搬运工，借鉴前辈的理解，留个笔记复习
https://zhuanlan.zhihu.com/p/98785902
https://www.cnblogs.com/peixu/p/13194801.html
https://blog.csdn.net/cc__cc__/article/details/105437414
https://blog.csdn.net/claroja/article/details/108277589
https://blog.csdn.net/qq_50571974/article/details/124314082
