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.