From: Daniel Schierbeck <daniel.schierbeck@...>
Date: 2005-12-02T03:32:32+09:00
Subject: Re: abstract class

hochherz wrote:
> hey
> 
> is there something like abstract classes in ruby?
> somehow a class i could not create but wich is a superclass of some 
> classes.
> 
> thanks
> olaf

   class Class
     alias_method :__new__, :new
   end

   module NonInstantiable
     def self.included(klass)
       super
       klass.module_eval do
         def self.new
           raise "Cannot instantiate abstract class #{self}"
         end

         def self.inherited(subklass)
           subklass.module_eval do
             def self.new(*args, &block)
               __new__(*args, &block)
             end
           end
         end
       end
     end
   end

   class BaseKlass
     include NonInstantiable
   end

   class SubKlass < BaseKlass; end

   puts SubKlass.new
   puts BaseKlass.new