Basic Syntax and Style

<?php

declare(strict_types=1);

$book = ['title' => 'Kindred', 'year' => 1979];
?>
<p>
    <?= htmlspecialchars($book['title'], ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8') ?>
    (<?= $book['year'] ?>)
</p>

<p>
    Kindred    (1979)
</p>

<?php

declare(strict_types=1);

$books = ['Solaris', 'Kindred', 'The Dispossessed'];
$e = static fn (string $s): string => htmlspecialchars($s, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
?>
<?php if ($books === []): ?>
  <p>The catalogue is empty.</p>
<?php else: ?>
  <ul>
  <?php foreach ($books as $title): ?>
    <li><?= $e($title) ?></li>
  <?php endforeach; ?>
  </ul>
<?php endif; ?>

<?php

declare(strict_types=1);

$a = 1; $b = 2;            // two statements on one line: legal but discouraged
$sum = $a
     + $b;                 // one statement over two lines
echo $sum, "\n";           // 3

<?php

declare(strict_types=1);

// A single-line comment, C++ style
# A single-line comment, shell style (avoid: see below)

/*
 * A block comment. It cannot be nested:
 * the first "*" "/" sequence ends it.
 */

/**
 * A doc comment, attached to the function below.
 *
 * @param list<string> $titles
 */
function longestTitle(array $titles): ?string
{
    // A single-line comment ends at the end of the line or at the first closing tag on that line.
    return array_reduce($titles, fn (?string $carry, string $t): string => strlen($t) > strlen($carry ?? '') ? $t : $carry);
}

echo longestTitle(['Solaris', 'Kindred', 'The Dispossessed']), "\n";   // The Dispossessed

$doc = (new ReflectionFunction('longestTitle'))->getDocComment();
echo strtok($doc, "\n"), "\n";                                       // /**

<?php

declare(strict_types=1);

function shelve(string $title): string { return "Shelved: {$title}"; }

echo SHELVE('Solaris'), "\n";      // functions are case-insensitive: Shelved: Solaris

$title = 'a';
$Title = 'b';
echo $title, $Title, "\n";         // ab -- variables are case-sensitive

echo TRUE === true ? "same\n" : "different\n";   // same

<?php

declare(strict_types=1);

final class Shelf
{
    public const LIST = 'list';          // "list" is a keyword, but fine as a class constant name

    public function list(): array        // ... and as a method name
    {
        return ['Solaris', 'Kindred'];
    }

    public function new(): self { return new self(); }
}

print_r((new Shelf())->new()->list());
echo Shelf::LIST, "\n";

<?php

declare(strict_types=1);

namespace Library\Catalogue;

use DateTimeImmutable;
use InvalidArgumentException;

final class Loan
{
    public const int MAX_DAYS = 21;

    public function __construct(
        public readonly string $isbn,
        public readonly DateTimeImmutable $borrowedAt,
    ) {
    }

    public function dueAt(): DateTimeImmutable
    {
        return $this->borrowedAt->modify('+' . self::MAX_DAYS . ' days');
    }

    public function isOverdue(DateTimeImmutable $now): bool
    {
        if ($now < $this->borrowedAt) {
            throw new InvalidArgumentException('The loan cannot end before it starts.');
        }

        return $now > $this->dueAt();
    }
}

$loan = new Loan('978-0-00-000001-1', new DateTimeImmutable('2026-09-01'));
echo $loan->dueAt()->format('Y-m-d'), "\n";                                    // 2026-09-22
var_dump($loan->isOverdue(new DateTimeImmutable('2026-10-05')));               // bool(true)

<?php

declare(strict_types=1);

/**
 * Finds the books written by one author.
 *
 * @param list<array{title: string, author: string, year: int}> $books
 * @param non-empty-string $author
 *
 * @return list<string> The matching titles, in catalogue order.
 *
 * @throws InvalidArgumentException When $author is blank.
 *
 * @see https://www.php.net/manual/en/function.array-filter.php
 */
function titlesBy(array $books, string $author): array
{
    if (trim($author) === '') {
        throw new InvalidArgumentException('Author must not be blank.');
    }

    return array_values(array_map(
        fn (array $b): string => $b['title'],
        array_filter($books, fn (array $b): bool => $b['author'] === $author),
    ));
}

print_r(titlesBy([
    ['title' => 'Kindred', 'author' => 'Octavia E. Butler', 'year' => 1979],
    ['title' => 'Solaris', 'author' => 'Stanisław Lem', 'year' => 1961],
    ['title' => 'Dawn', 'author' => 'Octavia E. Butler', 'year' => 1987],
], 'Octavia E. Butler'));