Hm. Any can contain a nil value, but this isn't supposed to be a valid way to check for that, and I'm surprised it's working. @slavapestov, @jckarter?

This is behaving correctly, alas. `Any` is a subtype of `Any?`. This ends up invoking the `T? == _NilLiteral` overload, by wrapping the Any in an Any?, and the warning is there to tell you that this is probably not what you want.

That's what I thought at first, but then it would return false, and the originator says that it steps into the body after all.

Maybe the debug info is inaccurate (or we already fixed this)? I just tried a small repro, and it skips over the `if` body as I'd expect:

let x: Int? = nil
let y: Any = x

if y == nil {
  print("test")
}

Comment by Paul Schifferer (JIRA)

I'm using Swift 4.2.

If this is fixed in Swift 5, and a value of type Any can still contain nil, then how does one check for that?

Do you know for sure that it's executing the body, and the debugger isn't incorrectly placing the breakpoint? I'd want to verify that we don't still have a debugger bug here.

As for checking whether an `Any` contains a `nil`, what are you trying to do with the information? You can do this unfortunately rather circuitous thing to hack around the compiler trying to optimize away the Any-to-Any? check:

func isNilAny(_ value: Any) -> Bool {
  // We need this to hide the `as? Any?` cast from getting short-circuited by the type checker
  func cast<U>(_ value: Any, to: U.Type) -> U? {
    return value as? U
  }

  if let optionalValue = cast(value, to: Any?.self), // if the Any contains an Optional...
     optionalValue == nil { // ...and that optional is nil...
    return true
  }
  return false
}

It might be more constructive to ask the `Any` whether it's one of the types you're expecting it to be, or whether it conforms to a known protocol, rather than try to ask whether it's any kind of Optional at all, though.

Comment by Paul Schifferer (JIRA)

I know that I stepped into the if-body once with the debugger, as illustrated in the attached screenshot. (In the course of collecting some information to respond to your other question, I have discovered some issues with my code.) But to summarize, the code in question is attempting to populate a CKRecord by using a Mirror on an arbitrary value object (the class uses a generic for that object's type), and iterating over the Mirror's children.

The function provided in the previous comment addresses my issue, but it still feels like there should be a better way to check for nil on an Any type, since that's a valid value.