Comment by StephenHerlihyy | Hacker News Reader

Comment by StephenHerlihyy | Hacker News Reader

StephenHerlihyy

Modules provide more than just speed. Compile time benefits are great and the article is right about build-time bloat being the bane of every developer. But modules serve a deeper purpose.

Explicit sub-unit encapsulation. True isolation. No more weird forward declarations, endlessly nested ifdef guards, or insane header dependency graphs. Things just exist as they are separate, atomic, deterministic and reliable.

Modules probably need a revision, and yes, adoption has been slow, but once you start using modules you will never go back. The clarity of explicitly declared interfaces and the freedom from header hell fundamentally changes how you think about organizing C++ code.

Start a new project with modules if you don’t believe me. Try them. That is the largest barrier right now - downstream use. They are not supported because they are not used and they are not used because they are not well supported. But once you use them you will start to eagerly await every new compiler release in hopes of them receiving the attention they deserve.

Use a feature that doesn't really work, after so many years, hoping compilers will actually make it work if people use it - seems like a disastrous plan. People have tried to use modules, and have generally found that they fail, and have dumped them.

It's unlikely at this point modules in their current form will ever be anything but a legacy feature in C++. Maybe someday a new implementation will arise, just like noexcept replaced the failed "throws" declaration.

Or a more relevant example: export templates.

Thing is (correct.me if Im wrong), that if you use modules, all of your code need to use modules (e.g. you cant have mixed #include <vector> and import <vector>; in your project). Which rules out a lot of 3rd party code you might want to depend on.

you wrong You can simply use modules with includes. If you will #include vector inside your purview then you will just get a copy of the vector in each translation unit. Not good, but works. On the other hand. If you include a vector inside the global module fragment, then the number of definitions will be actually 1, even if you include it twice in different modules.

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.

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.

Not sure why you are getting downvoted, but this alone would make me switch (Still waiting for Qt moc support):

> No more weird forward declarations

We c++ devs just have collectively accepted that this hack is still totally ok in the year 2025, just to improve build times.

The only thing that forward declaration buys you is avoiding to include a header, which is not that expensive in C, but thanks to templates something as innocent as including a header can become infinitely expensive in C++.

Forward declaration breaks dependency chains so that you don't need to recompile vast swathes of your codebase anytime an upstream header file is modified.

Reply on news.ycombinator.com