[jsd1982]

I think the conclusion section should indicate that they are based entirely on GCC 16's behavior and current implementation. We should avoid generalizing one compiler's behavior and performance. Curious how this same test would behave once clang ships C++26 reflection.

[SuperV1234]

I explicitly mentioned that GCC 16.1 was the compiler used in the benchmarking section, do you think I also need to add a disclaimer in the conclusion section as well?

Regardless, I don't think things are going to differ much with Clang. Without PCH/modules, standard header inclusion is still the "slow part" of C++ compilation, regardless of the compiler used and the standard library used (libstdc++ vs libc++). `#include` is fundamentally the same on any modern compiler.

Because the reflection feature itself seems quite fast on GCC (compared to the cost of the header), I predict the results will be similar on Clang as well.

[bluGill]

I was thinking the same thing. Modules are still not widely used, it is a reasonable guess that there are a lot of optimization opportunities left.

[SuperV1234]

That is true, but on the other hand Modules were standardized more than 6 years ago.

Promises and claims have been made for longer than that on how Modules would have improved compilation times and made everyone's lives easier. In 2026, I still have to see any real evidence of that, especially when PCH + unity builds are much easier to use (except on damn Bazel, which supports neither) and deliver great results.

If after 6+ years of development Modules are still so far behind, it is fair to question if the problem is with the design/implementability of the feature itself.

[spacechild1]

> it is fair to question if the problem is with the design/implementability of the feature itself.

The module story is just insane. How was it possible to get such a big feature into the standard without any working reference implementation? Isn't this the requirement for standard proposals to get accepted? If I compare this with how they treated JeanHeyd and his #embed proposal, the difference is staggering. To me it seems like a few powerful comittee members wanted to get modules into C++20 at any cost. This was just irresponsible.

[bluGill]

There was in visual studio which has had it other than minor details.the real problem is tools are needed to make modules work and those needed a lot of work. The work was already partially there because it's the same work that Fortran needs which tools supported but there were just enough details different to be annoying. Fortran modules were something that were always an afterthought and when tools started realizing that this is going to be a big deal, they decided they had to do it right, which took a lot of time too.

Maybe you forget Hacker News of 10 years ago, but in 2015-2016, everyone was complaining C++ doesn't have modules and how awful it must be because they're not modules. Now that C++ has modules, they're complaining about how it has modules.

[spacechild1]

I don't remember because I wasn't there :)

People are not complaining about the fact that C++ has modules, but about their usability and effectiveness. The compile time benefits seem modest and I have seen reports that it breaks Intellisense. (Maybe that's not true anymore?)

As Vittorio said, if it takes compiler vendors so long to implement them properly, maybe the design wasn't that good after all?

My point was: if you add such a big feature, shouldn't the standard require a sufficiently complete implementation? Otherwise, how can they assess whether the proposal actually works in practice and lives up to its promises?

[gpderetta]

Agree that proof of implementation and real world experience should be a requirement for standardization. But it is a catch-22: implement it's are probably not always too keen to spend time on a large feature if it is not clear that it will be standardized.

In practice both clang and VS have had some form of module support for quite a while, but the final standard ended up being different from either implementation (shaped by their experience, and certainly with inevitable last minute inventions).

I wonder if for some features the committee should vote for general guidelines, the delegate a third party (one or more implementors) to come up with both an implementation and standardese with the understanding that it will be fast-tracked in wit too much bike-shedding

[bluGill]

Again, they had a sufficiently complete implementation. That implementation was in Visual Studio, clang had a very different implementation. The standard decided to take the Microsoft version. There are pros and cons to both and I will not fault the decision but either way one of the two had to lose and there is no surprise that for something complex it will take a long time to reimplement it to whatever the new standard is.

[pjmlp]

Or VC++ if ever, which has the best modules support, but it is still trailing behind in C++23.