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ios - Downcast from Any to a protocol

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
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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


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