open_close_example.rb

class SMSNotification < Notification
  def send
    # sends a sms notification
  end
end

class EmailNotification < Notification
  def send
   # sends an email with the notification
  end
end

class PushNotification < Notification
  def send
    # sends a push notification
  end
end

class Notification
  def send
    #
  end
  
  def self.send_notifications notifications_to_send
    notifications_to_send.each { |notification| notification.send }
  end
  
  # ...
end