String, substring, Range, NSRange in Swift 4

Question

I am using the following code to get a String substring from an NSRange:

func substring(with nsrange: NSRange) -> String? {
    guard let range = Range.init(nsrange)
        else { return nil }
    let start = UTF16Index(range.lowerBound)
    let end = UTF16Index(range.upperBound)
    return String(utf16[start..<end])
}

(via: https://mjtsai.com/blog/2016/12/19/nsregularexpression-and-swift/)

When I compile with Swift 4 (Xcode 9b4), I get the following errors for the two lines that declare start and end:

'init' is unavailable
'init' was obsoleted in Swift 4.0

I am confused, since I am not using an init.

How can I fix this?

Charles Srstka · Accepted Answer · 2017-08-01 23:54:02Z

33

Use Range(_, in:) to convert an NSRange to a Range in Swift 4.

extension String {
    func substring(with nsrange: NSRange) -> Substring? {
        guard let range = Range(nsrange, in: self) else { return nil }
        return self[range]
    }
}

answered Aug 1, 2017 at 23:54

Charles Srstka

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4 Comments

koen Over a year ago

Xcode forces me to fix the code as follows:

func substring(with nsrange: NSRange) -> String? {         guard let range = Range(nsrange, in: self) else { return nil }         return String(self[range])     }

Charles Srstka Over a year ago

If you make the function return a Substring instead of a String, you won't have to convert the result.

koen Over a year ago

Ah, I didn't realize Substring is a type, I thought it was a typo.

Charles Srstka Over a year ago

Substring is a slice type. What that means is that it holds a reference to the original string, as well as the range that the substring represents. The advantage of a slice is that you don't have to make a copy of the data the way you would if you were returning a new String, so performance is better.

Nathan Tuggy · Accepted Answer · 2017-09-21 05:20:42Z

5

With Swift 4 we can get substrings this way.

Substring from index

let originStr = "Test"
let offset = 1
let str = String(originStr.suffix(from: String.Index.init(encodedOffset: offset)))

Substring to index

let originStr = "Test"
let offset = 1
String(self.prefix(index))

edited Sep 21, 2017 at 5:20

Nathan Tuggy

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answered Sep 21, 2017 at 5:03

Nguyen Van Dung

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2 Comments

Peter Wiley Over a year ago

Does that second example need some editing? Should index be offset

koen Over a year ago

Also, it's not an answer to the question

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