Swift 3 Protocol casting on Any value containing Optional

Question

Here's some strange behavior, I have a value of type Any and I wish to switch on it's protocol conformance, and when the real type of the value is optional, it does not work:

let something: Int? = 42

switch something {
case let x as Equatable: print("Yeepee! The answer is \(x)") // Here's what is matched
default: print("Boohoo!") 
}

let anything: Any = something // anything contains a Int? value

switch anything {
case let x as Equatable: print("Yeepee! The answer is \(x)")
default: print("Boohoo!")  // Here's what is matched
}

First I simply do not understand why the behavior is different, then how can I make the second switch match correctly the value, even if it's optional?

Thanks in advance.

Thank you, but unfortunately it uses reflexion API, which is currently intended to be used by Playground or debugger internally, not for production code. Moreover, the `reflect` function is not available in *Swift 3*. — Zaphod, Oct 11 '16 at 12:15
Yeah, this is really great example (one of the canonical examples in fact) of why `Any` is such a horrible type in Swift and needs to be limited as much as possible. Basically, this is a case of "if you need this, you're on the wrong road." Swift blows up constantly when faced w/ `Any` (and to a only slightly lesser extent when faced with `AnyObject`), and one of the the most subtle and pervasive versions of blowing up is when it interacts with Optional promotion to do all kinds of things you didn't expect. — Rob Napier, Oct 11 '16 at 12:48

score 0 · Answer 1 · answered Oct 11 '16 at 12:42

Thanks to @Shadow, I came up with this solution, but as I said it uses reflexion API which is not intended for production, but more for Playground or debugger:

func forceUnwrap(any:Any) -> Any {
    let mirror = Mirror(reflecting: any)

    if mirror.displayStyle != .optional {
        return any
    }

    if mirror.children.count == 0 {
        return NSNull()
    }

    let (_, some) = mirror.children.first!

    return forceUnwrap(any: some)
}

switch forceUnwrap(any:anything) {
case let x as Equatable: print("Yeepee! \(x)")
default: print("Boohoo!")
}

But if someone has a solution NOT using reflexion API, I'd be grateful.

Swift 3 Protocol casting on Any value containing Optional

1 Answers1