optimizestatic const，more cplusplus and complire detect error

[jiapengwen]

No description provided.

[chenshuo]

Why is this necessary? What's the benefit?

[jiapengwen]

constexpr variable is guaranteed to have a value available at compile time. whereas static const members or const variable could either mean a compile time value or a runtime value. Typing constexpr express your intent of a compile time value in a much more explicit way than const.

One more thing, in C++17, constexpr static data member variables will be inline too. That means you can omit the out of line definition of static constexpr variables, but not static const.

[jiapengwen]

constexpr is more c++