iOS11 から正規表現で名前付きキャプチャが使える

いまさらですが、 NSTextCheckingResult に range(withName:) なる定義が追加されていたので試してみました。

func yearMonthDay(from target: String) -> (year: Int, month: Int, day: Int)? {
    let pattern = "(?<year>\\d+)-(?<month>\\d+)-(?<day>\\d+)"
    let regex = try! NSRegularExpression(pattern: pattern, options: [])

    let nsTarget = target as NSString
    let nsRange = NSRange(location: 0, length: nsTarget.length)
    guard let result = regex.firstMatch(in: target, options: [], range: nsRange) else {
        return nil
    }
    return (
        Int(nsTarget.substring(with: result.range(withName: "year")))!,
        Int(nsTarget.substring(with: result.range(withName: "month")))!,
        Int(nsTarget.substring(with: result.range(withName: "day")))!
    )
}

print(yearMonthDay(from: "2018-4-10"))
// Optional((year: 2018, month: 4, day: 10))