public function setBase($base)
    {
        if (is_int($base) === true && $base >= 0) {
            $this->base = $base;
        } else {
            $msg = "The 'base' argument must be a positive (>= 0) integer value, '" . gettype($base) . "' given.";
            throw new InvalidArgumentException($msg);
        }
    }