Hi,
C++20 modules seem to be a good tool to improve compile times and to hide the implementation details of the libraries.
I've been looking throught the sources of {fmt} library. Looks like the fmt library approach to C++20 modularization seems to fit Boost quite well.
I performed an analysis for Boost some months ago. Here is what I found out: - https://anarthal.github.io/cppblog/modules - https://anarthal.github.io/cppblog/modules2 And here's the discussion we had on this ML: - https://lists.boost.org/Archives/boost/2024/04/256460.php - https://lists.boost.org/Archives/boost/2024/04/256597.php TL;DR: - Modules help build times when parsing dominates. Clean builds don't gain as much as you'd expect, but re-builds are much faster. - Mixing #include <std_header> and import std causes errors on most compilers at the moment (although it should not). We were in contact with MSVC devs and the fix may take time. - Distributing modules to users so they can consume them with CMake isn't trivial. In this sense, Boost is different to fmtlib in that a) most libs are header-only and b) we have a deep dependency tree (where fmtlib is a single library). - Some core maintainers (including Peter Dimov and Rene Rivera) manifested that the amount of work required to enable modules for core libraries wasn't worth the effort. Together with point 2 above, this limits the number of libraries that can be modularized to only the ones without dependencies (e.g. Boost.Decimal). I think the biggest challenge in distributing Boost as a module is the CMake consumption part. Without solving this, we won't get anywhere. I'm happy to hear your opinion. Regards, Ruben.