Swift Get String before Substring

Question

I have a string, this string changes constantly.

I grab a part of my string which in code can be called let mySub = "xyz"

The original string is something that is changing over time, so dont worry how I get mySub for this example lets say the string is let baseString = 123123xyz1234

How would I be able to grab a substring of everything before xyz without it being hard coded so the position of xyz can be different and the substring grabbing still works correctly?

Is performance something that should be considered? Do you only need everything before "x"? What happens if no "x" is found? — Alladinian, Jul 03 '20 at 19:07
This should give a good start: https://stackoverflow.com/q/32305891/1187415. — Martin R, Jul 03 '20 at 19:10
Concretely this: https://stackoverflow.com/a/45477831/1187415. — Martin R, Jul 03 '20 at 19:16

Omer Faruk Ozturk · Accepted Answer · 2020-07-03T21:01:14.557

2

You can find first matching range of mySub in baseString, and if found, get previous part.

let baseString: String = "123123xyz1234"
let mySub = "xyz"
if let range = baseString.range(of: mySub) {
    let beforeStr = baseString[..<range.lowerBound]
}

edited Jul 03 '20 at 21:01

answered Jul 03 '20 at 19:18

Omer Faruk Ozturk

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score 1 · Answer 2 · answered Jul 03 '20 at 20:22

You can get the lowerbound index of the range of your substring and get the substring upTo that index. If you would like to make a caseInsensitive of diacritic insensitive search you can use localizedStandardRange:

extension StringProtocol  {
    func substring<S: StringProtocol>(upTo string: S, options: String.CompareOptions = []) -> SubSequence? {
        guard let lower = range(of: string, options: options)?.lowerBound
        else { return nil }
        return self[..<lower]
    }
    func localizedStandardSubstring<S: StringProtocol>(upTo string: S, options: String.CompareOptions = []) -> SubSequence? {
        guard let lower = localizedStandardRange(of: string)?.lowerBound
        else { return nil }
        return self[..<lower]
    }
}

let string = "123123xyz1234"
if let substring = string.substring(upTo: "xyz") {
    print(substring)  // "123123\n"
}

let localized = "123123café1234"
if let substring = localized.localizedStandardSubstring(upTo: "CAFE") {
    print(substring)  // "123123\n"
}

Swift Get String before Substring

2 Answers2