infinite hang in swift

fun.swift

public class Promise<T> {
}

/// These are basically promises that won't terminate until they hit the end
public enum MoreOrEnd<T> {
    public typealias ValueTuple = (T, Promise<MoreOrEnd<T>>)
    case More(ValueTuple)
    case End
}

/// Constructing this will hang
Promise<MoreOrEnd<Int>>()