How can you mark a method that it is fatal, like `fatalError`?

Question

We have a special logging function that represents a particular type of crash, and as such, internally it calls fatalError. However, unlike fatalError, when we use it in a guard statement, it still complains we haven't exited the scope of the guard.

I checked the source code and fatalError returns -> Never so I tried that, but that didn't work either. I also didn't see any attributes applied to it that may be telling the compiler 'this is the end of the road'.

So is it possible to have your own fatalError-like method?

func myFatalError(memberName:String = #function) -> Never {
    let message = "Failed in \(memberName)" 
    NSLog(message)
    fatalError(message)
}

Your method works when I try it in a `guard` statement. What specifically is happening when you try it? — Charles Srstka, Mar 17 '18 at 16:04
@CharlesSrstka mine won’t even compile. Lemme try cleaning the project, derived data,, etc. — Mark A. Donohoe, Mar 17 '18 at 16:05
(Unrelated to this question, but note that using anything but a string literal as the format argument of NSLog is unsafe, better use `NSLog("Failed in %s", memberName)` ) — Martin R, Mar 17 '18 at 18:35
Good to know! This was just dummy code I typed here in the window. Do you have more information on why that is unsafe? — Mark A. Donohoe, Mar 17 '18 at 19:59
@MarqueIV: See https://stackoverflow.com/a/35336296/1187415 for an example. — Martin R, Mar 17 '18 at 20:04
Yep! Was a problem with Xcode. It was showing an error, but restarting it made it go away. Can someone here post an answer (or close this) so I can mark it as answered? — Mark A. Donohoe, Mar 18 '18 at 07:42

score 0 · Accepted Answer · answered Mar 18 '18 at 07:41

0

As pointed out by others, the issue was something on my machine specifically. The following (returning 'Never') works as expected.

func myFatalError() -> Never {
    print("Doing something fatal")
}

answered Mar 18 '18 at 07:41

Mark A. Donohoe

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How can you mark a method that it is fatal, like `fatalError`?

1 Answers1