https://blog.wongcw.com/2021/04/04/php-8-1%e6%96%b0%e7%89%b9%e6%80%a7%e5%85%ac%e4%bd%88%e5%a2%9e%e5%8a%a0enums%e3%80%81fsync%e5%8a%9f%e8%83%bd/