Swift

Regular Expression with Named Capture Groups

See more Regular Expressions Examples

Demonstrates regular expressions with named capture groups.

See the sample code below.

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

In PCRE2, named capture groups allow you to assign a name to a capturing group, making it easier to reference by name instead of number.

Syntax

(?<name>pattern)

or

(?'name'pattern)

Example

(?<first>\w+)\s+(?<last>\w+)

Applied to:

"John Smith"

Produces:

• first: John
• last: Smith

Swift

func chilkatTest() {
    var success: Bool = false

    var subject: String? = "John Smith"
    var pattern: String? = "(?<first>\\w+)\\s+(?<last>\\w+)"

    let sb = CkoStringBuilder()!
    sb.append(value: subject)

    let json = CkoJsonObject()!
    json.emitCompact = false

    var timeoutMs: Int = 2000
    var numMatches: Int = sb.regexMatch(pattern: pattern, json: json, timeoutMs: timeoutMs).intValue
    if numMatches < 0 {
        // Probably an error in the regular expression.
        // Suggestion: Use AI to help create and/or diagnose regular expressions.
        print("\(sb.lastErrorText!)")
        return
    }

    // Examine the matches:
    print("\(json.emit()!)")

    // Here is the JSON showing the matches.
    // Important:  Capture group 0 always contains the entire match — that is, the portion of the input string that matches the full regular expression.

    // {
    //   "named": {
    //     "first": 1,
    //     "last": 2
    //   },
    //   "match": [
    //     {
    //       "group": [
    //         {
    //           "cap": "John Smith",
    //           "idx": 0,
    //           "len": 10
    //         },
    //         {
    //           "cap": "John",
    //           "idx": 0,
    //           "len": 4
    //         },
    //         {
    //           "cap": "Smith",
    //           "idx": 5,
    //           "len": 5
    //         }
    //       ]
    //     }
    //   ]
    // }

    // The capture group index is obtained by looking up the name in the JSON result.
    // For example:

    json.i = json.int(of: "named.first").intValue
    print("first: \(json.string(of: "match[0].group[i].cap")!)")

    json.i = json.int(of: "named.last").intValue
    print("last: \(json.string(of: "match[0].group[i].cap")!)")

    // Output is: 

    // first: John
    // last: Smith

}