From: Zev Blut <rubyzbibd@...>
Date: 2006-08-08T18:36:01+09:00
Subject: Re: Automatic instantiation of subclasses

On Tue, 08 Aug 2006 18:19:12 +0900, Kilivor Kante <kilivor@hotmail.com>  
wrote:

> First sorry I am a beginner ;-( What I want to do is: automatically
> instantiate subclasses of a given class, say, A.
>
>   class A
>   end
>
>   class A1 < A
>   end
>
>   class A2 <A
>   end
>
> So I want to know the names of A subclasses: A1 and A2. Then instantiate
> via reflection. Is it possible?
>
> Using ObjectSpace it is possible to know all the instantiated objects of
> a class. But here no objects yet.

This is a fun pattern that I use a lot.
Here is a simple code snippet using ObjectSpace:

subclasses = []
ObjectSpace.each_object(Class) do |klass|
   if klass != A && klass.ancestors.include?(A)
     subclasses << klass
    end
end

# Then you can create new instances by calling new on the class
subclases.each do |klass|
   klass.new
end

Cheers,
Zev