clone и __clone

<?php
class Address { public function __construct(public string $city) {} }
class Person {
    public function __construct(public string $name, public Address $address) {}
}
class DeepPerson extends Person {
    public function __clone() { $this->address = clone $this->address; }
}
$a = new Person('Ира', new Address('Казань'));
$b = clone $a;
$b->name = 'Оля';
$b->address->city = 'Омск';
echo $a->name, ' ', $a->address->city, "\n";

$c = new DeepPerson('Ира', new Address('Казань'));
$d = clone $c;
$d->address->city = 'Омск';
echo $c->address->city, "\n";
var_dump($a == $b, $c == new DeepPerson('Ира', new Address('Казань')));