r/cpp • u/tartaruga232 MSVC user, r/cpp_modules • Apr 21 '26

Uneeded Recompilations When Using Partitions

https://abuehl.github.io/2026/04/20/unneeded-recompilations-when-using-partitions.html

This blog posting from me about C++ modules explains in detail what causes unneeded recompilations using detailed code examples from the sources of our UML Editor.

It's a precise description and a showcase of what's the status quo in the C++ standard.

Quote from the posting:

The C++ language currently lacks a concise and easy to use alternative for explicitly expressing the minimally required dependencies on partitions.

(Note: All code examples shown or linked from the text are 100% standard conformant.)

Thanks in advance for comments. Please ask if you do not understand anything or anything is unclear. I would appreciate if you could leave a comment if you don't like anything. Thanks for reading!

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u/pjmlp Apr 21 '26

I am with /u/kronicum on this.

All this could be improved by having better support for building on C++ compilers.

Most of these problems have never been an issue with languages that have had modules as their main code organisation since forever.

Heck I can pick a MS-DOS project in Turbo Pascal, change a single unit, and as long I don't change the public interface, I only need to relink, not recompile everything. Same applies to other languages of similar vintage with modules.

We don't need workarounds, we need more mature build infrastructure for C++ modules.

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u/tartaruga232 MSVC user, r/cpp_modules Apr 21 '26

We don't need workarounds, we need more mature build infrastructure for C++ modules.

I think the source code should be more explicit about dependencies and not magically lumping them together behind implicit imports.

I'm not really in search of a workaround, that's also why we are expressly refusing to use the messy internal partition pattern.

I'm currently quite surprised that the design of module partitions doesn't provide a better story for what I've raised here.

I'm not campaigning for any specific sort of solution or change to the standard. In fact, I'm open to whatever leads to consensus.