span
可用于高性能字符串分割等
https://www.cnblogs.com/lonelyxmas/p/10171869.html
https://www.codemag.com/article/1807051/Introducing-.NET-Core-2.1-Flagship-Types-Span-T-and-Memory-T?tdsourcetag=s_pctim_aiomsg
tuple
用于方法的多返回值
https://www.cnblogs.com/lavender000/p/6916157.html
