Is it possible to detect a reference at runtime in Swift 4?

Asked Feb 12 '18 at 22:11

Active Feb 12 '18 at 22:21

Viewed 39 times

Take the following code…

func f(p: Any) {
}

Can we know at runtime whether p is a reference or a value?

Now, to head off at the pass those who will ask, "Why, young Padawan, do you want to know this?" Well, it is a part of my further investigations into the Swift language.

asked Feb 12 '18 at 22:11

Gregory Higley

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Depends what you mean by reference; do you just mean whether `p` is a class instance? If so, you want `type(of: p) is AnyClass`, see https://stackoverflow.com/q/39184911/2976878. – Hamish Feb 12 '18 at 22:23
@Hamish That's right. Why don't you write it up as an answer? – Gregory Higley Feb 12 '18 at 22:25
Well aware of `type(of:)`. The secret sauce I was missing—obvious in hindsight—is `type(of: x) is AnyClass`. – Gregory Higley Feb 12 '18 at 22:28
@Hamish Doesn't that fail for ObjC bridged types? IIRC, `type(of: someStr) is AnyClass)` will be `true` because `String` would bridge to `NSString` – Alexander Feb 12 '18 at 22:29
@Alexander I just tested that in the REPL and it did _not_ return true for a string. – Gregory Higley Feb 12 '18 at 22:29
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@Alexander No, that'll be false because metatypes don't bridge – Hamish Feb 12 '18 at 22:31
@GregoryHigley Import foundation first – Alexander Feb 12 '18 at 22:31
@Hamish Oh, interesting – Alexander Feb 12 '18 at 22:31
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(after `import foundation`) `someStr is AnyObject // => true`, `type(of: someStr) is AnyObject // => false`. Checks out – Alexander Feb 12 '18 at 22:32
Consider using `Mirror` - you can identify whether an `Any` is a class or not... I added my answer to the "duplicate" question, as I can no longer add it here. – Grimxn Feb 12 '18 at 22:38

Is it possible to detect a reference at runtime in Swift 4?

0 Answers0