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[libc++][functional] P2944R3 (partial): Comparisons for reference_wrapper (reference_wrapper operators only) (llvm#88384)
Implements https://wg21.link/P2944R3 (partially) Implements https://wg21.link/LWG4071 / https://cplusplus.github.io/LWG/issue4071 (fixes build failures in the test suite) - https://eel.is/c++draft/refwrap.comparisons
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‎libcxx/docs/FeatureTestMacroTable.rst‎

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---------------------------------------------------------- -----------------
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``__cpp_lib_rcu`` *unimplemented*
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---------------------------------------------------------- -----------------
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``__cpp_lib_reference_wrapper`` *unimplemented*
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``__cpp_lib_reference_wrapper`` ``202403L``
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---------------------------------------------------------- -----------------
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``__cpp_lib_saturation_arithmetic`` ``202311L``
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---------------------------------------------------------- -----------------

‎libcxx/docs/ReleaseNotes/19.rst‎

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- P2869R4 - Remove Deprecated ``shared_ptr`` Atomic Access APIs from C++26
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- P2872R3 - Remove ``wstring_convert`` From C++26
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- P3142R0 - Printing Blank Lines with ``println`` (as DR against C++23)
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- P2944R3 - Comparisons for ``reference_wrapper`` (comparison operators for ``reference_wrapper`` only)
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- P2302R4 - ``std::ranges::contains``
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- P1659R3 - ``std::ranges::starts_with`` and ``std::ranges::ends_with``
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- P3029R1 - Better ``mdspan``'s CTAD

‎libcxx/docs/Status/Cxx2c.rst‎

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.. [#note-P2510R3] This paper is applied as DR against C++20. (MSVC STL and libstdc++ will do the same.)
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.. [#note-P3142R0] This paper is applied as DR against C++23. (MSVC STL and libstdc++ will do the same.)
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.. [#note-P2944R3] Implemented comparisons for ``reference_wrapper`` only.
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.. _issues-status-cxx2c:
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‎libcxx/docs/Status/Cxx2cIssues.csv‎

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"","","","","",""
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"`3343 <https://wg21.link/LWG3343>`__","Ordering of calls to ``unlock()`` and ``notify_all()`` in Effects element of ``notify_all_at_thread_exit()`` should be reversed","Not Yet Adopted","|Complete|","16.0",""
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"XXXX","","The sys_info range should be affected by save","Not Yet Adopted","|Complete|","19.0"
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"`4071 <https://wg21.link/LWG4071>`__","","``reference_wrapper`` comparisons are not SFINAE-friendly","Not Yet Adopted","|Complete|","19.0"
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"","","","","",""

‎libcxx/docs/Status/Cxx2cPapers.csv‎

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"`P2248R8 <https://wg21.link/P2248R8>`__","LWG","Enabling list-initialization for algorithms","Tokyo March 2024","","",""
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"`P2810R4 <https://wg21.link/P2810R4>`__","LWG","``is_debugger_present`` ``is_replaceable``","Tokyo March 2024","","",""
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"`P1068R11 <https://wg21.link/P1068R11>`__","LWG","Vector API for random number generation","Tokyo March 2024","","",""
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"`P2944R3 <https://wg21.link/P2944R3>`__","LWG","Comparisons for ``reference_wrapper``","Tokyo March 2024","","",""
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"`P2944R3 <https://wg21.link/P2944R3>`__","LWG","Comparisons for ``reference_wrapper``","Tokyo March 2024","|Partial| [#note-P2944R3]_","19.0",""
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"`P2642R6 <https://wg21.link/P2642R6>`__","LWG","Padded ``mdspan`` layouts","Tokyo March 2024","","",""
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"`P3029R1 <https://wg21.link/P3029R1>`__","LWG","Better ``mdspan``'s CTAD","Tokyo March 2024","|Complete|","19.0",""
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"","","","","","",""

‎libcxx/include/__functional/reference_wrapper.h‎

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#ifndef _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H
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#define _LIBCPP___FUNCTIONAL_REFERENCE_WRAPPER_H
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#include <__compare/synth_three_way.h>
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#include <__concepts/boolean_testable.h>
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#include <__config>
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#include <__functional/invoke.h>
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#include <__functional/weak_result_type.h>
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#include <__memory/addressof.h>
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#include <__type_traits/enable_if.h>
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#include <__type_traits/is_const.h>
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#include <__type_traits/remove_cvref.h>
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#include <__type_traits/void_t.h>
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#include <__utility/declval.h>
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{
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return std::__invoke(get(), std::forward<_ArgTypes>(__args)...);
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}
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#if _LIBCPP_STD_VER >= 26
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// [refwrap.comparisons], comparisons
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(reference_wrapper __x, reference_wrapper __y)
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requires requires {
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{ __x.get() == __y.get() } -> __boolean_testable;
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}
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{
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return __x.get() == __y.get();
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}
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(reference_wrapper __x, const _Tp& __y)
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requires requires {
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{ __x.get() == __y } -> __boolean_testable;
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}
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{
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return __x.get() == __y;
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}
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_LIBCPP_HIDE_FROM_ABI friend constexpr bool operator==(reference_wrapper __x, reference_wrapper<const _Tp> __y)
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requires(!is_const_v<_Tp>) && requires {
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{ __x.get() == __y.get() } -> __boolean_testable;
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}
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{
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return __x.get() == __y.get();
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}
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_LIBCPP_HIDE_FROM_ABI friend constexpr auto operator<=>(reference_wrapper __x, reference_wrapper __y)
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requires requires { std::__synth_three_way(__x.get(), __y.get()); }
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{
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return std::__synth_three_way(__x.get(), __y.get());
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}
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_LIBCPP_HIDE_FROM_ABI friend constexpr auto operator<=>(reference_wrapper __x, const _Tp& __y)
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requires requires { std::__synth_three_way(__x.get(), __y); }
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{
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return std::__synth_three_way(__x.get(), __y);
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}
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_LIBCPP_HIDE_FROM_ABI friend constexpr auto operator<=>(reference_wrapper __x, reference_wrapper<const _Tp> __y)
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requires(!is_const_v<_Tp>) && requires { std::__synth_three_way(__x.get(), __y.get()); }
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{
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return std::__synth_three_way(__x.get(), __y.get());
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}
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#endif // _LIBCPP_STD_VER >= 26
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};
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#if _LIBCPP_STD_VER >= 17

‎libcxx/include/functional‎

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template <class T> using unwrap_reference_t = typename unwrap_reference<T>::type; // since C++20
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template <class T> using unwrap_ref_decay_t = typename unwrap_ref_decay<T>::type; // since C++20
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// [refwrap.comparisons], comparisons
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friend constexpr bool operator==(reference_wrapper, reference_wrapper); // Since C++26
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friend constexpr bool operator==(reference_wrapper, const T&); // Since C++26
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friend constexpr bool operator==(reference_wrapper, reference_wrapper<const T>); // Since C++26
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friend constexpr auto operator<=>(reference_wrapper, reference_wrapper); // Since C++26
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friend constexpr auto operator<=>(reference_wrapper, const T&); // Since C++26
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friend constexpr auto operator<=>(reference_wrapper, reference_wrapper<const T>); // Since C++26
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template <class T> // <class T=void> in C++14
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struct plus {
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T operator()(const T& x, const T& y) const;

‎libcxx/include/version‎

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// # define __cpp_lib_ranges_concat 202403L
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# define __cpp_lib_ratio 202306L
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// # define __cpp_lib_rcu 202306L
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// # define __cpp_lib_reference_wrapper 202403L
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# define __cpp_lib_reference_wrapper 202403L
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# define __cpp_lib_saturation_arithmetic 202311L
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// # define __cpp_lib_smart_ptr_owner_equality 202306L
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# define __cpp_lib_span_at 202311L

‎libcxx/test/std/language.support/support.limits/support.limits.general/functional.version.compile.pass.cpp‎

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# error "__cpp_lib_ranges should have the value 202207L in c++26"
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# endif
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# if !defined(_LIBCPP_VERSION)
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# ifndef __cpp_lib_reference_wrapper
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# error "__cpp_lib_reference_wrapper should be defined in c++26"
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# endif
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# if __cpp_lib_reference_wrapper != 202403L
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# error "__cpp_lib_reference_wrapper should have the value 202403L in c++26"
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# endif
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# else // _LIBCPP_VERSION
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# ifdef __cpp_lib_reference_wrapper
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# error "__cpp_lib_reference_wrapper should not be defined because it is unimplemented in libc++!"
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# endif
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# ifndef __cpp_lib_reference_wrapper
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# error "__cpp_lib_reference_wrapper should be defined in c++26"
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# endif
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# if __cpp_lib_reference_wrapper != 202403L
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# error "__cpp_lib_reference_wrapper should have the value 202403L in c++26"
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# endif
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# ifndef __cpp_lib_result_of_sfinae

‎libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp‎

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# endif
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# endif
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# if !defined(_LIBCPP_VERSION)
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# ifndef __cpp_lib_reference_wrapper
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# error "__cpp_lib_reference_wrapper should be defined in c++26"
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# endif
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# if __cpp_lib_reference_wrapper != 202403L
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# error "__cpp_lib_reference_wrapper should have the value 202403L in c++26"
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# endif
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# else // _LIBCPP_VERSION
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# ifdef __cpp_lib_reference_wrapper
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# error "__cpp_lib_reference_wrapper should not be defined because it is unimplemented in libc++!"
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# endif
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# ifndef __cpp_lib_reference_wrapper
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# error "__cpp_lib_reference_wrapper should be defined in c++26"
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# endif
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# if __cpp_lib_reference_wrapper != 202403L
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# error "__cpp_lib_reference_wrapper should have the value 202403L in c++26"
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# endif
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# ifndef __cpp_lib_remove_cvref

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