Am Di., 14. März 2023 um 12:02 Uhr schrieb Jonathan Wakely <jwak...@redhat.com>: > > On Tue, 14 Mar 2023 at 10:51, Daniel Krügler wrote: >> >> Apologies for the late response: >> > > I only just committed the change, so it's not delayed :-) > > >> >> What about changing the test to check for __cpp_inline_variables or >> combining it with __cpp_variable_templates instead? >> > > We could do that, but it would complicate their use. > > Currently they're only used in C++17 code (chrono::floor etc.) and C++20 code > (chrono::hh_mm_ss etc. and chrono formatters). We know it's OK for C++17 and > C++20 code to use __is_duration_v and __is_time_point_v because they're > defined for C++17 and later. > > If we change them to be defined for __cpp_inline_variables && > __cpp_variable_templates then what changes? It should be safe to assume we > can still use them in C++17 and C++20 code, but could we also use them > elsewhere, e.g. in C++14 code such as chrono::literals? Maybe, but only if > __cpp_inline_variables is defined for C++14 mode, and if it's not, then we'd > need something like: > > #if __cplusplus >= 201402L > template<typename _Dur> > #if __cpp_inline_variables > enable_if_t<__is_duration_v<_Dur>, _Dur> > #else > enable_if_t<__is_duration<_Dur>::value, _Dur> > #endif > foo(const _Dur&); > #endif > > And this is not an improvement over simply: > > #if __cplusplus >= 201402L > template<typename _Dur> > enable_if_t<__is_duration<_Dur>::value, _Dur> > foo(const _Dur&); > #endif > > So I don't see why we would want to do it. I think it was a mistake for me to > ever make them depend on __cpp_variable_templates, instead of just depending > on C++17. I think it's better to fix that mistake.
Sounds reasonable, thanks. - Daniel
