Is initializing a superglobal by PHP codes a right thing?

Question

Here is my code:

    $order_newest = $order_votes = $order_featured = $order_frequent = '';

    if ( isset($_GET['o']) || isset($_COOKIE['qanda_questions_order']) ) {

        // To read from the cookie
        if ( !isset($_GET['o']) ) {
            $_GET['o'] = $_COOKIE['qanda_questions_order'];
        } else {
            setcookie("qanda_questions_order", $_GET['o'], 2147483647);
        }

        switch ($_GET['o']) {
            case 'newest':
                $order_newest = 'order_active';
                break;
            case 'votes':
                $order_votes = 'order_active';
                break;
            case 'featured':
                $order_featured = 'order_active';
                break;  
            case 'frequent':
                $order_frequent = 'order_active';
                break;                                          
            default:
                $order_newest = 'order_active';
                break;
        }

    } else {
        $order_newest = 'order_active';
    }

As you see, I've initialized a supergobal on this line:

$_GET['o'] = $_COOKIE['qanda_questions_order'];

Is doing that a right thing? Or only should supergobals be used as passed parameters in the URL (get method) ?

Also can I write this logic more better? (seems Unprofessional to me a little bit)

Answer 1

Opinions vary, but in my opinion it is really bad practice to modify superglobals that are pre-filled by PHP. I always treat them as "read-only" variables (with the exception of $_SESSION) myself, even though there's nothing stopping you from writing to them. I would personally use a variable for this:

if (isset($_GET['o']) || isset($_COOKIE['qanda_questions_order'])) {
    $order = isset($_GET['o']) ? $_GET['o'] : $_COOKIE['qanda_questions_order'];
    setcookie("qanda_questions_order", $order, 2147483647);

    switch ($order) {
       // etc.
    }
}