Swift optimization level breaks converting NSArray to Array

Question

The following (somewhat contrived) code works when Swift Optimization Level is set to None [-Onone] (default for debug):

    let nsa = NSArray(array: ["foo", "bar"])
    let a = nsa as [String]

But the app crashes (crash log) during run-time when set to Fastest [-O] (default for release).

I luckily discovered I can work around the issue by doing this:

    let a = nsa as [AnyObject] as [String]

My question is two-fold:

Could you help me understand why this is happening?
Is there a better way to convert an NSArray to an Array?

UPDATE

This does seem to be a bug. I have not reported it to Apple. If someone else would like to take the time to do so, please do!

Side note: similar situation for converting NSMutableArray to Array: dev.eltima.com/post/96538497489/… — tybro0103
– tybro0103, Commented Dec 29, 2014 at 19:33
@HotLicks the app crashes when it gets to that code. Ummm... let me find out... please hold... — tybro0103
– tybro0103, Commented Dec 29, 2014 at 19:36
Still an issue with todays release of Xcode 6.2. Thanks a ton for the workaround you have found. In our case I found it would interestingly work when we add NSLog("%@", nsa) (to stay with your example) right behind the declaration. But as soon as that line was removed it crashed. stackoverflow.com/questions/29003323/… — udondan
– udondan, Commented Mar 12, 2015 at 11:53

Francescu · Accepted Answer · 2015-05-05 07:51:28Z

1

It seems to be fixed on Xcode Version 6.3.1 (6D1002).

And, not an answer to your original problem but as the new Swift 1.2 introduced, as is a forced cast, now replaced by more explicit as!. You should expect an NSArray to Array<T> where T != AnyObject or NSObject to crash.

You'd better use conditional cast as?. Avoid ! any time it's possible.

let nsa = NSArray(array: ["foo", "bar"])
if let a = nsa as? [String] {
    println("a \(a)")
}

answered May 5, 2015 at 7:51

Francescu

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