Extending Array with Subscript (Swift). Bug in Xcode 6 beta 7?

Does somebody have an idea on why this code doesn't compile with Xcode 6 beta 7? It must be a very stupid mistake, or compiler's bug:

enum State : UInt8 {
    case Off = 0
    case On  = 1
}

extension Array {
    subscript (index: State) -> Element {
        get { 
            let i = Int(index.toRaw())
            return self[i] 
        }
        set { 
            let i = Int(index.toRaw())
            self[i] = newValue 
        }
    }
}

class MyClass  {
    var results = [0, 7]
    func getResult(#state: State) { 
        return results[state]  // Error here: State not convertible to Int ????
    }
}

I have tried using a Dictionary [State: Int] instead of Array [Int], and copiler gives also error. Thanks!