On Mon, 26 Oct 2026 at 11:58, Tomasz Kamiński <[email protected]> wrote:
>
> Attaching below suggestions as incremental diff from yours patch.
> ---
> libstdc++-v3/include/std/chrono | 21 ++++++--
> .../time/zoned_time/custom_freestanding.cc | 48 +++++++++++++++++++
> 2 files changed, 65 insertions(+), 4 deletions(-)
> create mode 100644
> libstdc++-v3/testsuite/std/time/zoned_time/custom_freestanding.cc
>
> diff --git a/libstdc++-v3/include/std/chrono b/libstdc++-v3/include/std/chrono
> index 10e2830b66c..a74a28e73f9 100644
> --- a/libstdc++-v3/include/std/chrono
> +++ b/libstdc++-v3/include/std/chrono
> @@ -3160,6 +3160,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> };
>
> #if __cpp_lib_chrono >= 201803L // C++ >= 20 && HOSTED && USE_CXX11_ABI
> + using zoned_seconds = zoned_time<seconds>;
>
> zoned_time() -> zoned_time<seconds>;
>
> @@ -3174,6 +3175,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> const time_zone*,
> remove_cvref_t<_TimeZonePtrOrName>>;
> /// @endcond
> +#else
> + /// @cond undocumented
> + template<typename _TimeZonePtr>
> + struct __time_zone_representation_impl
> + {
> + static_assert(!std::is_convertible_v<_TimeZonePtr, string_view>,
> + "std::time_zone is not supported in freedstanding mode,"
> + " use custom time_zone representation");
> + using type = remove_cvref_t<_TimeZonePtr>;
> + };
> +
> + template<typename _TimeZonePtrOrName>
> + using __time_zone_representation
> + = typename __time_zone_representation_impl<_TimeZonePtrOrName>::type;
> + /// @endcond
> +#endif // __cpp_lib_chrono >= 201803L
>
> template<typename _TimeZonePtrOrName>
> zoned_time(_TimeZonePtrOrName&&)
> @@ -3197,10 +3214,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> -> zoned_time<common_type_t<_Duration, seconds>,
> __time_zone_representation<_TimeZonePtrOrName>>;
>
> - using zoned_seconds = zoned_time<seconds>;
> -
> -#endif // __cpp_lib_chrono >= 201803L
> -
> template<typename _Dur1, typename _TZPtr1, typename _Dur2, typename
> _TZPtr2>
> [[nodiscard]]
> inline bool
> diff --git
> a/libstdc++-v3/testsuite/std/time/zoned_time/custom_freestanding.cc
> b/libstdc++-v3/testsuite/std/time/zoned_time/custom_freestanding.cc
> new file mode 100644
> index 00000000000..ae7d1970206
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/std/time/zoned_time/custom_freestanding.cc
> @@ -0,0 +1,48 @@
> +// { dg-do run { target c++20 } }
> +
> +#include <chrono>
> +#include <type_traits>
> +#include <testsuite_hooks.h>
> +
> +struct zone_offset
> +{
> + std::chrono::seconds offset;
> +
> + template<typename Dur>
> + std::chrono::local_time<std::common_type_t<Dur, std::chrono::seconds>>
> + to_local(const std::chrono::sys_time<Dur>& tp) const noexcept
> + { return std::chrono::local_time<std::common_type_t<Dur,
> std::chrono::seconds>>(tp.time_since_epoch() + offset); }
> +
> + template<typename Dur>
> + std::chrono::sys_time<std::common_type_t<Dur, std::chrono::seconds>>
> + to_sys(const std::chrono::local_time<Dur>& tp) const noexcept
> + { return std::chrono::sys_time<std::common_type_t<Dur,
> std::chrono::seconds>>(tp.time_since_epoch() - offset); }
> +
> + // Allows zone_offset to be stored directly in zoned_time
> + const zone_offset* operator->() const noexcept
> + { return this; }
> +};
> +
> +void
> +test_custom_tzptr()
> +{
> + using namespace std::chrono;
> +
> + static_assert( !std::is_default_constructible_v<zoned_time<seconds,
> zone_offset>> );
> + static_assert( !std::is_constructible_v<zoned_time<seconds, zone_offset>,
> std::string_view> );
> +
> + zoned_time z1(zone_offset{1h}, sys_days(2012y/December/12) + 12h);
This fails the static_assert in __time_zone_representation_struct,
because zone_offset is not convertible to string_view.
> + static_assert( std::is_same_v<decltype(z1), zoned_time<seconds,
> zone_offset>> );
> + VERIFY( z1.get_sys_time() == sys_days(2012y/December/12) + 12h );
> + VERIFY( z1.get_local_time() == local_days(2012y/December/12) + 13h );
> +
> + zoned_time z2(zone_offset{1h}, local_days(2012y/December/12) + 12h);
> + static_assert( std::is_same_v<decltype(z2), zoned_time<seconds,
> zone_offset>> );
> + VERIFY( z1.get_sys_time() == sys_days(2012y/December/12) + 11h );
> + VERIFY( z1.get_local_time() == local_days(2012y/December/12) + 12h );
> +}
> +
> +int main()
> +{
> + test_custom_tzptr();
> +}
> --
> 2.56.0
>
