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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r14-6993] libstdc++: Implement P2918R0 "Runtime format strings II" for C++26 Date: Mon, 8 Jan 2024 01:15:37 +0000 (GMT) [thread overview] Message-ID: <20240108011537.D47CA3860743@sourceware.org> (raw) https://gcc.gnu.org/g:cddaff46adfd831d4836f29dc5e21f73eaed37b3 commit r14-6993-gcddaff46adfd831d4836f29dc5e21f73eaed37b3 Author: Jonathan Wakely <jwakely@redhat.com> Date: Sun Jan 7 23:14:31 2024 +0000 libstdc++: Implement P2918R0 "Runtime format strings II" for C++26 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. Diff: --- libstdc++-v3/include/std/format | 22 +++++++++++++ .../testsuite/std/format/runtime_format.cc | 37 ++++++++++++++++++++++ 2 files changed, 59 insertions(+) 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) + { } + [[__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 + // [format.formatter], formatter /// The primary template of std::formatter is disabled. diff --git a/libstdc++-v3/testsuite/std/format/runtime_format.cc b/libstdc++-v3/testsuite/std/format/runtime_format.cc new file mode 100644 index 00000000000..174334c7676 --- /dev/null +++ b/libstdc++-v3/testsuite/std/format/runtime_format.cc @@ -0,0 +1,37 @@ +// { dg-do run { target c++26 } } + +#include <format> +#include <testsuite_hooks.h> + +void +test_char() +{ + std::string fmt = "{}"; + auto s = std::format(std::runtime_format(fmt), 123); + VERIFY( s == "123" ); +} + +void +test_wchar() +{ + std::wstring fmt = L"{:#o}"; + auto s = std::format(std::runtime_format(fmt), 456); + VERIFY( s == L"0710" ); +} + +void +test_internal_api() +{ + // Using _Runtime_format_string directly works even in C++20 mode. + // This can be used internally by libstdc++. + std::string fmt = "{:#x}"; + auto s = std::format(std::__format::_Runtime_format_string<char>(fmt), 789); + VERIFY( s == "0x315" ); +} + +int main() +{ + test_char(); + test_wchar(); + test_internal_api(); +}
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