Incredibly Evil Code

<?php

class ImprintingChild
{
        protected $parent;
        public function __construct()
        {
                $backtrace = debug_backtrace(true);
                $this->parent = $backtrace[1]['object'];
        }
}

class UnsuspectingParent
{
        protected $child;

        public function createChild()
        {
                $this->child = new ImprintingChild();
        }
        public function getChild()
        {
                return $this->child;
        }
}

$x = new UnsuspectingParent();
$x->createChild();
$y = $x->getChild();
var_dump($y);
/*
Output:

object(ImprintingChild)#2 (1) {
  ["parent":protected]=>
  object(UnsuspectingParent)#1 (1) {
    ["child":protected]=>
    *RECURSION*
  }
}
*/