public static function set(string $fileName, array $content)
    {
        try {
            $json = Yaml::dump($content, 2);
            if (file_put_contents($fileName, $json) === false) {
                throw new FileNotWritable('can\'t write to "' . $fileName . '"');
            }
        } catch (DumpException $e) {
            throw new BadUse('Config::set() content parameter can\'t be dump to YAML');
        }
        self::$files[$fileName] = $content;
    }