RegEx

RegEx is a thin NSRegularExpression wrapper for easier regular expression testing, data extraction, and replacement in Swift.

Features

Test if a string matches the expression with


    test()

Determine the number of matches in a string with


    numberOfMatches(in:)

Retrieve all matches in a string with


    matches(in:)

Retrieve the first match without processing all matches with


    firstMatch(in:)

Efficiently iterate over matches with


    iterator()

and


    next()

Replace matches with a template (including capture groups)

Replace matches one by one with custom replacement logic in a closure

The resulting Match structure contains the full match , any captured groups , and corresponding Swift string ranges .

By using Range<String.Index> and Substring , RegEx.Match is able to return all this information without duplicating data from the input string 👏

Usage

Given a string:

let str = "16^32=2^128"

Define an expression, for example to identify exponent notation ( ^ ) while capturing exponent values:

let expression = "\\d+\\^(\\d+)"

Use the regular expression:

let regex = try RegEx(pattern: expression)
regex.test(str) // true
regex.numberOfMatches(in: str) // 2
let first = regex.firstMatch(in: str) // 1 match with 1 captured group
first?.values // ["16^32", "32"] 
let matches = regex.matches(in: str) // 2 matches with 1 captured group each
matches[0].values // ["16^32", "32"] 
matches[1].values // ["2^128", "128"]

Iterate over matches

let iterator = regex.iterator(for: str) // Iterate over matches one by one
iterator.next()?.values // ["16^32", "32"] 
iterator.next()?.values // ["2^128", "128"]
iterator.next()         // nil

Replacement with Template

let regex = try RegEx(pattern: #"(\d)(\d)"#)
let result = regex.replaceMatches(in: "1234", withTemplate: "$2$1")
// result: 2143

Replacement with Custom Logic

let regex = try RegEx(pattern: #"(\w+)\b"#)
let result = regex.replaceMatches(in: "Hello world!")  { match in 
    let value = String(match.values[0] ?? "")
    return String(value.reversed())
// result: olleH dlrow!

Installation

No frameworks, just copy and paste!

public class RegEx {
    private let regex: NSRegularExpression
    public init(pattern: String, options: NSRegularExpression.Options = []) throws {
        regex = try NSRegularExpression(pattern: pattern, options: options)
    public struct Match {
        public let values: [Substring?]
        public let ranges: [Range<String.Index>?]
    public func numberOfMatches(in string: String, from index: String.Index? = nil) -> Int {
        let startIndex = index ?? string.startIndex
        let range = NSRange(startIndex..., in: string)
        return regex.numberOfMatches(in: string, range: range)
    public func firstMatch(in string: String, from index: String.Index? = nil) -> Match? {
        let startIndex = index ?? string.startIndex
        let range = NSRange(startIndex..., in: string)
        let result = regex.firstMatch(in: string, range: range)
        return result.flatMap { map(result: $0, in: string) }
    public func matches(in string: String, from index: String.Index? = nil) -> [Match] {
        let startIndex = index ?? string.startIndex
        let range = NSRange(startIndex..., in: string)
        let results = regex.matches(in: string, range: range)
        return results.map { map(result: $0, in: string) }
    public func test(_ string: String) -> Bool {
        return firstMatch(in: string) != nil
    func map(result: NSTextCheckingResult, in string: String) -> Match {
        let ranges = (0..<result.numberOfRanges).map { index in
            Range(result.range(at: index), in: string)
        let substrings = ranges.map { $0.flatMap { string[$0] }}
        return Match(values: substrings, ranges: ranges)
extension RegEx {
    public class Iterator: IteratorProtocol {
        let regex: RegEx
        let string: String
        var current: RegEx.Match?
        init(regex: RegEx, string: String) {
            self.regex = regex
            self.string = string
            current = regex.firstMatch(in: string)
        public func next() -> RegEx.Match? {
            defer {
                current = current.flatMap {
                    let index = $0.ranges[0]?.upperBound
                    return self.regex.firstMatch(in: self.string, from: index)
            return current
    public func iterator(for string: String) -> Iterator {
        return Iterator(regex: self, string: string)
Swift Package Manager
Actually, I love unit tests, so I made this repo a Swift package that can be imported and used with
Swift Package Manager.
Add the following code to your Package.swift :
dependencies: [
    .package(url: "https://github.com/eneko/RegEx.git", from: "0.1.0")
targets: {
    .target(name: "YourTarget", dependencies: ["RegEx"])
Unit Tests
If curious, you can run the tests with $ swift test or $ swift test --parallel.