Swift Optional of Optional

Question

For a project of mine, I have to create a proxy AppDelegate that will forward calls to a another AppDelegate.

UIApplicationDelegate havs a var window: UIWindow

Answer 1

The declaration of the property is

optional var window: UIWindow? { get set }

The optional in the beginning means that the property doesn't have to be there at all, that's the second ?.

UIApplicationDelegate is a protocol, the class that implements it doesn't have to implement everything.