Class 'ViewController' has no initializers in swift

Question

Getting the complaint from the compiler when I am doing this

class ViewController: UIViewController {

    var delegate : AppDelegate
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        //self.appDelegate = UIApplication.sharedApplication().delegate;

    }

    @IBAction func getData(sender : AnyObject) {

    }

    @IBAction func LogOut(sender : AnyObject) {
    }
}

However, if I just add ? at the end of AppDelegate like below and the error is gone.

class ViewController: UIViewController {

    var delegate : AppDelegate?
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        //self.appDelegate = UIApplication.sharedApplication().delegate;

    }

    @IBAction func getData(sender : AnyObject) {

    }

    @IBAction func LogOut(sender : AnyObject) {
    }
}

I don't see optional keyword relevant to this error unless I am wrong.

Answer 1

The error could be improved, but the problem with your first version is you have a member variable, delegate, that does not have a default value. All variables in Swift must always have a value. That means that you have to set it up in an initializer which you do not have or you could provide it a default value in-line.

When you make it optional, you allow it to be nil by default, removing the need to explicitly give it a value or initialize it.