From: Robert Klemme <shortcutter@...>
Date: 2009-08-13T04:50:06+09:00
Subject: Re: Class#descendants?

On 12.08.2009 21:30, Jason Lillywhite wrote:
> Ruby can do Class#ancestors but not Class#descendants.
> 
> I found this: http://termos.vemod.net/class-descendants
> 
> But it only works after you define a new inheritance. Is there a way to
> find descendants of a class that is already in place? For example:
> 
> Numeric.descendants
> => [Integer, Float, Complex]

Let me first state that I believe this is intentional: while sub classes 
need knowledge of their parent classes the opposite is not true.  In 
fact, that would create a kind of circular dependency.

Having said that, this is what you could do

require 'set'
h = Hash.new {|h,k| h[k] = Set.new}

ObjectSpace.each_object(Class) do |cl|
   cl.superclass.ancestors.each {|scl| h[scl] << cl}
end

p h[String]

You should keep in mind though that this is by no means static.  New 
classes can come in existence at any time.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/