Ruby extended_modules method which returns all modules a class or module has been extended with

extended_modules.rb

# Defines a method on modules and classes to output the modules it has been extended with.
# This works because extending class really just includes the module into the classes metaclass. 

class Module
  def extended_modules
    # this exposes the metaclass and for any code inside, self is scoped to the metaclass
    class << self
      self.included_modules
    end
  end
end

# Example:
# >> class A; end
# >> module Stuff; end
# >> A.extend Stuff
# >> A.extended_modules
# => [Stuff, Kernel]