Chapter 2: Question about notification

📚 Official Books Combine: Asynchronous Programming with Swift
1

I do a simple notification test with combine.
Click postNotification button in ViewController that received notification successful.
Click removeReceiver button (set _receive to nil) in ViewController that NotificationReceiver object never deinit. Why?
Do I need to manual to cancel?

thanks

class NotificationReceiver {
    var _observer: AnyCancellable?
    
    deinit {
        print("[NotificationReceiver] deinit")
    }
    
    init() {
        _observer = NotificationCenter.default.publisher(for: .userClick, object: nil)
            .sink { notification in
                print("Received notification: \(notification)")
            }
    }
}

extension Notification.Name {
    static let userClick = Notification.Name("UserClick")
}

class ViewController: NSViewController {
    var _receiver: NotificationReceiver? = NotificationReceiver()
    
    @IBAction func postNotification(_ sender: Any) {
        NotificationCenter.default.post(name: .userClick, object: nil)
    }
    
    @IBAction func removeReceiver(_ sender: Any) {
        _receiver = nil
    }
}