ychen added a comment. @rsmith, thanks for chiming in.
In D134772#3819502 <https://reviews.llvm.org/D134772#3819502>, @rsmith wrote: > I'm somewhat skeptical of this approach, because constrained `auto` can > appear in places within the type of an NTTP other than the top level -- for > example, in `template<C auto*>`. (Clang is non-conforming and doesn't support > this yet, but it will need to do so eventually.) Yep, I'm aware of the cases like `template<C auto*>`/`template<C auto&>`/`template<C decltype(auto)>`. It would need to retrieve the deduced type explicitly and the difference this patch brings is to look for the constraints from NTTP instead. It is not geat but doable. > In principle, there could even be multiple different constrained `auto` types > within the type of the same NTTP in the future -- I don't think that can > happen with the current language rules, but it could happen in the Concepts > TS, and it only seems to be happenstance that prevents it in C++20 rather > than design intent. Fundamentally, the constraint is not associated with the > NTTP and is instead associated with the relevant portion of the NTTP's type. I fully agree that fundamentally the constraint is associated with auto (the syntax rule suggests that too). I didn't think of the possibility that `multiple different constrained auto types within the type of the same NTTP`. It is very interesting. Any chance this approach could be tuned for that future use case? Like maintaining an array of constrains for the NTTP? > If something in the design of constrained `auto` is meaning that uniquing > isn't working properly, maybe there's some way we can address that directly? I gave a lot of thought to it but couldn't find a satisfactory approach. One way is to recreate injected template argument for constrained `auto` NTTP, but without the constraint, then use that the instantiate all the types I need for the partial ordering. It is definitely doable but pretty expensive. Any suggestions are greatly appreciated. :-) Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D134772/new/ https://reviews.llvm.org/D134772 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
