ruby descendants method

descendants.rb

# ruby1.9
class Class
  def descendants
    ObjectSpace.each_object(::Class).select {|klass| klass < self }
  end
end


# Ruby pre-1.8.7:
class Class
  def descendants
    result = []
    ObjectSpace.each_object(::Class) {|klass| result << klass if klass < self }
    result
  end
end

class Cat < Animal
end

class Dog < Animal
end

Animal.descendants          # > [Cat, Dog]