C++20

Big Four:
Concept:解决模板
Coroutines:解决异步
Ranges：STL高级
Modules：解决头文件导入

Core Languages:
三路比较；location, consteval, constinit,
constexpr virtual function; volatile,

Library:
span, format, date, zone;

Concurrency:
atomic_ref, jthread, atomic<shared_ptr>, atomic<weak_ptr>

C++20 最新进展：加入模块化和协程，进入特性冻结阶段：https://www.oschina.net/news/104653/201902-kona-iso-c-committee-trip-report-c20?p=3