Method demo

examples/demo.php:395–411

* @param Rock|Banana $item * @param list $rocks */

($item, array $rocks)

     * @param list<Rock> $rocks
     */
    public function demo($item, array $rocks): void
    {
        if (in_array($item, $rocks, true)) {
            $item->crush();                       // narrowed to Rock
            // MUST NOT appear: peel() (Banana only)
        } else {
            $item->peel();                        // excluded Rock → Banana
            // MUST NOT appear: crush() (Rock only)
        }

        // Guard clause with in_array
        $specimen = pickRockOrBanana();           // Rock|Banana
        if (!in_array($specimen, $rocks, true)) {
            return;
        }
        $specimen->crush();                       // narrowed to Rock after guard
    }
}