Why can the keyword “weak” only be applied to class and class-bound protocol types

Question

When I\'m declaring variables as weak in Swift, I sometimes get the error message from Xcode:

\'weak\' may only be applied to class and

Answer 1

protocol PenguinDelegate: class {
    func userDidTapThePenguin()
}

class MyViewController: UIViewController {
    weak var delegate: PenguinDelegate?
}

If you type class after your protocol it works as well and seems more appropriate that for NSObjectProtocol.