[will4274]

Well, the standard says you can, but it doesn't actually work in practice in msvc, which is the only compiler that's supported modules for over a year.

[feelamee]

gcc and clang implemented them too, but partialy.

My comment about this absolutely wrong point:

> all of your code need to use modules

With all three major compilers you can right now use modules and at the same time include some other dependencies.