Mastering RegexBuilder: A Step-by-Step Guide

Setting Up a Swift Playground

Before we begin, let’s set up a Swift playground to experiment with RegexBuilder. Create a new playground in Xcode and add the following code:

import UIKit

This imports the UIKit framework, which we’ll use later to test our regular expressions.

Using the Regex API

Before we dive into RegexBuilder, let’s take a look at the traditional Regex API. Replace the code in your playground with the following:

let text = "[email protected]"
let regex = try! NSRegularExpression(pattern: "\\d+@\\w+", options: [])
let match = regex.firstMatch(in: text, options: [], range: NSRange(location: 0, length: text.count))
print(match)

This code creates a regular expression that matches one or more digits followed by the “@” symbol and one or more word characters. The firstMatch method returns the first match in the text, which we print to the console.

Introducing RegexBuilder

Now that we’ve seen the traditional Regex API, let’s introduce RegexBuilder. RegexBuilder is a new way to write regular expressions that uses a more declarative syntax. Here’s an example of how we might rewrite the previous regular expression using RegexBuilder:

let text = "[email protected]"
let regex = Regex {
    OneOrMore(.digit)
    "@"
    OneOrMore(.word)
}
let match = try! regex.firstMatch(in: text)
print(match)

As you can see, RegexBuilder uses a more concise and readable syntax than the traditional Regex API.

Quantifiers

In RegexBuilder, quantifiers are used to specify the number of times a pattern should be matched. There are several types of quantifiers available:

• OneOrMore: Matches one or more occurrences of a pattern.
• ZeroOrMore: Matches zero or more occurrences of a pattern.
• Exactly: Matches exactly one occurrence of a pattern.

Here’s an example of how we might use these quantifiers:

let text = "[email protected]"
let regex = Regex {
    Exactly(1).digit
    "@"
    ZeroOrMore(.word)
}
let match = try! regex.firstMatch(in: text)
print(match)

Choices

In RegexBuilder, choices are used to specify multiple patterns that can be matched. There are several types of choices available:

• ChoiceOf: Matches one of several patterns.
• Either: Matches either of two patterns.

Here’s an example of how we might use these choices:

let text = "[email protected]"
let regex = Regex {
    ChoiceOf {
        Exactly(1).digit
        Exactly(1).word
    }
    "@"
    ZeroOrMore(.word)
}
let match = try! regex.firstMatch(in: text)
print(match)

Character Classes

In RegexBuilder, character classes are used to specify a set of characters that can be matched. There are several types of character classes available:

• CharacterClass: Matches a specific set of characters.
• Digit: Matches any digit.
• Word: Matches any word character.

Here’s an example of how we might use these character classes:

let text = "[email protected]"
let regex = Regex {
    CharacterClass("a-z")
    "@"
    Word
}
let match = try! regex.firstMatch(in: text)
print(match)

Currency and Date

RegexBuilder also provides built-in support for matching currency and date patterns. Here’s an example of how we might use these patterns:

let text = "The price is $123.45 and the date is 2022-12-31."
let regex = Regex {
    Currency(code: "USD", locale: Locale(identifier: "en_US"))
    Date(format: .long, locale: Locale(identifier: "en_US"), timeZone: TimeZone(identifier: "UTC")!)
}
let match = try! regex.firstMatch(in: text)
print(match)

Capturing Matched Text

Finally, let’s talk about capturing matched text. In RegexBuilder, we can capture matched text using the Capture method. Here’s an example of how we might use this method:

let text = "[email protected]"
let regex = Regex {
    Capture {
        OneOrMore(.digit)
        "@"
        OneOrMore(.word)
    }
}
let match = try! regex.firstMatch(in: text)
print(match)