observer pattern by ruby

observer.rb

class Newspaper
  include Observable
  def deliver(news)
    changed
    @news = news
    notify_observers @news
  end
end
class Subscriber
  def update(news)
    p news
  end
end

newspaper = Newspaper.new

# add two subscribers
a = Subscriber.new
b = Subscriber.new
newspaper.add_observer(a)
newspaper.add_observer(b)

newspaper.deliver("some news")