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# RegexBuilder

Use an expressive domain-specific language to build regular expressions,
for operations like searching and replacing in text.

## Overview

Regular expressions, also known as regexes,
are a powerful tool for matching patterns in text.
Swift supports several ways to create a regular expression,
including from a string, as a literal, and using this DSL.
For example:

```swift
let word = OneOrMore(.word)
let emailPattern = Regex {
    Capture {
        ZeroOrMore {
            word
            "."
        }
        word
    }
    "@"
    Capture {
        word
        OneOrMore {
            "."
            word
        }
    }
}

let text = "My email is my.name@example.com."
if let match = text.firstMatch(of: emailPattern) {
    let (wholeMatch, name, domain) = match.output
    // wholeMatch is "my.name@example.com"
    // name is "my.name"
    // domain is "example.com"
}
```

## Topics

### Components

[`CharacterClass`](/documentation/RegexBuilder/CharacterClass)

A class of characters that match in a regex.

[`Anchor`](/documentation/RegexBuilder/Anchor)

A regex component that matches a specific condition at a particular position
in an input string.

[`Lookahead`](/documentation/RegexBuilder/Lookahead)

A regex component that allows a match to continue only if its contents
match at the given location.

[`NegativeLookahead`](/documentation/RegexBuilder/NegativeLookahead)

A regex component that allows a match to continue only if its contents
do not match at the given location.

[`ChoiceOf`](/documentation/RegexBuilder/ChoiceOf)

A regex component that chooses exactly one of its constituent regex
components when matching.

### Quantifiers

[`One`](/documentation/RegexBuilder/One)

A regex component that matches exactly one occurrence of its underlying
component.

[`Optionally`](/documentation/RegexBuilder/Optionally)

A regex component that matches zero or one occurrences of its underlying
component.

[`ZeroOrMore`](/documentation/RegexBuilder/ZeroOrMore)

A regex component that matches zero or more occurrences of its underlying
component.

[`OneOrMore`](/documentation/RegexBuilder/OneOrMore)

A regex component that matches one or more occurrences of its underlying
component.

[`Repeat`](/documentation/RegexBuilder/Repeat)

A regex component that matches a selectable number of occurrences of its
underlying component.

[`Local`](/documentation/RegexBuilder/Local)

A regex component that represents an atomic group.

### Captures

[`Capture`](/documentation/RegexBuilder/Capture)

A regex component that saves the matched substring, or a transformed result,
for access in a regex match.

[`TryCapture`](/documentation/RegexBuilder/TryCapture)

A regex component that attempts to transform a matched substring, saving
the result if successful and backtracking if the transformation fails.

[`Reference`](/documentation/RegexBuilder/Reference)

A reference to a captured portion of a regular expression.

### Builders

[`RegexComponentBuilder`](/documentation/RegexBuilder/RegexComponentBuilder)

A custom parameter attribute that constructs regular expressions from
closures.

[`AlternationBuilder`](/documentation/RegexBuilder/AlternationBuilder)

A custom parameter attribute that constructs regular expression alternations
from closures.


---

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