extending.rb

require 'active_support/core_ext/class/removal'

class Class
  # Rubinius
  if defined?(Class.__subclasses__)
    def descendents
      subclasses = []
      __subclasses__.each {|k| subclasses << k; subclasses.concat k.descendents }
      subclasses
    end
  else
    # MRI
    begin
      ObjectSpace.each_object(Class.new) {}

      def descendents
        subclasses = []
        ObjectSpace.each_object(class << self; self; end) do |k|
          subclasses << k unless k == self
        end
        subclasses
      end
    # JRuby
    rescue StandardError
      def descendents
        subclasses = []
        ObjectSpace.each_object(Class) do |k|
          subclasses << k if k < self
        end
        subclasses.uniq!
        subclasses
      end
    end
  end
end

class Object
  def remove_subclasses_of(*superclasses) #:nodoc:
    Class.remove_class(*subclasses_of(*superclasses))
  end

  # Exclude this class unless it's a subclass of our supers and is defined.
  # We check defined? in case we find a removed class that has yet to be
  # garbage collected. This also fails for anonymous classes -- please
  # submit a patch if you have a workaround.
  def subclasses_of(*superclasses) #:nodoc:
    subclasses = []
    superclasses.each do |klass|
      subclasses.concat klass.descendents.select {|k| k.name.blank? || k.reachable?}
    end
    subclasses
  end

  def extended_by #:nodoc:
    ancestors = class << self; ancestors end
    ancestors.select { |mod| mod.class == Module } - [ Object, Kernel ]
  end

  def extend_with_included_modules_from(object) #:nodoc:
    object.extended_by.each { |mod| extend mod }
  end
end