Is this not valid in Swift? Tried on Xcode 7b6

hang.swift

protocol Stack {
    typealias Element
    
    mutating func push(value: Element)
    mutating func pop() -> Element?
}

struct ArrayStack<T>: Stack {
....
}

extension Stack where Self: ArrayLiteralConvertible  {
    
    init(arrayLiteral elements: Self.Element...) {
        self.init()
        print("array literal init")
        for value in elements {
            push(value)
        }
    }
    
}

extension ArrayStack: ArrayLiteralConvertible {}
print("before")
var tin: ArrayStack = [1, 2, 3]
print("after") // this never gets called.