AppleDesignPatterns7.swift

enum NotificationName {
    case emailChangeNotification
}


protocol StateChangeObserver : class {
    func didChange(_ notification: NotificationName, value: String)
}


class LoginData {
    weak var observer:StateChangeObserver?
    
    var email: String = "" {
        didSet {
            observer?.didChange(.emailChangeNotification, value: email)
        }
    }
}