<?php

class clonable
{
    public function __construct(...$args)
    {
         $this->args = func_get_args();
    }

    public function __clone()
    {
        return new self(...$this->args);
    }
}

class a extends clonable
{
    public function __construct($a, $b)
    {
        parent::__construct($a, $b);
        $this->a = $a;
        $this->b = $b;
    }
}

$a1 = new a(1, 2);
$a2 = clone $a1;
$a2->b = 3;

var_dump($a1, $a2);