# File lib/SubclassTracking.rb, line 3
def self.extended(klazz)
  (class <<klazz; self; end).send :attr_accessor,  :subclasses
  (class <<klazz; self; end).send :define_method, :inherited do |clzz|
    klazz.subclasses << clzz
    super
  end
  klazz.subclasses = []
  end