Parent Object in php

is there a way to traverse an object to get the parent object data? With "parent object" I don't mean the parent class, but literally object. Here an example, in a javascripty world :-) :

$parent->test = "hello world!";

$parent->child = new B();

It would be great If I could access all the data from parent in the child object:

class B{

//I know this doesn't exists, but it's what I wanted do do
    function B(){
        $this->parent = $this->parent();
        echo $this->parent->test; //it would ouput "hello world"
    }
}

For now my solution is to pass the parent object to the child (as a reference) or to make the parent global. Do you have any better solution?

Thanks!