gistfile1.txt

protocol Fooable {
    func foo() -> String
}

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

protocol FooableView : Fooable {}

extension FooableView where Self : UIView
{
    func foo() -> String
    {
        return "foo view"
    }
}

extension UIView: FooableView {}
protocol FooableButton : Fooable {}
extension FooableButton where Self : UIButton
{
    func foo() -> String
    {
        return "foo button"
    }
}

extension UIButton: FooableButton {}

class ViewController: UIViewController, Fooable {
    override func viewDidLoad() {
        super.viewDidLoad()
        print(self.foo())
        
        let v = UIView()
        print(v.foo())
        
        let b = UIButton()
        print(b.foo())
        
        
        
    }
}