Classes, Objects & Constructor Promotion

<?php
declare(strict_types=1);

// ── Classic class (PHP 7 style — verbose) ──────────────────────
class PostOld {
    private int    $id;
    private string $title;
    private string $author;
    private float  $price;

    public function __construct(int $id, string $title, string $author, float $price) {
        $this->id     = $id;
        $this->title  = $title;
        $this->author = $author;
        $this->price  = $price;
    }
    // getters...
}

// ── Constructor property promotion (PHP 8.0+) — same result, less code ──
class Post {
    public function __construct(
        private readonly int    $id,
        private string          $title,
        private string          $author,
        private string          $slug,
        private string          $content   = "",
        private bool            $published = false,
        private ?DateTimeImmutable $publishedAt = null,
    ) {}

    // ── Getters (no setters for readonly/immutable design) ────────
    public function getId(): int    { return $this->id; }
    public function getTitle(): string { return $this->title; }
    public function getSlug(): string  { return $this->slug; }
    public function isPublished(): bool { return $this->published; }

    // ── Setters return new instance — immutable pattern ──────────
    public function withTitle(string $title): static {
        $clone = clone $this;
        $clone->title = $title;
        return $clone;
    }

    public function publish(): static {
        $clone = clone $this;
        $clone->published   = true;
        $clone->publishedAt = new DateTimeImmutable("now", new DateTimeZone("UTC"));
        return $clone;
    }

    // ── toString ────────────────────────────────────────────────
    public function __toString(): string {
        return sprintf("[Post #%d] %s by %s", $this->id, $this->title, $this->author);
    }

    // ── toArray — useful for JSON output ─────────────────────────
    public function toArray(): array {
        return [
            "id"           => $this->id,
            "title"        => $this->title,
            "slug"         => $this->slug,
            "author"       => $this->author,
            "published"    => $this->published,
            "published_at" => $this->publishedAt?->format("c"),
        ];
    }
}

// Usage
$post = new Post(1, "PHP Basics", "Alice", "php-basics");
echo $post;    // [Post #1] PHP Basics by Alice

$published = $post->publish();   // original unchanged
var_dump($post->isPublished());      // false
var_dump($published->isPublished()); // true

echo json_encode($post->toArray(), JSON_PRETTY_PRINT);