DependencyInversion-2.swift

protocol Receiver {
    func receiveNotification()
}

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

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