DependencyInversion-1.swift

class Notifier {
    private var notificationReceiver: NotificationReceiver
    init(receiver: NotificationReceiver) {
        self.notificationReceiver = receiver
    }
    
    func somethingHappened() {
        notificationReceiver.receiveNotification()
    }
}

class NotificationReceiver {
    func receiveNotification() {
        // Do something
    }
}