Need for Mixins: what I have

mixins1.swift

protocol Observable {
    func observe(onUpdate: (Void) -> Void) ->  String
    func unobserve(key: String)
}

class ObservableDispatcher {
    var observerClosures: Dictionary<String, (Void) -> Void> = Dictionary<String, (Void) -> Void>()
    
    func observe(onUpdate: (Void) -> Void) -> String {
        let key = "key_\(observerClosures.count+1)_key"
        observerClosures[key] = onUpdate
        return key
    }
    
    func unobserve(key: String) {
        observerClosures.removeValueForKey(key)
    }
    
    func update() {
        for closure in self.observerClosures.values {
            closure()
        }
    }
}


class HDSViewModel: Observable {
    var observerClosures: Dictionary<String, (Void) -> Void> = Dictionary<String, (Void) -> Void>()
    
    let dispatcher = ObservableDispatcher()
    
    func observe(onUpdate: (Void) -> Void) -> String {
        return dispatcher.observe(onUpdate)
    }
    func unobserve(key: String) {
        dispatcher.unobserve(key)
    }

    func doSometing() {
      // Do Something
      self.dispatcher.update()
    }
}