From: Sean O'Halpin <sean.ohalpin@...>
Date: 2005-10-24T20:40:06+09:00
Subject: Re: How to find all the subclasses of a class?

On 10/24/05, Horacio Sanson <hsanson@moegi.waseda.jp> wrote:
>
> I want to be able to list and instatiate all subclasses of a class to create a
> Factory type pattern,  I want to be able to do something like
>
> subclasses = Array.new
>
> ## Magic code that puts all subclasses of a class in
> ##  the subclasses array
> subclasses = get_subclasses( .... )
>
> subclasses.each { |subclass|
>        return subclass.new if condition == true
> end
>
>
> sorry I am very new to Ruby and have no idea on how to do this.
> any help is appreciated.
>
>
> Horacio

Something like this should get you started (though don't expect it to
be efficient - it basically queries every object in the system to find
the subclasses):

class A
end

class B < A
end

class C < B
end

class Class
  def subclasses
    class_hash = {}
    ObjectSpace.each_object do |obj|
      if Class == obj.class
        if obj.ancestors.include? self
          class_hash[obj] = true
        end
      end
    end
    class_hash.keys
  end
end

p A.subclasses
#=> [C, B, A]

Regards,

Sean