Swift KVO

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        
        let user = User()
        
        let name1 = Name()
        name1.first = "bob"
        
        let name2 = Name()
        name2.first = "john"
        
        user.name = name1
        
        user.name = name2
        name2.first = "dude"
    }
}

class Name: NSObject {
    dynamic var first: NSString?
    dynamic var last: NSString?
}

class User: NSObject {
    private var kvoContextName: UInt8 = 1
    
    var name: Name? {
        didSet(oldName) {
            print("did set")
            if let oldName = oldName {
                print("removing")
                oldName.removeObserver(self, forKeyPath: "first")
            }
            
            if let name = name {
                print("adding")
                name.addObserver(self, forKeyPath: "first", options: NSKeyValueObservingOptions.New, context: &kvoContextName)
            }
        }
    }
    
    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
        if context == &kvoContextName {
            print("observed")
        }
    }
    
    deinit {
        print("goodbye")
        if let name = name {
            name.removeObserver(self, forKeyPath: "first")
        }
    }
}