Re: [committed] libstdc++: Fix preprocessor condition for inline variables
Am Di., 14. März 2023 um 12:02 Uhr schrieb Jonathan Wakely : > > 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 > #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 > 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
Re: [committed] libstdc++: Fix preprocessor condition for inline variables
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 #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 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.
Re: [committed] libstdc++: Fix preprocessor condition for inline variables
Am Di., 14. März 2023 um 11:32 Uhr schrieb Jonathan Wakely via Libstdc++ : > > Tested x86_64-linux. Pushed to trunk. > > -- >8 -- > > Although variable templates are valid in C++14, inline ones aren't. > These are only used in C++17 (or later) code, so they don't need to be > defined for C++14. > > libstdc++-v3/ChangeLog: > > * include/bits/chrono.h (__is_duration_v, __is_time_point_v): > Only define for C++17 and later. > --- > libstdc++-v3/include/bits/chrono.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/libstdc++-v3/include/bits/chrono.h > b/libstdc++-v3/include/bits/chrono.h > index b2e4f4c33a8..fb99fe5eed7 100644 > --- a/libstdc++-v3/include/bits/chrono.h > +++ b/libstdc++-v3/include/bits/chrono.h > @@ -244,7 +244,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION >using __disable_if_is_duration > = typename enable_if::value, _Tp>::type; > > -#if __cpp_variable_templates > +#if __cplusplus >= 201703L > template >inline constexpr bool __is_duration_v = false; > template > -- > 2.39.2 Apologies for the late response: What about changing the test to check for __cpp_inline_variables or combining it with __cpp_variable_templates instead? Thanks, - Daniel
[committed] libstdc++: Fix preprocessor condition for inline variables
Tested x86_64-linux. Pushed to trunk. -- >8 -- Although variable templates are valid in C++14, inline ones aren't. These are only used in C++17 (or later) code, so they don't need to be defined for C++14. libstdc++-v3/ChangeLog: * include/bits/chrono.h (__is_duration_v, __is_time_point_v): Only define for C++17 and later. --- libstdc++-v3/include/bits/chrono.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libstdc++-v3/include/bits/chrono.h b/libstdc++-v3/include/bits/chrono.h index b2e4f4c33a8..fb99fe5eed7 100644 --- a/libstdc++-v3/include/bits/chrono.h +++ b/libstdc++-v3/include/bits/chrono.h @@ -244,7 +244,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION using __disable_if_is_duration = typename enable_if::value, _Tp>::type; -#if __cpp_variable_templates +#if __cplusplus >= 201703L template inline constexpr bool __is_duration_v = false; template -- 2.39.2
