Accessing GET and POST by reference

Question

I learned how to access by reference in another answer on stackoverflow, but cannot find it again. Anyways, is the following method unsafe or at all unreliable?

protected function checkVar($requestType, $varname, $checkIfNumber = false)
{
    switch($requestType)
    {
        case 'GET':
            $sg = &$_GET;
            break;
        case 'POST':
            $sg = &$_POST;
            break;
        default:
            throw new Exception('Variable `$requestType` is not `GET` or `POST` in AController::checkVar().');
    }

    if(!isset($sg[$varname])) {
        throw new Exception("$requestType variable [$varname] is not set in AController::checkVar().");
    } else if(empty($sg[$varname])) {
        throw new Exception("$requestType variable [$varname] is empty in AController::checkVar().");
    } else  if($checkIfNumber) {
        if(!ctype_digit($sg[$varname])) {
            throw new Exception("$requestType variable [$varname] is not a number in AController::checkVar().");
        }
    }   

    return $sg[$varname];
}

Answer 1

That's why we have the $_REQUEST superglobal.

protected function checkVar($varname, $checkIfNumber = false)
{
    if(!isset($_REQUEST[$varname])) {
        throw new Exception("variable [$varname] is not set in AController::checkVar().");
    } else if(empty($_REQUEST[$varname])) {
        throw new Exception("variable [$varname] is empty in AController::checkVar().");
    } else  if($checkIfNumber) {
        if(!ctype_digit($_REQUEST[$varname])) {
            throw new Exception("variable [$varname] is not a number in AController::checkVar().");
        }
    }   

    return $_REQUEST[$varname];
}

I know it's not strictly the same thing, but IMHO it's good enough.

Answer 2

This is not how you should use references. A 'copy' operation is actually cheaper as long as the values don't change, and there is no reference needed here (especially as you're not returning by reference, but actually making a copy). The only thing references in this point of the code can do is cause obscure errors later on which can be quite hard to track down.