From: Michael Fellinger <m.fellinger@...>
Date: 2008-11-19T19:36:38+09:00
Subject: Re: Is there a way to know what are the subclasses of a given class ?

On Wed, Nov 19, 2008 at 7:12 PM, Jesús Gabriel y Galán
<jgabrielygalan@gmail.com> wrote:
>> On 2008.11.19., at 10:10, Sandro Paganotti wrote:
>>
>>> [SOLVED]
>>>
>>> I just find out that you can call:
>>>
>>> A.constants --> ["B","C"]
>>>
>>> Thank you
>>>
>>> Sandro
>>>
>>> On Wed, Nov 19, 2008 at 10:10 AM, Sandro Paganotti <
>>> sandro.paganotti@gmail.com> wrote:
>>>
>>>> Hello
>>>>
>>>> Do you know if there's a trick to retrieve a list of all the subclasses
>>>> of
>>>> a given class ?
>>>>
>>>> class A
>>>>  class B
>>>>  end
>>>>  class C
>>>>  end
>>>> end
>>>>
>>>> like  A.subclasses  --> [B,C] ?
>
> As has been mentioned, in your example B and C are not subclasses of A.
> If you want to list all subclasses of a class you can do this:
>
> irb(main):001:0> class A
> irb(main):002:1> class << self
> irb(main):003:2> attr_accessor :subclasses
> irb(main):004:2> end
> irb(main):005:1> def self.inherited child
> irb(main):006:2> (A.subclasses ||= []) << child
> irb(main):007:2> end
> irb(main):008:1> end
> => nil
> irb(main):009:0> A.subclasses
> => nil
> irb(main):010:0> class B < A; end;
> irb(main):011:0* A.subclasses
> => [B]
> irb(main):012:0> class C < B; end;
> irb(main):013:0* A.subclasses
> => [B, C]
> irb(main):014:0> class D < A; end;
> irb(main):015:0* A.subclasses
> => [B, C, D]
>
> Hope this helps,
>
> Jesus.
>
>

Little different style maybe:

class A
  @subclasses = []
  def self.inherited(into) @subclasses << into end
  def self.subclasses() @subclasses end
end
# nil
class B < A
end
# nil
A.subclasses
# [B]

And a slower and hacky alternative:

require 'set'; found = Set.new; ObjectSpace.each_object(Class){|o|
found << o if o < A }
# 446
found
# #<Set: {B}>

^ manveru