### Installation

Source: https://github.com/composer/pcre/blob/main/README.md

Installs the latest version of the composer/pcre library using Composer.

```bash
composer require composer/pcre
```

--------------------------------

### Regex Replacement Examples

Source: https://github.com/composer/pcre/blob/main/README.md

Demonstrates various ways to use the Regex::replace and Regex::replaceCallback methods for string manipulation using regular expressions. Includes simple replacement, replacement with a callback function, and replacement using an array of callbacks.

```PHP
$newString = Regex::replace('{fo+}', 'bar', $string)->result;
$newString = Regex::replaceCallback('{fo+}', function ($match) { return strtoupper($match[0]); }, $string)->result;
$newString = Regex::replaceCallbackArray(['{fo+}' => fn ($match) => strtoupper($match[0])], $string)->result;
```

--------------------------------

### Basic Usage Comparison

Source: https://github.com/composer/pcre/blob/main/README.md

Compares the traditional usage of PHP's preg_* functions with the type-safe alternatives provided by the Composer PCRE library's Preg class.

```php
use Composer\Pcre\Preg;

// Traditional usage:
// if (preg_match('{fo+}', $string, $matches)) { ... }
// if (preg_match('{fo+}', $string, $matches, PREG_OFFSET_CAPTURE)) { ... }
// if (preg_match_all('{fo+}', $string, $matches)) { ... }
// $newString = preg_replace('{fo+}', 'bar', $string);
// $newString = preg_replace_callback('{fo+}', function ($match) { return strtoupper($match[0]); }, $string);
// $newString = preg_replace_callback_array(['{fo+}' => fn ($match) => strtoupper($match[0])], $string);
// $filtered = preg_grep('{[a-z]}', $elements);
// $array = preg_split('{[a-z]+}', $string);

// Composer PCRE library usage:
if (Preg::match('{fo+}', $string, $matches)) { ... }
if (Preg::matchWithOffsets('{fo+}', $string, $matches)) { ... }
if (Preg::matchAll('{fo+}', $string, $matches)) { ... }
$newString = Preg::replace('{fo+}', 'bar', $string);
$newString = Preg::replaceCallback('{fo+}', function ($match) { return strtoupper($match[0]); }, $string);
$newString = Preg::replaceCallbackArray(['{fo+}' => fn ($match) => strtoupper($match[0])], $string);
$filtered = Preg::grep('{[a-z]}', $elements);
$array = Preg::split('{[a-z]+}', $string);
```

--------------------------------

### Boolean Match Methods

Source: https://github.com/composer/pcre/blob/main/README.md

Demonstrates the use of `isMatch` and `isMatchAll` methods from the Composer PCRE library's Preg class, which return a boolean indicating if a match occurred.

```php
use Composer\Pcre\Preg;

if (Preg::isMatch('{fo+}', $string, $matches)) // bool
if (Preg::isMatchAll('{fo+}', $string, $matches)) // bool
```

--------------------------------

### Regex Class Usage

Source: https://github.com/composer/pcre/blob/main/README.md

Showcases the `Regex` class from the Composer PCRE library, which provides result objects for match operations, offering a more verbose but structured approach.

```php
use Composer\Pcre\Regex;

// this is useful when you are just interested in knowing if something matched
// as it returns a bool instead of int(1/0) for match
$bool = Regex::isMatch('{fo+}', $string);

$result = Regex::match('{fo+}', $string);
if ($result->matched) { something($result->matches); }

$result = Regex::matchWithOffsets('{fo+}', $string);
if ($result->matched) { something($result->matches); }

$result = Regex::matchAll('{fo+}', $string);
if ($result->matched && $result->count > 3) { something($result->matches); }
```

--------------------------------

### Strict Groups Match Methods

Source: https://github.com/composer/pcre/blob/main/README.md

Illustrates the usage of `matchStrictGroups` and `matchAllStrictGroups` from the Composer PCRE library's Preg class, ensuring match groups are always present and non-nullable.

```php
use Composer\Pcre\Preg;

// $matches is guaranteed to be an array of strings, if a subpattern does not match and produces a null it will throw
if (Preg::matchStrictGroups('{fo+}', $string, $matches))
if (Preg::matchAllStrictGroups('{fo+}', $string, $matches))
```

--------------------------------

### PREG_UNMATCHED_AS_NULL Behavior Comparison

Source: https://github.com/composer/pcre/blob/main/README.md

Illustrates the difference in match results when using PREG_UNMATCHED_AS_NULL compared to not using the flag. This highlights the library's consistent use of this flag for predictable and safer match outcomes.

```PHP
preg_match('/(a)(b)*(c)(d)*/', 'ac', $matches, $flags);

---

| no flag | PREG_UNMATCHED_AS_NULL |
| --- | --- |
| array (size=4)              | array (size=5) |
| 0 => string 'ac' (length=2) |   0 => string 'ac' (length=2) |
| 1 => string 'a' (length=1)  |   1 => string 'a' (length=1) |
| 2 => string '' (length=0)   |   2 => null |
| 3 => string 'c' (length=1)  |   3 => string 'c' (length=1) |
|                             |   4 => null |
```

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