public static function flatten(array $array)
    {
        $out = [];

        foreach (new RecursiveIteratorIterator(new RecursiveArrayIterator($array)) as $key => $item) {
            if (is_int($key)) {
                $out[] = $item;
            } else {
                $out[$key] = $item;
            }
        }

        return $out;
    }