Swift: How to declare a static member variable which is a class

Question

I'm trying to declare a class which has a static variable which I want to set to an object of the class i.e.

class MyViewController: UIViewController {
      @IBOutlet weak var title: UILabel!

      static var staticSelf:MyViewController

This declaration generates the following error:

"class var declaration requires an initializer expression or getter/setter specifier".

So I tried several attempts at adding an initialzer but just was getting more or different compilation errors. So instead I tried adding a getter/setter specifier as it says in the error, but this is resulting in an infinite loop when run. I've tried several versions, this is the latest:

class MyViewController: UIViewController {

  @IBOutlet weak var title: UILabel!

  static var staticSelf:MyViewController {
    set (selfInstance) {
        MyViewController.staticSelf = selfInstance
    }
    get {
        return MyViewController.staticSelf
    }
  }

  override func viewDidLoad() {
    super.viewDidLoad()
    MyViewController.staticSelf = self
  }
}

The initial attempt at the implementation of the setter method was staticSelf = selfInstance, XCode flagged this as an error and auto-corrected to self.staticSelf = selfInstance, but that results in an infinate loop, so I changed it to MyViewController.staticSelf = selfInstance, but that too creates an infinate loop.

I've tried a thousand things to get this set up and could have done it in 3 seconds with objective-C , and am getting very fed up with Swift right now.

Answer 1

The basic example

class MyClass {
    static var string: String
}

does not work because unitialized variables have nil value. However, in Swift you can assign nil only to optional variables.

You have two options:

1. Declare the variable as optional

   static var string: String?
   

   or

   static var string: String? = nil
   

2. Initialize with a non-nil value:

   static var string: String = "some value"
   

If your aim is to create a singleton, then see the official Apple guide for the solution:

class MyViewController: UIViewController {
    static let staticSelf = MyViewController()
}