You can unset superglobals like $GLOBALS, $_GET etc., but causing an unususal behavior (as of PHP 5.3.3).
1) unsetting of superglobals is done globally, i.e. unsetting inside the function affects GLOBALLY.
2) Recreation of unset'ed superglobals can be done (recreated valiables are superglobals), but original functionality (in $GLOBALS, $_SESSION ...) has lost.
<?php
function foo(){
unset($GLOBALS);
}
function bar(){
var_dump($GLOBALS);
}
foo();
bar(); //issues E_NOTICE ($GLOBALS not defined)
$GLOBALS=3;
bar(); //displays int(3)
?>