You learned nothing because the extent of your knowledge tends to be rather superficial when it comes to C++. Office does not use C++ modules, what Office did

You learned nothing because the extent of your knowledge tends to be rather superficial when it comes to C++. Office does not use C++ modules, what Office did was make use of a non-standard MSVC feature [1] which reinterprets #include preprocessor directives as header units. Absolutely no changes to source code is needed to make use of this compiler feature. This is not the same as using C++20 modules which would require an absolutely astronomical amount of effort to do. In the future, read more than just the headline of a blog post if you wish to actually understand a topic well enough to converse in it. [1] https://learn.microsoft.com/en-us/cpp/build/reference/translateinclude?view=msvc-170 https://learn.microsoft.com/en-us/cpp/build/reference/transl...