Description:
------------
class A {
    public function test() {
        var_dump($this);
        $this = 'oh, mygod';
        var_dump($this);
    }
}
$a = new A;
$a->test();

Fatal error: Cannot re-assign $this in D:\www\testthis.php on line 13


Reproduce code:
---------------
class A {
    public function test($arr) {
        var_dump($this);
        extract($arr);
        var_dump($this);
    }
}
$a = new A;
$arr['this'] = 'abc';
$a->test($arr);



Expected result:
----------------
Fatal error: Cannot re-assign $this in D:\www\testthis.php on line 13


Actual result:
--------------
it's ok!