Some libraries, such as fmt, ship their module sources at install time. This approach is problematic for several reasons:
If a library is developed using a modules-only approach (i.e., no headers), this forces the library to declare and ship every API in module source files. That largely defeats the purpose of modules: you end up maintaining two parallel representations of the same interface—something we are already painfully familiar with from the header/source model.
It is often argued that pcm files are unstable. But does that actually matter? Operating system packages should not rely on C++ APIs directly anyway, and how a package builds its internal dependencies is irrelevant to consumers. In a sane world, everything except
libc and user-mode drivers would be statically linked. This is exactly the approach taken by many other system-level languages.I believe pcm files should be the primary distribution format for C++ module dependencies, and consumers should be aware of the compiler flags used to build those dependencies. Shipping sources is simply re-introducing headers in a more awkward form—it’s just doing headers again, but worse
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