Am Mo., 8. Jan. 2024 um 03:25 Uhr schrieb Jonathan Wakely <jwak...@redhat.com>:
>
> Tested x86_64-linux and aarch64-linux. Pushed to trunk.
>
> -- >8 --
>
> This adds std::runtime_format for C++26. These new overloaded functions
> enhance the std::format API so that it isn't necessary to use the less
> ergonomic std::vformat and std::make_format_args (which are meant to be
> implementation details). This was approved in Kona 2023 for C++26.
>
> libstdc++-v3/ChangeLog:
>
> * include/std/format (__format::_Runtime_format_string): Define
> new class template.
> (basic_format_string): Add non-consteval constructor for runtime
> format strings.
> (runtime_format): Define new function for C++26.
> * testsuite/std/format/runtime_format.cc: New test.
> ---
> libstdc++-v3/include/std/format | 22 +++++++++++
> .../testsuite/std/format/runtime_format.cc | 37 +++++++++++++++++++
> 2 files changed, 59 insertions(+)
> create mode 100644 libstdc++-v3/testsuite/std/format/runtime_format.cc
>
> diff --git a/libstdc++-v3/include/std/format b/libstdc++-v3/include/std/format
> index 160efa5155c..b3b5a0bbdbc 100644
> --- a/libstdc++-v3/include/std/format
> +++ b/libstdc++-v3/include/std/format
> @@ -81,6 +81,9 @@ namespace __format
>
> template<typename _CharT>
> using __format_context = basic_format_context<_Sink_iter<_CharT>,
> _CharT>;
> +
> + template<typename _CharT>
> + struct _Runtime_format_string { basic_string_view<_CharT> _M_str; };
> } // namespace __format
> /// @endcond
>
> @@ -115,6 +118,11 @@ namespace __format
> consteval
> basic_format_string(const _Tp& __s);
>
> + [[__gnu__::__always_inline__]]
> + basic_format_string(__format::_Runtime_format_string<_CharT>&& __s)
> + : _M_str(__s._M_str)
> + { }
> +
My understanding is that this constructor should be noexcept according to N4971.
> [[__gnu__::__always_inline__]]
> constexpr basic_string_view<_CharT>
> get() const noexcept
> @@ -133,6 +141,20 @@ namespace __format
> = basic_format_string<wchar_t, type_identity_t<_Args>...>;
> #endif
>
> +#if __cplusplus > 202302L
> + [[__gnu__::__always_inline__]]
> + inline __format::_Runtime_format_string<char>
> + runtime_format(string_view __fmt)
> + { return {__fmt}; }
> +
> +#ifdef _GLIBCXX_USE_WCHAR_T
> + [[__gnu__::__always_inline__]]
> + inline __format::_Runtime_format_string<wchar_t>
> + runtime_format(wstring_view __fmt)
> + { return {__fmt}; }
> +#endif
> +#endif // C++26
> +
These runtime_format overloads should also be noexcept.
- Daniel
