ios - Downcast from Any to a protocol

Question

I have the following code. How can I resolve the error in the last line?

protocol Animal {
    func walk()
}

struct Cat: Animal {
    func walk() {}

    init() { }
}

var obj: Any = Cat()
var cat = obj as Animal // ERROR: cannot downcast from Any to unrelated type Animal

Answer 1

Update: This has been fixed in Swift 1.2+ (Xcode 6.3+). The Xcode 6.3 beta release notes say:

Dynamic casts (“as!", “as?" and “is”) now work with Swift protocol types, so long as they have no associated types.

---

You can only check for protocol conformance (which includes is, as, and as?) with an @objc protocol. Animal is not @objc.

See the Checking for Protocol Conformance section of the Swift book.

NOTE

You can check for protocol conformance only if your protocol is marked with the @objc attribute