public function join(array $array, string $separator = ','): string
    {
        $result = '';

        foreach ($array as $item) {
            if (is_array($item)) {
                $result .= $this->join($item, $separator) . $separator;
            } else {
                $result .= $item . $separator;
            }
        }

        $result = substr($result, 0, 0 - strlen($separator));

        return $result;
    }