Another C++26 paper just approved in Wrocław. The std::monostate class
is defined in <variant> since C++17, but for C++26 it should also be
available in <utility>.
libstdc++-v3/ChangeLog:
* include/Makefile.am: Add bits/monostate.h.
* include/Makefile.in: Regenerate.
* include/std/utility: Include <bits/monostate.h>.
* include/std/variant (monostate, hash<monostate>): Move
definitions to ...
* include/bits/monostate.h: New file.
* testsuite/20_util/headers/utility/synopsis.cc: Add monostate
and hash<monostate> declarations.
* testsuite/20_util/monostate/requirements.cc: New test.
---
Tested x86_64-linux.
libstdc++-v3/include/Makefile.am | 1 +
libstdc++-v3/include/Makefile.in | 1 +
libstdc++-v3/include/bits/monostate.h | 78 +++++++++++++++++++
libstdc++-v3/include/std/utility | 4 +
libstdc++-v3/include/std/variant | 31 +-------
.../20_util/headers/utility/synopsis.cc | 5 ++
.../20_util/monostate/requirements.cc | 38 +++++++++
7 files changed, 128 insertions(+), 30 deletions(-)
create mode 100644 libstdc++-v3/include/bits/monostate.h
create mode 100644 libstdc++-v3/testsuite/20_util/monostate/requirements.cc
diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
index 422a0f4bd0a..6efd3cd5f1c 100644
--- a/libstdc++-v3/include/Makefile.am
+++ b/libstdc++-v3/include/Makefile.am
@@ -133,6 +133,7 @@ bits_freestanding = \
${bits_srcdir}/iterator_concepts.h \
${bits_srcdir}/max_size_type.h \
${bits_srcdir}/memoryfwd.h \
+ ${bits_srcdir}/monostate.h \
${bits_srcdir}/move.h \
${bits_srcdir}/out_ptr.h \
${bits_srcdir}/predefined_ops.h \
diff --git a/libstdc++-v3/include/Makefile.in b/libstdc++-v3/include/Makefile.in
index 9fd4ab4848c..3b5f93ce185 100644
--- a/libstdc++-v3/include/Makefile.in
+++ b/libstdc++-v3/include/Makefile.in
@@ -488,6 +488,7 @@ bits_freestanding = \
${bits_srcdir}/iterator_concepts.h \
${bits_srcdir}/max_size_type.h \
${bits_srcdir}/memoryfwd.h \
+ ${bits_srcdir}/monostate.h \
${bits_srcdir}/move.h \
${bits_srcdir}/out_ptr.h \
${bits_srcdir}/predefined_ops.h \
diff --git a/libstdc++-v3/include/bits/monostate.h
b/libstdc++-v3/include/bits/monostate.h
new file mode 100644
index 00000000000..b6da720669a
--- /dev/null
+++ b/libstdc++-v3/include/bits/monostate.h
@@ -0,0 +1,78 @@
+// Definition of std::monostate for <variant> and <utility> -*- C++ -*-
+
+// Copyright (C) 2016-2024 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file bits/monostate.h
+ * This is an internal header file, included by other library headers.
+ * Do not attempt to use it directly. @headername{utility}
+ */
+
+#ifndef _GLIBCXX_MONOSTATE_H
+#define _GLIBCXX_MONOSTATE_H 1
+
+#include <bits/version.h>
+
+#ifdef __glibcxx_variant // C++ >= 17
+
+#include <bits/functional_hash.h>
+#if __cplusplus >= 202002L
+# include <compare>
+#endif
+
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+ struct monostate { };
+
+ constexpr bool operator==(monostate, monostate) noexcept { return true; }
+#ifdef __cpp_lib_three_way_comparison
+ constexpr strong_ordering
+ operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
+#else
+ constexpr bool operator!=(monostate, monostate) noexcept { return false; }
+ constexpr bool operator<(monostate, monostate) noexcept { return false; }
+ constexpr bool operator>(monostate, monostate) noexcept { return false; }
+ constexpr bool operator<=(monostate, monostate) noexcept { return true; }
+ constexpr bool operator>=(monostate, monostate) noexcept { return true; }
+#endif
+
+ template<>
+ struct hash<monostate>
+ {
+#if __cplusplus < 202002L
+ using result_type [[__deprecated__]] = size_t;
+ using argument_type [[__deprecated__]] = monostate;
+#endif
+
+ size_t
+ operator()(const monostate&) const noexcept
+ {
+ constexpr size_t __magic_monostate_hash = -7777;
+ return __magic_monostate_hash;
+ }
+ };
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace std
+#endif // __glibcxx_variant
+#endif /* _GLIBCXX_MONOSTATE_H */
diff --git a/libstdc++-v3/include/std/utility b/libstdc++-v3/include/std/utility
index 877e9a85c71..6b2943c821b 100644
--- a/libstdc++-v3/include/std/utility
+++ b/libstdc++-v3/include/std/utility
@@ -81,6 +81,10 @@
#include <ext/numeric_traits.h> // __is_standard_integer, __int_traits
#endif
+#if __cplusplus > 202302L
+# include <bits/monostate.h>
+#endif
+
#define __glibcxx_want_addressof_constexpr
#define __glibcxx_want_as_const
#define __glibcxx_want_constexpr_algorithms
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 32e53998083..f46b553d78e 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -45,6 +45,7 @@
#include <bits/exception_defines.h>
#include <bits/functional_hash.h>
#include <bits/invoke.h>
+#include <bits/monostate.h>
#include <bits/parse_numbers.h> // _Select_int
#include <bits/stl_iterator_base_funcs.h>
#include <bits/stl_construct.h>
@@ -65,7 +66,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename... _Types> class tuple;
template<typename... _Types> class variant;
- template <typename> struct hash;
template<typename _Variant>
struct variant_size;
@@ -1232,8 +1232,6 @@ namespace __variant
return std::get_if<__n>(__ptr);
}
- struct monostate { };
-
namespace __detail::__variant
{
template<typename _Ret, typename _Vp, typename _Op>
@@ -1354,8 +1352,6 @@ namespace __detail::__variant
});
}
- constexpr bool operator==(monostate, monostate) noexcept { return true; }
-
#ifdef __cpp_lib_three_way_comparison
template<typename... _Types>
requires (three_way_comparable<_Types> && ...)
@@ -1371,15 +1367,6 @@ namespace __detail::__variant
return __l <=> __r;
});
}
-
- constexpr strong_ordering
- operator<=>(monostate, monostate) noexcept { return strong_ordering::equal; }
-#else
- constexpr bool operator!=(monostate, monostate) noexcept { return false; }
- constexpr bool operator<(monostate, monostate) noexcept { return false; }
- constexpr bool operator>(monostate, monostate) noexcept { return false; }
- constexpr bool operator<=(monostate, monostate) noexcept { return true; }
- constexpr bool operator>=(monostate, monostate) noexcept { return true; }
#endif
template<typename _Visitor, typename... _Variants>
@@ -2030,22 +2017,6 @@ namespace __detail::__variant
#endif
{ };
- template<>
- struct hash<monostate>
- {
-#if __cplusplus < 202002L
- using result_type [[__deprecated__]] = size_t;
- using argument_type [[__deprecated__]] = monostate;
-#endif
-
- size_t
- operator()(const monostate&) const noexcept
- {
- constexpr size_t __magic_monostate_hash = -7777;
- return __magic_monostate_hash;
- }
- };
-
template<typename... _Types>
struct __is_fast_hash<hash<variant<_Types...>>>
: bool_constant<(__is_fast_hash<_Types>::value && ...)>
diff --git a/libstdc++-v3/testsuite/20_util/headers/utility/synopsis.cc
b/libstdc++-v3/testsuite/20_util/headers/utility/synopsis.cc
index 51e88b70f51..73c3b51fa44 100644
--- a/libstdc++-v3/testsuite/20_util/headers/utility/synopsis.cc
+++ b/libstdc++-v3/testsuite/20_util/headers/utility/synopsis.cc
@@ -137,6 +137,11 @@ namespace std {
struct in_place_t;
template<class> struct in_place_type_t;
template<size_t> struct in_place_index_t;
+
+#if __cplusplus > 202302L
+ struct monostate;
+ template<> struct hash<monostate>;
+#endif
#endif
#endif
}
diff --git a/libstdc++-v3/testsuite/20_util/monostate/requirements.cc
b/libstdc++-v3/testsuite/20_util/monostate/requirements.cc
new file mode 100644
index 00000000000..c385862c885
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/monostate/requirements.cc
@@ -0,0 +1,38 @@
+// { dg-do compile { target c++17 } }
+
+#if __cplusplus <= 202302L
+# include <variant>
+#else
+# include <utility>
+#endif
+
+void
+test01()
+{
+ static_assert( std::is_nothrow_default_constructible_v<std::monostate> );
+ static_assert( std::is_nothrow_copy_constructible_v<std::monostate> );
+ static_assert( std::is_nothrow_copy_assignable_v<std::monostate> );
+ static_assert( std::is_nothrow_destructible_v<std::monostate> );
+}
+
+void
+test02()
+{
+#ifdef __cpp_lib_three_way_comparison
+ static_assert( std::is_eq(std::monostate{} <=> std::monostate{}) );
+#endif
+ static_assert( std::monostate{} == std::monostate{} );
+ static_assert( std::monostate{} <= std::monostate{} );
+ static_assert( std::monostate{} >= std::monostate{} );
+ static_assert( !(std::monostate{} != std::monostate{}) );
+ static_assert( !(std::monostate{} < std::monostate{}) );
+ static_assert( !(std::monostate{} > std::monostate{}) );
+}
+
+void
+test03()
+{
+ std::monostate m;
+ std::hash<std::monostate> h;
+ static_assert( std::is_same_v<decltype(h(m)), std::size_t> );
+}
--
2.47.0
