This is a partial implementation of P2781R8. It adds std::cw and
std::constant_wrapper, but doesn't modify __integral_constant_like for
span/mdspan.
libstdc++-v3/ChangeLog:
* include/bits/version.def (constant_wrapper): Add.
* include/bits/version.h: Regenerate.
* include/std/type_traits (_CwFixedValue): New class.
(_IndexSequence): New struct.
(_BuildIndexSequence): New struct.
(_ConstExprParam): New concept.
(_CwOperators): New struct.
(constant_wrapper): New struct.
(cw): New global constant.
* testsuite/20_util/constant_wrapper/adl.cc: New test.
* testsuite/20_util/constant_wrapper/ex.cc: New test.
* testsuite/20_util/constant_wrapper/generic.cc: New test.
* testsuite/20_util/constant_wrapper/version.cc: New test.
Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
---
This is a preview to discuss certain points:
1. Is there a better way of initializing one C array with
another?
2. If no, should we refactor <utility>? If we include <utility> from
<type_traits> we're creating a circular dependency (<utility> includes
<type_traits>). One solution is to lift the required code into
a <bits/integer_sequence.h> and then include that file from both
<utility> and <type_traits>.
3. Is the type of test that will "check" each operator meaningful?
libstdc++-v3/include/bits/version.def | 8 +
libstdc++-v3/include/bits/version.h | 10 +
libstdc++-v3/include/std/type_traits | 354 ++++++++++++++++++
.../testsuite/20_util/constant_wrapper/adl.cc | 42 +++
.../testsuite/20_util/constant_wrapper/ex.cc | 45 +++
.../20_util/constant_wrapper/generic.cc | 78 ++++
.../20_util/constant_wrapper/version.cc | 11 +
7 files changed, 548 insertions(+)
create mode 100644 libstdc++-v3/testsuite/20_util/constant_wrapper/adl.cc
create mode 100644 libstdc++-v3/testsuite/20_util/constant_wrapper/ex.cc
create mode 100644 libstdc++-v3/testsuite/20_util/constant_wrapper/generic.cc
create mode 100644 libstdc++-v3/testsuite/20_util/constant_wrapper/version.cc
diff --git a/libstdc++-v3/include/bits/version.def
b/libstdc++-v3/include/bits/version.def
index dbe2cb8f175..c8253e52168 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -393,6 +393,14 @@ ftms = {
};
};
+ftms = {
+ name = constant_wrapper;
+ values = {
+ v = 202506;
+ cxxmin = 26;
+ };
+};
+
ftms = {
name = has_unique_object_representations;
values = {
diff --git a/libstdc++-v3/include/bits/version.h
b/libstdc++-v3/include/bits/version.h
index 7bb6016df68..c0512fe6579 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -430,6 +430,16 @@
#endif /* !defined(__cpp_lib_byte) && defined(__glibcxx_want_byte) */
#undef __glibcxx_want_byte
+#if !defined(__cpp_lib_constant_wrapper)
+# if (__cplusplus > 202302L)
+# define __glibcxx_constant_wrapper 202506L
+# if defined(__glibcxx_want_all) || defined(__glibcxx_want_constant_wrapper)
+# define __cpp_lib_constant_wrapper 202506L
+# endif
+# endif
+#endif /* !defined(__cpp_lib_constant_wrapper) &&
defined(__glibcxx_want_constant_wrapper) */
+#undef __glibcxx_want_constant_wrapper
+
#if !defined(__cpp_lib_has_unique_object_representations)
# if (__cplusplus >= 201703L) &&
(defined(_GLIBCXX_HAVE_BUILTIN_HAS_UNIQ_OBJ_REP))
# define __glibcxx_has_unique_object_representations 201606L
diff --git a/libstdc++-v3/include/std/type_traits
b/libstdc++-v3/include/std/type_traits
index ff23544fbf0..0c87b5bf444 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -41,6 +41,7 @@
#define __glibcxx_want_bool_constant
#define __glibcxx_want_bounded_array_traits
+#define __glibcxx_want_constant_wrapper
#define __glibcxx_want_has_unique_object_representations
#define __glibcxx_want_integral_constant_callable
#define __glibcxx_want_is_aggregate
@@ -4280,6 +4281,359 @@ template<typename _Ret, typename _Fn, typename... _Args>
#endif // C++2a
+#ifdef __cpp_lib_constant_wrapper // C++ >= 26
+ template<typename _Tp>
+ struct _CwFixedValue
+ {
+ using _S_type = _Tp;
+
+ constexpr
+ _CwFixedValue(_S_type __v) noexcept
+ : _M_data(__v) { }
+
+ _S_type _M_data;
+ };
+
+ template<size_t... _Indices>
+ struct _IndexSequence
+ { };
+
+ template<size_t _Nm, size_t... _Indices>
+ struct _BuildIndexSequence
+ {
+ using _S_type = _BuildIndexSequence<_Nm, _Indices...,
sizeof...(_Indices)>::_S_type;
+ };
+
+ template<size_t _Nm, size_t... _Indices>
+ requires (sizeof...(_Indices) == _Nm)
+ struct _BuildIndexSequence<_Nm, _Indices...>
+ {
+ using _S_type = _IndexSequence<_Indices...>;
+ };
+
+ template<typename _Tp, size_t _Extent>
+ struct _CwFixedValue<_Tp[_Extent]> {
+ using _S_type = _Tp[_Extent];
+
+ constexpr
+ _CwFixedValue(_Tp (&__arr)[_Extent]) noexcept
+ : _CwFixedValue(__arr, typename
_BuildIndexSequence<_Extent>::_S_type())
+ { }
+
+ template<size_t... _Indices>
+ constexpr
+ _CwFixedValue(_Tp (&__arr)[_Extent], _IndexSequence<_Indices...>)
noexcept
+ : _M_data{__arr[_Indices]...}
+ { }
+
+ _Tp _M_data[_Extent];
+ };
+
+ template<typename _Tp, size_t _Extent>
+ _CwFixedValue(_Tp (&)[_Extent]) -> _CwFixedValue<_Tp[_Extent]>;
+
+ template<_CwFixedValue _Tp,
+ typename = typename decltype(_CwFixedValue(_Tp))::_S_type>
+ struct constant_wrapper;
+
+
+ template<typename _Tp>
+ concept _ConstExprParam = requires
+ {
+ typename constant_wrapper<_Tp::value>;
+ };
+
+ struct _CwOperators
+ {
+ template<_ConstExprParam _Tp>
+ friend constexpr auto
+ operator+(_Tp) noexcept -> constant_wrapper<(+_Tp::value)>
+ { return {}; }
+ template<_ConstExprParam _Tp>
+ friend constexpr auto
+ operator-(_Tp) noexcept -> constant_wrapper<(-_Tp::value)>
+ { return {}; }
+ template<_ConstExprParam _Tp>
+ friend constexpr auto
+ operator~(_Tp) noexcept -> constant_wrapper<(~_Tp::value)>
+ { return {}; }
+ template<_ConstExprParam _Tp>
+ friend constexpr auto
+ operator!(_Tp) noexcept -> constant_wrapper<(!_Tp::value)>
+ { return {}; }
+ template<_ConstExprParam _Tp>
+ friend constexpr auto
+ operator&(_Tp) noexcept -> constant_wrapper<(&_Tp::value)>
+ { return {}; }
+ template<_ConstExprParam _Tp>
+ friend constexpr auto
+ operator*(_Tp) noexcept -> constant_wrapper<(*_Tp::value)>
+ { return {}; }
+
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator+(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value + _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator-(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value - _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator*(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value * _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator/(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value / _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator%(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value % _Right::value)>
+ { return {}; }
+
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator<<(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value << _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator>>(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value >> _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator&(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value & _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator|(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value | _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator^(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value ^ _Right::value)>
+ { return {}; }
+
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ requires (!is_constructible_v<bool, decltype(_Left::value)>
+ || !is_constructible_v<bool, decltype(_Right::value)>)
+ friend constexpr auto
+ operator&&(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value && _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ requires (!is_constructible_v<bool, decltype(_Left::value)>
+ || !is_constructible_v<bool, decltype(_Right::value)>)
+ friend constexpr auto
+ operator||(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value || _Right::value)>
+ { return {}; }
+
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator<=>(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value <=> _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator<(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value < _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator<=(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value <= _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator==(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value == _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator!=(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value != _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator>(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value > _Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator>=(_Left, _Right) noexcept
+ -> constant_wrapper<(_Left::value >= _Right::value)>
+ { return {}; }
+
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator,(_Left, _Right) noexcept = delete;
+ template<_ConstExprParam _Left, _ConstExprParam _Right>
+ friend constexpr auto
+ operator->*(_Left, _Right) noexcept
+ -> constant_wrapper<_Left::value->*(_Right::value)>
+ { return {}; }
+ template<_ConstExprParam _Tp, _ConstExprParam... _Args>
+ constexpr auto
+ operator()(this _Tp, _Args...) noexcept
+ requires
+ requires(_Args...) { constant_wrapper<_Tp::value(_Args::value...)>(); }
+ { return constant_wrapper<_Tp::value(_Args::value...)>{}; }
+ template<_ConstExprParam _Tp, _ConstExprParam... _Args>
+ constexpr auto
+ operator[](this _Tp, _Args...) noexcept
+ -> constant_wrapper<(_Tp::value[_Args::value...])>
+ { return {}; }
+
+ // pseudo-mutators
+ template<_ConstExprParam _Tp>
+ constexpr auto
+ operator++(this _Tp) noexcept
+ requires requires(_Tp::value_type __x) { ++__x; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return ++__x; }()>{};
+ }
+ template<_ConstExprParam _Tp>
+ constexpr auto
+ operator++(this _Tp, int) noexcept
+ requires requires(_Tp::value_type __x) { __x++; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x++; }()>{};
+ }
+
+ template<_ConstExprParam _Tp>
+ constexpr auto
+ operator--(this _Tp) noexcept
+ requires requires(_Tp::value_type __x) { --__x; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return --__x; }()>{};
+ }
+ template<_ConstExprParam _Tp>
+ constexpr auto
+ operator--(this _Tp, int) noexcept
+ requires requires(_Tp::value_type __x) { __x--; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x--; }()>{};
+ }
+
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator+=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x += _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x += _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator-=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x -= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x -= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator*=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x *= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x *= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator/=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x /= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x /= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator%=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x %= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x %= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator&=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x &= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x &= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator|=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x |= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x |= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator^=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x ^= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x ^= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator<<=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x <<= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x <<= _Right::value; }()>{};
+ }
+ template<_ConstExprParam _Tp, _ConstExprParam _Right>
+ constexpr auto
+ operator>>=(this _Tp, _Right) noexcept
+ requires requires(_Tp::value_type __x) { __x >>= _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = _Tp::value; return __x >>= _Right::value; }()>{};
+ }
+ };
+
+ template<_CwFixedValue _X, typename>
+ struct constant_wrapper : _CwOperators {
+ static constexpr const auto& value = _X._M_data;
+ using type = constant_wrapper;
+ using value_type = typename decltype(_X)::_S_type;
+
+ template<_ConstExprParam _Right>
+ constexpr auto
+ operator=(_Right) const noexcept
+ requires requires(value_type __x) { __x = _Right::value; }
+ {
+ return constant_wrapper<
+ [] { auto __x = value; return __x = _Right::value; }()>{};
+ }
+
+ constexpr
+ operator decltype(auto)() const noexcept
+ { return value; }
+ };
+
+ template<_CwFixedValue _Tp>
+ constexpr auto cw = constant_wrapper<_Tp>{};
+#endif
+
/// @} group metaprogramming
_GLIBCXX_END_NAMESPACE_VERSION
diff --git a/libstdc++-v3/testsuite/20_util/constant_wrapper/adl.cc
b/libstdc++-v3/testsuite/20_util/constant_wrapper/adl.cc
new file mode 100644
index 00000000000..7ee754fe4b1
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/constant_wrapper/adl.cc
@@ -0,0 +1,42 @@
+// { dg-do run { target c++26 } }
+#include <type_traits>
+
+#include <testsuite_hooks.h>
+
+namespace adl
+{
+ struct Addable
+ {
+ double x;
+
+ friend constexpr Addable
+ operator+(Addable lhs, Addable rhs)
+ { return Addable{lhs.x + rhs.x}; }
+
+ friend constexpr bool
+ operator==(Addable lhs, Addable rhs)
+ { return lhs.x == rhs.x; }
+ };
+}
+
+constexpr void
+test_addable()
+{
+ auto check = [](auto a, auto b)
+ {
+ if constexpr (a + b == adl::Addable{5.0})
+ return true;
+ else
+ return false;
+ };
+
+ constexpr adl::Addable a{2.0}, b{3.0};
+ VERIFY(check(std::cw<a>, std::cw<b>));
+}
+
+int
+main()
+{
+ test_addable();
+ return 0;
+}
diff --git a/libstdc++-v3/testsuite/20_util/constant_wrapper/ex.cc
b/libstdc++-v3/testsuite/20_util/constant_wrapper/ex.cc
new file mode 100644
index 00000000000..f46af929030
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/constant_wrapper/ex.cc
@@ -0,0 +1,45 @@
+// { dg-do run { target c++26 } }
+#include <type_traits>
+
+#include <testsuite_hooks.h>
+
+constexpr auto
+initial_phase(auto quantity_1, auto quantity_2)
+{ return quantity_1 + quantity_2; }
+
+constexpr auto
+middle_phase(auto tbd)
+{ return tbd; }
+
+constexpr bool
+final_phase(auto gathered, auto available)
+{
+ if constexpr (gathered == available)
+ return true;
+ else
+ return false;
+}
+
+void
+impeccable_underground_planning()
+{
+ auto gathered_quantity = middle_phase(initial_phase(std::cw<42>,
std::cw<13>));
+ static_assert(gathered_quantity == 55);
+ auto all_available = std::cw<55>;
+ VERIFY(final_phase(gathered_quantity, all_available));
+}
+
+// void
+// deeply_flawed_underground_planning()
+// {
+// constexpr auto gathered_quantity = middle_phase(initial_phase(42, 13));
+// constexpr auto all_available = 55;
+// final_phase(gathered_quantity, all_available);
+// }
+
+int
+main()
+{
+ impeccable_underground_planning();
+ return 0;
+}
diff --git a/libstdc++-v3/testsuite/20_util/constant_wrapper/generic.cc
b/libstdc++-v3/testsuite/20_util/constant_wrapper/generic.cc
new file mode 100644
index 00000000000..4381ac43639
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/constant_wrapper/generic.cc
@@ -0,0 +1,78 @@
+// { dg-do run { target c++26 } }
+#include <type_traits>
+#include <utility>
+
+#include <testsuite_hooks.h>
+
+constexpr void
+test_c_arrays()
+{
+ constexpr double x[] = {1.1, 2.2, 3.3};
+ auto access = [](auto x, size_t i)
+ {
+ return x[i];
+ };
+
+ VERIFY(access(std::cw<x>, 0) == x[0]);
+ VERIFY(access(std::cw<x>, 1) == x[1]);
+ VERIFY(access(std::cw<x>, 2) == x[2]);
+}
+
+constexpr void
+test_ints()
+{
+ std::constant_wrapper<2> two;
+ VERIFY(two + 3 == 5);
+}
+
+template<int OpId>
+ struct Int
+ {
+ friend constexpr int
+ operator+(Int) noexcept requires(OpId == 0)
+ { return OpId; }
+
+ friend constexpr int
+ operator-(Int) noexcept requires(OpId == 1)
+ { return OpId; }
+
+ int value;
+ };
+
+template<int OpId>
+ constexpr void
+ test_unary_operator()
+ {
+ auto x = std::cw<Int<OpId>{-1}>;
+ if constexpr (OpId == 0)
+ VERIFY((+x).value == OpId);
+ if constexpr (OpId == 1)
+ VERIFY((-x).value == OpId);
+ }
+
+constexpr void
+test_unary_operator_all()
+{
+ auto run_all = []<size_t... Idx>(std::integer_sequence<size_t, Idx...>)
+ {
+ (test_unary_operator<Idx>(), ...);
+ };
+ run_all(std::make_index_sequence<2>());
+}
+
+constexpr bool
+test_all()
+{
+ test_c_arrays();
+ test_ints();
+ test_unary_operator_all();
+ return true;
+}
+
+int
+main()
+{
+ test_all();
+ static_assert(test_all());
+ return 0;
+}
diff --git a/libstdc++-v3/testsuite/20_util/constant_wrapper/version.cc
b/libstdc++-v3/testsuite/20_util/constant_wrapper/version.cc
new file mode 100644
index 00000000000..4fee6159141
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/constant_wrapper/version.cc
@@ -0,0 +1,11 @@
+// { dg-do preprocess { target c++26 } }
+// { dg-add-options no_pch }
+
+#include <type_traits>
+
+#ifndef __cpp_lib_constant_wrapper
+#error "Feature test macro __cpp_lib_constant_wrapper is missing for
<type_traits>"
+#if __cpp_lib_constant_wrapper < 202506L
+#error "Feature test macro __cpp_lib_constant_wrapper has the wrong value"
+#endif
+#endif
--
2.50.0
