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* [gcc r14-6993] libstdc++: Implement P2918R0 "Runtime format strings II" for C++26
@ 2024-01-08 1:15 Jonathan Wakely
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From: Jonathan Wakely @ 2024-01-08 1:15 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
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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