AaronBallman wrote: > > I can see WG21 solving this either by removing `unreachable` from `cstddef` > > or by requiring `utility` to guard against the macro via implementation > > magic (personally, I think `utility` should guard against it because of > > users including `stddef.h` directly) and it would be nice to know which > > direction the committee is leaning before we get too far into a solution. > > I'm not sure whether you mean it, but I'd expect that it's handled like > `signbit` and friends - they are functions instead of macros. For libc++ that > would simply be `#undef unreachable`, `#include <__utility/unreachable.h>` > and `using std::unreachable`.
Yeah, that would one way to handle it, but it does still defy some user expectations (and perhaps that's fine): ``` #include <stddef.h> // #include "whatever.h" // transitively includes <utility> #ifndef unreachable #error "oh no, my macro!" #endif ``` Uncommenting `whatever.h` suddenly causes an error which may be a surprise because some C standard library things remain macros even in C++ (like `offsetof`, or `va_start` and friends). Any C standard library function can be implemented as a macro, so the potential for confusion always exists, but for things defined explicitly as a macro in C, they sometimes stay a macro in C++. I think `unreachable` is probably reasonable to turn into a real function though. But another way WG21 could perhaps approach this is: ``` // In <utility> #ifndef unreachable void unreachable(); #endif ``` which retains the macro rather than the function. https://github.com/llvm/llvm-project/pull/86748 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
