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    <h3>Editing: CodePointString.php</h3>
    <textarea name="content" rows="20" cols="80">&lt;?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier &lt;fabien@symfony.com&gt;
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\String;

use Symfony\Component\String\Exception\ExceptionInterface;
use Symfony\Component\String\Exception\InvalidArgumentException;

/**
 * Represents a string of Unicode code points encoded as UTF-8.
 *
 * @author Nicolas Grekas &lt;p@tchwork.com&gt;
 * @author Hugo Hamon &lt;hugohamon@neuf.fr&gt;
 *
 * @throws ExceptionInterface
 */
class CodePointString extends AbstractUnicodeString
{
    public function __construct(string $string = '')
    {
        if ('' !== $string &amp;&amp; !preg_match('//u', $string)) {
            throw new InvalidArgumentException('Invalid UTF-8 string.');
        }

        $this-&gt;string = $string;
    }

    public function append(string ...$suffix): AbstractString
    {
        $str = clone $this;
        $str-&gt;string .= 1 &gt;= \count($suffix) ? ($suffix[0] ?? '') : implode('', $suffix);

        if (!preg_match('//u', $str-&gt;string)) {
            throw new InvalidArgumentException('Invalid UTF-8 string.');
        }

        return $str;
    }

    public function chunk(int $length = 1): array
    {
        if (1 &gt; $length) {
            throw new InvalidArgumentException('The chunk length must be greater than zero.');
        }

        if ('' === $this-&gt;string) {
            return [];
        }

        $rx = '/(';
        while (65535 &lt; $length) {
            $rx .= '.{65535}';
            $length -= 65535;
        }
        $rx .= '.{'.$length.'})/us';

        $str = clone $this;
        $chunks = [];

        foreach (preg_split($rx, $this-&gt;string, -1, \PREG_SPLIT_DELIM_CAPTURE | \PREG_SPLIT_NO_EMPTY) as $chunk) {
            $str-&gt;string = $chunk;
            $chunks[] = clone $str;
        }

        return $chunks;
    }

    public function codePointsAt(int $offset): array
    {
        $str = $offset ? $this-&gt;slice($offset, 1) : $this;

        return '' === $str-&gt;string ? [] : [mb_ord($str-&gt;string, 'UTF-8')];
    }

    public function endsWith($suffix): bool
    {
        if ($suffix instanceof AbstractString) {
            $suffix = $suffix-&gt;string;
        } elseif (\is_array($suffix) || $suffix instanceof \Traversable) {
            return parent::endsWith($suffix);
        } else {
            $suffix = (string) $suffix;
        }

        if ('' === $suffix || !preg_match('//u', $suffix)) {
            return false;
        }

        if ($this-&gt;ignoreCase) {
            return preg_match('{'.preg_quote($suffix).'$}iuD', $this-&gt;string);
        }

        return \strlen($this-&gt;string) &gt;= \strlen($suffix) &amp;&amp; 0 === substr_compare($this-&gt;string, $suffix, -\strlen($suffix));
    }

    public function equalsTo($string): bool
    {
        if ($string instanceof AbstractString) {
            $string = $string-&gt;string;
        } elseif (\is_array($string) || $string instanceof \Traversable) {
            return parent::equalsTo($string);
        } else {
            $string = (string) $string;
        }

        if ('' !== $string &amp;&amp; $this-&gt;ignoreCase) {
            return \strlen($string) === \strlen($this-&gt;string) &amp;&amp; 0 === mb_stripos($this-&gt;string, $string, 0, 'UTF-8');
        }

        return $string === $this-&gt;string;
    }

    public function indexOf($needle, int $offset = 0): ?int
    {
        if ($needle instanceof AbstractString) {
            $needle = $needle-&gt;string;
        } elseif (\is_array($needle) || $needle instanceof \Traversable) {
            return parent::indexOf($needle, $offset);
        } else {
            $needle = (string) $needle;
        }

        if ('' === $needle) {
            return null;
        }

        $i = $this-&gt;ignoreCase ? mb_stripos($this-&gt;string, $needle, $offset, 'UTF-8') : mb_strpos($this-&gt;string, $needle, $offset, 'UTF-8');

        return false === $i ? null : $i;
    }

    public function indexOfLast($needle, int $offset = 0): ?int
    {
        if ($needle instanceof AbstractString) {
            $needle = $needle-&gt;string;
        } elseif (\is_array($needle) || $needle instanceof \Traversable) {
            return parent::indexOfLast($needle, $offset);
        } else {
            $needle = (string) $needle;
        }

        if ('' === $needle) {
            return null;
        }

        $i = $this-&gt;ignoreCase ? mb_strripos($this-&gt;string, $needle, $offset, 'UTF-8') : mb_strrpos($this-&gt;string, $needle, $offset, 'UTF-8');

        return false === $i ? null : $i;
    }

    public function length(): int
    {
        return mb_strlen($this-&gt;string, 'UTF-8');
    }

    public function prepend(string ...$prefix): AbstractString
    {
        $str = clone $this;
        $str-&gt;string = (1 &gt;= \count($prefix) ? ($prefix[0] ?? '') : implode('', $prefix)).$this-&gt;string;

        if (!preg_match('//u', $str-&gt;string)) {
            throw new InvalidArgumentException('Invalid UTF-8 string.');
        }

        return $str;
    }

    public function replace(string $from, string $to): AbstractString
    {
        $str = clone $this;

        if ('' === $from || !preg_match('//u', $from)) {
            return $str;
        }

        if ('' !== $to &amp;&amp; !preg_match('//u', $to)) {
            throw new InvalidArgumentException('Invalid UTF-8 string.');
        }

        if ($this-&gt;ignoreCase) {
            $str-&gt;string = implode($to, preg_split('{'.preg_quote($from).'}iuD', $this-&gt;string));
        } else {
            $str-&gt;string = str_replace($from, $to, $this-&gt;string);
        }

        return $str;
    }

    public function slice(int $start = 0, ?int $length = null): AbstractString
    {
        $str = clone $this;
        $str-&gt;string = mb_substr($this-&gt;string, $start, $length, 'UTF-8');

        return $str;
    }

    public function splice(string $replacement, int $start = 0, ?int $length = null): AbstractString
    {
        if (!preg_match('//u', $replacement)) {
            throw new InvalidArgumentException('Invalid UTF-8 string.');
        }

        $str = clone $this;
        $start = $start ? \strlen(mb_substr($this-&gt;string, 0, $start, 'UTF-8')) : 0;
        $length = $length ? \strlen(mb_substr($this-&gt;string, $start, $length, 'UTF-8')) : $length;
        $str-&gt;string = substr_replace($this-&gt;string, $replacement, $start, $length ?? \PHP_INT_MAX);

        return $str;
    }

    public function split(string $delimiter, ?int $limit = null, ?int $flags = null): array
    {
        if (1 &gt; $limit = $limit ?? \PHP_INT_MAX) {
            throw new InvalidArgumentException('Split limit must be a positive integer.');
        }

        if ('' === $delimiter) {
            throw new InvalidArgumentException('Split delimiter is empty.');
        }

        if (null !== $flags) {
            return parent::split($delimiter.'u', $limit, $flags);
        }

        if (!preg_match('//u', $delimiter)) {
            throw new InvalidArgumentException('Split delimiter is not a valid UTF-8 string.');
        }

        $str = clone $this;
        $chunks = $this-&gt;ignoreCase
            ? preg_split('{'.preg_quote($delimiter).'}iuD', $this-&gt;string, $limit)
            : explode($delimiter, $this-&gt;string, $limit);

        foreach ($chunks as &amp;$chunk) {
            $str-&gt;string = $chunk;
            $chunk = clone $str;
        }

        return $chunks;
    }

    public function startsWith($prefix): bool
    {
        if ($prefix instanceof AbstractString) {
            $prefix = $prefix-&gt;string;
        } elseif (\is_array($prefix) || $prefix instanceof \Traversable) {
            return parent::startsWith($prefix);
        } else {
            $prefix = (string) $prefix;
        }

        if ('' === $prefix || !preg_match('//u', $prefix)) {
            return false;
        }

        if ($this-&gt;ignoreCase) {
            return 0 === mb_stripos($this-&gt;string, $prefix, 0, 'UTF-8');
        }

        return 0 === strncmp($this-&gt;string, $prefix, \strlen($prefix));
    }
}
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