Swift: Cannot figure out this crash when using safe index Extension to index into an array?

Asked Oct 02 '21 at 22:13

Active Oct 02 '21 at 22:13

Viewed 229 times

I'm using this extension to safely index into an array, which has worked well, but now and then I am seeing a crash on this line guard let priorSamplesEndDate = currentSamplesInShiftInterval[safe: indexOfCurrentSample - 1]?.endDate else { return } and cannot figure out how this could ever be out of range?

//Safe Indexing Extension
    extension Collection where Indices.Iterator.Element == Index {
       public subscript(safe index: Index) -> Iterator.Element? {
         return (startIndex <= index && index < endIndex) ? self[index] : nil
       }
    }

//usage
  if currentSamplesInShiftInterval.count > 1 {
            
            guard let indexOfCurrentSample = currentSamplesInShiftInterval.firstIndex(of: distanceSample) else {return }
            guard let priorSamplesEndDate = currentSamplesInShiftInterval[safe: indexOfCurrentSample - 1]?.endDate else { return } //crash occurs here for index out of range

}

asked Oct 02 '21 at 22:13

GarySabo

5,806
5
49
124

1

Is your array being mutated in another thread concurrently? – Paulw11 Oct 02 '21 at 22:21
@Paulw11 it is accessed and read outside of the class but is not mutated. – GarySabo Oct 02 '21 at 22:34
2

Not related to your post but I would use `indices.contains(index) ? self[index] : nil` instead – Leo Dabus Oct 02 '21 at 23:12
Btw try the implementation I posted [here](https://stackoverflow.com/a/38215613/2303865) it is much safer – Leo Dabus Oct 02 '21 at 23:17
@LeoDabus will do, thank you! – GarySabo Oct 03 '21 at 16:24

Swift: Cannot figure out this crash when using safe index Extension to index into an array?

0 Answers0