<?php
trait Timestampable
{
    public ?string $createdAt = null;

    public function touch(): void
    {
        $this->createdAt = date("Y-m-d");
    }
}

class Article
{
    use Timestampable;
    public function __construct(public string $title)
    {
    }
}

class Comment
{
    use Timestampable;
}

$a = new Article("Learning PHP");
$a->touch();
echo $a->createdAt; // today's date, e.g. 2026-07-15
?>