public func with<T>(_ initial: T, update: (inout T) throws -> Void) rethrows -> T {
    var copy = initial
    try update(&copy)
    return copy
}

public func with<T: AnyObject>(_ object: T, update: (T) throws -> Void) rethrows -> T {
    try update(object)
    return object
}

let x = with(1) {
    $0 += 2
    $0 *= 5
    $0 -= 1
}

final class Thing {
    var name: String = ""
    var position: (Int, Int) = (0, 0)
}

let y = with(Thing()) { // Ambiguous use of `with(_:update:)`
    $0.name = "Goblin Bandit"
    $0.position = (13, 2)
}