From: Daniel Berger <djberg96@...>
Date: 2006-12-03T08:15:06+09:00
Subject: Factory pattern, abstract base class

Hi all,

I'm trying to setup an abstract base class as a factory for its
subclasses.  The below code fails, as it always returns an instance of
Foo::Bar instead of one of its subclasses.

module Foo
   class Bar
      def initialize(arg)
         return if self.class != Foo::Bar
         case arg.downcase
            when 'baz'
               return Baz.new(arg)
            when 'zap'
               return Zap.new(arg)
         end
      end
   end

   class Baz < Bar
   end

   class Zap < Bar
   end
end

fb = Foo::Bar.new('baz')
p fb # Returns Foo::Bar, but I want Foo::Baz

Perhaps my whole approach is wrong.  What is the proper way to achieve
what I'm after (without resorting to making Bar a module)?

Thanks,

Dan