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.
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.
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.
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.
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?
I have heard rumors that certain people in the Visual Studio team have exaggerated the state of their modules implementation to speedrun the standardization process. I have no idea if that is really true, but it would explain a lot of things...
I'm not the only one who is asking these questions:
> I don’t know if they exaggerated their claims at the time, or if they didn’t properly fund the Visual Studio team since or what, but you can’t tell me 8 years wasn’t enough to make syntax highlighting work with modules. And if it is, then maybe there was something deeply wrong in their proposal and the committee should have asked to see the receipts before voting yes.
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