在PHP中创建子对象并将parent作为参数传递给构造

Question

When u create an child object and you want to pass a parent object as parameter on construct you can do like in the code below:

class parent {
  protected $x;
  protected $y;
  public function __construct($x, $y) {
    $this->x = $x;
    $this->y = $y;
  }
}

class child extends parent {
 protected $z;
 public function __construct($parent, $z) {
   parent::__construct($parent->x, $parent->y);
   $this->z = $z;
 }
}

but in this case i am just multiplying parent.

Is there any way to not copy parents data and append proper object? and code to look something like this:

class child extends parent {
 protected $z;
 public function __construct($parent, $z) {
   parent = $parent;
   $this->z = $z;
 }
}