How to do multi-inheritance in swift?

As stated in the comments by @Paulw11 is correct. Here is an example that involves A & B inheriting from C. Which I have named DogViewController and CatViewController (which inherits form PetViewController). You can see how a protocol might be useful. This is just an ultra basic example.

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()

You can't have multiple inheritance in Swift, the way to go is to look at Protocols, but it is a rather big topic to be discussed in an answer.

There are also many other questions with the same scope