gistfile1.txt

protocol Fooable {
    func foo() -> String
}

extension Fooable where Self : UIViewController
{
    func foo() -> String
    {
        return "foo"
    }
}

class ViewController: UIViewController, Fooable {
    override func viewDidLoad() {
        super.viewDidLoad()
        print(self.foo())
    }
}