<?php
class C {
	function thisAsVariableVariable() {
		//$this;  // Uncomment to change behaviour.
		$thisName = 'this';
		var_dump($$thisName);
	}
	function thisInGetDefinedVars() {
		//$this;  // Uncomment to change behaviour.
		var_dump(get_defined_vars()); 
	}	
}
$c = new C;
$c->thisAsVariableVariable();
$c->thisInGetDefinedVars();
?>

@@Output with //$this commented out:
Notice: Undefined variable: this in %s on line 6
NULL
array(0) {
}

@@Output after uncommenting $this:
object(C)#1 (0) {
}
array(1) {
  ["this"]=>
  object(C)#1 (0) {
  }
}