Observing.swift

final class Event: KeyValueObservable {
    let observationStore = ObservationStore<Event>()
    
    var title: String = "Initial Title" {
        didSet {
            didChangeValue(for: \Event.title)
        }
    }
}

final class ViewController: UIViewController {
    let event = Event()
    
    @IBOutlet weak var label: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        event.addObserver(self, keyPath: \.title, options: .initial) { (observer, title) in
            observer.label.text = title
        }
    }
    
    @IBAction func changeTitle(_ sender: Any) {
        event.title = "New Title"
    }
}