[PHP] Base64 UID

$charset = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_";

function uyid (&$charset, int $length = 11) : string {
    $id = "";
    for($i = 0; $i < $length; $i++) {
        $id .= $charset[mt_rand(0, strlen($charset) - 1)];
    }
    return $id;
}

print_r(uyid($charset, 11));