test.php

<?php
class A {
        public $prop = "x";
        function foo() {
                var_dump("A");
                return $this->prop;
        }
        function bar() {
                $x = $this->foo();
                var_dump(str_repeat($x,5));
        }
}
class B extends A {
        function &foo() {
                var_dump("B");
                return $this->prop;
        }
}
$b = new B;
$b->bar();