ios – 如何在swift中进行多重继承？

protocol Motion {
    func move()
}

extension Motion where Self: PetViewController {

    func move() {
        //Open mouth
    }

}

class PetViewController: UIViewController,Motion{
    var isLoud: Bool?

    func speak(){
        //Open Mouth
    }
}

class DogViewController:PetViewController {

    func bark() {

        self.speak()

        //Make Bark Sound
    }
}

class CatViewController: PetViewController {

    func meow() {

        self.speak()

        //Make Meow Sound


    }

}

//....

let cat = CatViewController()
cat.move()
cat.isLoud = false
cat.meow()