Optional binding succeeds if it shouldn't

Question

This is what I posted as a possible solution to Traverse view controller hierarchy in Swift (slightly modified):

extension UIViewController {

    func trave         


        

Answer 1

If you try to conditionally cast an object of type UINavigationController to a UICollectionViewController in a Playground:

var nc = UINavigationController()

if let vc = nc as? UICollectionViewController {
    println("Yes")
} else {
    println("No")
}

You get this error:

Playground execution failed: :33:16: error: 'UICollectionViewController' is not a subtype of 'UINavigationController' if let vc = nc as? UICollectionViewController {

but if instead you do:

var nc = UINavigationController()

if let vc = (nc as Any) as? UICollectionViewController {
    println("Yes")
} else {
    println("No")
}

it prints "No".

So I suggest trying:

extension UIViewController {

    func traverseAndFindClass<T where T : UIViewController>(T.Type) -> T? {
        var currentVC = self
        while let parentVC = currentVC.parentViewController {
            println("comparing \(parentVC) to \(T.description())")
            if let result = (parentVC as Any) as? T { // (XXX)
                return result
            }
            currentVC = parentVC
        }
        return nil
    }
}