http://blog.codegram.com/2011/4/understanding-class-instance-variables-in-ruby

class_instance_variable_inheritance.rb

module DogMixin
  class << self
    def included(base)
      base.extend ClassMethods
    end
  end

  module ClassMethods
    def assign(*names)
      @dog_names = names
    end

    def dog_names
      if (self.ancestors-[self]).include?(Owner)
        @dog_names.to_a + Owner.dog_names
      else
        @dog_names
      end
    end
  end
end

class Owner
  include DogMixin
  assign :base_dog
end

class Nerd < Owner
  assign :r2d2, :posix
end

class Emo < Owner
  assign :bill, :tom
end

class Hater < Owner
end