Capture groups from string with given pattern in Swift

CaptureGroups.swift

extension String {
    func capturedGroups(withRegex pattern: String) -> [String]? {
        guard let regex = try? NSRegularExpression(pattern: pattern, options: []) else { return nil }
        let matches = regex.matches(in: self, options: [], range: NSRange(location: 0, length: count))
        guard let match = matches.first else { return nil }
        let lastRangeIndex = match.numberOfRanges - 1
        guard lastRangeIndex >= 1 else { return nil }

        var results = [String]()
        for i in 1...lastRangeIndex {
            let capturedGroupIndex = match.range(at: i)
            let matchedString = (self as NSString).substring(with: capturedGroupIndex)
            results.append(matchedString)
        }
        return results
    }
}