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How to measure a string for Objective-C code

Swift version: 5.1

Paul Hudson    @twostraws   

Regular Swift code can treat strings like other kinds of sequence, so you can use its count property to read the number of characters it contains:

let str = "Hello, world"
let count = str.count

However, this falls down when you need to work with Objective-C code, for example NSRegularExpression, NSDataDetector, UITextChecker, and more – they use UTF-16 rather than Swift’s extended grapheme clusters, and so if you use count with them you’re likely to miss characters.

Instead, the correct solution is to measure your string’s length using utf16.count, like this:

let input = "This is a test with the URL https://www.hackingwithswift.com to be detected."
let detector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.link.rawValue)
let matches = detector.matches(in: input, options: [], range: NSRange(location: 0, length: input.utf16.count))

That guarantees your string’s length is reported fully when interacting with Objective-C code.

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Available from iOS 7.0

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