Averiguando los Descendientes de una Clase (descendants)

Véase:

• The ObjectSpace module contains a number of routines that interact with the garbage collection facility and allow you to traverse all living objects with an iterator.

• each_object([module]) {|obj| ... } Calls the block once for each living, nonimmediate object in this Ruby process.

  If module is specified, calls the block for only those classes or modules that match (or are a subclass of) module.

  Returns the number of objects found. Immediate objects (Fixnums, Symbols true, false, and nil) are never returned.

[~/TheRubyProgrammingLanguageDrive/Chapter7ClassesAndModules]$ cat descendantsofaclass.rb 
require 'pp'

class Parent
  def self.descendants
    ObjectSpace.each_object(Class).select { |klass| klass < self }
  end
end

class Child < Parent
end

class GrandChild < Child
end

pp Parent.descendants # [GrandChild, Child]
pp Child.descendants  # [GrandChild]

[~/TheRubyProgrammingLanguageDrive/Chapter7ClassesAndModules]$ ruby descendantsofaclass.rb 
[GrandChild, Child]
[GrandChild]