Consider using precompiled headers

[mkmkme]

C++ modules are not quite here yet. However, some features of C++20 already require to have header-only implementation like bitwise.hpp. Currently, bitwise.hpp is included in map.h which included in many source files. Hence, any change in map.h or bitwise.hpp causes recompilation of many source files, which is not great. Consider following:

• Use target_precompile_headers that luckily does exist in cmake>=3.16
• Replace inline function declarations in headers with non-inline declarations and inline definitions in source files, because it is totally valid
• Research a bit best practices of using pch.h to make it properly defined and used

[mkmkme]

it is totally valid

It is not. It still has to be in the file that is included.