2005-12-06T17:30:43+09:00
Subject: Re: Subclassing Class.

John Carter schrieb:
> 
> On to the next step. Let's rename Foo to AbstractFoo
> 
> Now I wanted
>   class AbstractFoo < Class
>   end
> 
> and you have given me that. But that was merely the first step in my 
> agenda.
> 
> I actually also want....
>   class ConcreteFooClass < AbstractFooClass
>   end
> 
>   class OtherConcreteFooClass < AbstractFooClass
>   end
> that polymorphically inherits behaviour from AbstractFooClass.

John, I'm not sure what you really need, but I think that the singleton 
class approach that others have suggested gives you the desired behaviour:

   class Foo
     def self.new fu, stuff
       super "#{fu} and #{stuff}"
     end
     def initialize things
       puts "new Foo with #{things}"
     end
   end

   Foo.new "abstract fu", "abstract stuff"
   # => new Foo with abstract fu and abstract stuff

   class ConcreteFoo < Foo
     def self.new fu
       super fu, "concrete stuff"
     end
     def initialize things
       print "ConcreteFoo: "
       super
     end
   end

   ConcreteFoo.new "concrete fu"
   # => ConcreteFoo: new Foo with concrete fu and concrete stuff

The class ConcreteFoo inherits behaviour from the class Foo and 
ConcreteFoo's singleton class inherits from Foo's singleton class.

I don't know whether this still works in Ruby 1.9, though.

Regards,
Pit