公告

// Any type can be made Announceable
extension String : Announceable { }

let announcer = Announcer()

// Subscribe to observe values of an Announceable type
let subscription = announcer.when(String.self) { (aString, anAnnouncer) in
    print("World says: \(aString)")
}

// Notify observers by announcing an Announceable value
announcer.announce("Drink Water!")

// Stop observing by removing the subscription object
announcer.remove(subscription: subscription)

// Alternatively, use an arbitrary object for managing subscriptions:
announcer.when(String.self, subscriber:self) { (aString, anAnnouncer) in
    print("Received announcement: \(aString)")
}

// Unsubscribe when no longer interested
announcer.ubsubscribe(self)