swift如何传递UIViewController类型的参数<XXXDelegate>

Question

I have this function to present signin/signup modal view controller. The parameter passed has to be UIViewController<AuthViewControllerDelegate> ( UIViewController for presenting method, AuthViewControllerDelegate for delegate method)

static func checkAuthError(controller: UIViewController<AuthViewControllerDelegate>, err: NSError) {
    if err.code == 401 {
        let authViewController = viewControllerWithIdentifier("AuthViewController") as! AuthViewController
        authViewController.delegate = controller
        controller.presentViewController(authViewController, animated: true, completion: nil)
    }
}

But I can't pass the objective c style type. Do I have to pass the same controller twice, with different types?

Answer 1

You could choose either the class or protocol type for the method argument and conditionally cast it to the other:

func checkAuthError(controller: UIViewController, err: NSError) {
    ...
    if authDelegate = controller as? AuthViewControllerDelegate {
        ...
    }
}

Alternatively, you could use a generic type constraint:

func checkAuthError<T: UIViewController where T: AuthViewControllerDelegate>(controller: T, err: NSError) {
    ...
}

Answer 2

It sounds like

func checkAuthError<T: UIViewController where T: AuthViewControllerDelegate>(controller: T, err: NSError) {
    ...
}

will be deprecated soon, replaced by:

func checkAuthError<T: UIViewController>(controller: T, err: NSError)  where T: AuthViewControllerDelegate {
    ...
}

For clarity, the where clause comes after any return values.