NSRange: Crash when using index with strings containing special characters

Using Swift
1

I try to build a range in a string containing german umlauts (e. g. ä,ö,ü).

import Foundation

let testString = NSString("Wä") as String
let range = NSRange(testString.startIndex..<testString.endIndex, in: "Wäsche")

This example crashes with a fatal error with no further information printed on the console. My debugger halts with
EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0).

When I replace the umlauts with regular ascii characters, it works:
let range = NSRange(testString.startIndex..<testString.endIndex, in: "Wasche")
It also works when I don't use NSString.

The crash first occurred after updating to the new Xcode version.
Xcode 10.2
Build version 10E125

I'm not sure if I made a mistake here or it's a bug. Maybe this has something to do with the change in string encodings?

2

You're using indexes from one string on another string. Indexes valid in one string don't have to be valid in a different string (and collections in general)
If you use the same string there is no error

let testString = NSString("Wä") as String
let range = NSRange(testString.startIndex..<testString.endIndex, in: testString)
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