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feature/spaceship: Clause 20: variant, monostate #1657

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merged 6 commits into from
Feb 19, 2021
Merged

feature/spaceship: Clause 20: variant, monostate #1657

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53d8eec
Spaceship operator for variant
d-winsor Feb 17, 2021
0bf12f3
formating
d-winsor Feb 17, 2021
13c01a1
Feedback and EDG test failures
d-winsor Feb 18, 2021
ab06d68
Added requires clause
d-winsor Feb 18, 2021
c507423
Merge branch 'feature/spaceship' into spaceship-variant
StephanTLavavej Feb 18, 2021
68a8cff
Code review feedback.
StephanTLavavej Feb 18, 2021
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46 changes: 36 additions & 10 deletions stl/inc/variant
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Original file line number Diff line number Diff line change
Expand Up @@ -1365,13 +1365,14 @@ _NODISCARD constexpr add_pointer_t<const _Ty> get_if(
}

// RELATIONAL OPERATORS [variant.relops]
template <class _Op, class... _Types>
struct _Variant_relop_visitor { // evaluate _Op with the contained value of two variants that hold the same alternative
template <class _Op, class _Result, class... _Types>
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struct _Variant_relop_visitor2 { // evaluate _Op with the contained value of two variants that hold the same alternative
const _Variant_storage<_Types...>& _Left;

template <class _Ty, size_t _Idx>
_NODISCARD constexpr bool operator()(_Tagged<const _Ty&, _Idx> _Right) const noexcept(
disjunction_v<bool_constant<_Idx == variant_npos>, is_nothrow_invocable_r<bool, _Op, const _Ty&, const _Ty&>>) {
_NODISCARD constexpr _Result operator()(_Tagged<const _Ty&, _Idx> _Right) const
noexcept(disjunction_v<bool_constant<_Idx == variant_npos>,
is_nothrow_invocable_r<_Result, _Op, const _Ty&, const _Ty&>>) {
// determine the relationship between the stored values of _Left and _Right
// pre: _Left.index() == _Idx && _Right.index() == _Idx
if constexpr (_Idx != variant_npos) {
Expand All @@ -1387,7 +1388,7 @@ template <class... _Types>
_NODISCARD constexpr bool operator==(const variant<_Types...>& _Left, const variant<_Types...>& _Right) noexcept(
conjunction_v<is_nothrow_invocable_r<bool, equal_to<>, const _Types&, const _Types&>...>) /* strengthened */ {
// determine if the arguments are both valueless or contain equal values
using _Visitor = _Variant_relop_visitor<equal_to<>, _Types...>;
using _Visitor = _Variant_relop_visitor2<equal_to<>, bool, _Types...>;
const size_t _Right_index = _Right.index();
return _Left.index() == _Right_index
&& _Variant_raw_visit(_Right_index, _Right._Storage(), _Visitor{_Left._Storage()});
Expand All @@ -1397,7 +1398,7 @@ template <class... _Types>
_NODISCARD constexpr bool operator!=(const variant<_Types...>& _Left, const variant<_Types...>& _Right) noexcept(
conjunction_v<is_nothrow_invocable_r<bool, not_equal_to<>, const _Types&, const _Types&>...>) /* strengthened */ {
// determine if the arguments have different active alternatives or contain unequal values
using _Visitor = _Variant_relop_visitor<not_equal_to<>, _Types...>;
using _Visitor = _Variant_relop_visitor2<not_equal_to<>, bool, _Types...>;
const size_t _Right_index = _Right.index();
return _Left.index() != _Right_index
|| _Variant_raw_visit(_Right_index, _Right._Storage(), _Visitor{_Left._Storage()});
Expand All @@ -1408,7 +1409,7 @@ _NODISCARD constexpr bool operator<(const variant<_Types...>& _Left, const varia
conjunction_v<is_nothrow_invocable_r<bool, less<>, const _Types&, const _Types&>...>) /* strengthened */ {
// determine if _Left has a lesser index(), or equal index() and lesser
// contained value than _Right
using _Visitor = _Variant_relop_visitor<less<>, _Types...>;
using _Visitor = _Variant_relop_visitor2<less<>, bool, _Types...>;
const size_t _Left_offset = _Left.index() + 1;
const size_t _Right_offset = _Right.index() + 1;
return _Left_offset < _Right_offset
Expand All @@ -1421,7 +1422,7 @@ _NODISCARD constexpr bool operator>(const variant<_Types...>& _Left, const varia
conjunction_v<is_nothrow_invocable_r<bool, greater<>, const _Types&, const _Types&>...>) /* strengthened */ {
// determine if _Left has a greater index(), or equal index() and
// greater contained value than _Right
using _Visitor = _Variant_relop_visitor<greater<>, _Types...>;
using _Visitor = _Variant_relop_visitor2<greater<>, bool, _Types...>;
const size_t _Left_offset = _Left.index() + 1;
const size_t _Right_offset = _Right.index() + 1;
return _Left_offset > _Right_offset
Expand All @@ -1434,7 +1435,7 @@ _NODISCARD constexpr bool operator<=(const variant<_Types...>& _Left, const vari
conjunction_v<is_nothrow_invocable_r<bool, less_equal<>, const _Types&, const _Types&>...>) /* strengthened */ {
// determine if _Left's index() is less than _Right's, or equal and
// _Left contains a value less than or equal to _Right
using _Visitor = _Variant_relop_visitor<less_equal<>, _Types...>;
using _Visitor = _Variant_relop_visitor2<less_equal<>, bool, _Types...>;
const size_t _Left_offset = _Left.index() + 1;
const size_t _Right_offset = _Right.index() + 1;
return _Left_offset < _Right_offset
Expand All @@ -1447,14 +1448,32 @@ _NODISCARD constexpr bool operator>=(const variant<_Types...>& _Left, const vari
conjunction_v<is_nothrow_invocable_r<bool, greater_equal<>, const _Types&, const _Types&>...>) /* strengthened */ {
// determine if _Left's index() is greater than _Right's, or equal and
// _Left contains a value greater than or equal to _Right
using _Visitor = _Variant_relop_visitor<greater_equal<>, _Types...>;
using _Visitor = _Variant_relop_visitor2<greater_equal<>, bool, _Types...>;
const size_t _Left_offset = _Left.index() + 1;
const size_t _Right_offset = _Right.index() + 1;
return _Left_offset > _Right_offset
|| (_Left_offset == _Right_offset
&& _Variant_raw_visit(_Right_offset - 1, _Right._Storage(), _Visitor{_Left._Storage()}));
}

#ifdef __cpp_lib_concepts
template <class... _Types>
_NODISCARD constexpr common_comparison_category_t<compare_three_way_result_t<_Types>...>
operator<=>(const variant<_Types...>& _Left, const variant<_Types...>& _Right) noexcept(
conjunction_v<is_nothrow_invocable_r<common_comparison_category_t<compare_three_way_result_t<_Types>...>,
compare_three_way, const _Types&, const _Types&>...>) /* strengthened */ {
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// Determine the three-way comparison of _Left's and _Right's index, if equal
// return the three-way comparison of the contained values of _Left and _Right
using _Visitor = _Variant_relop_visitor2<compare_three_way,
common_comparison_category_t<compare_three_way_result_t<_Types>...>, _Types...>;
const size_t _Left_offset = _Left.index() + 1;
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const size_t _Right_offset = _Right.index() + 1;
const auto _Offset_order = _Left_offset <=> _Right_offset;
return _Offset_order != 0 ? _Offset_order
: _Variant_raw_visit(_Right_offset - 1, _Right._Storage(), _Visitor{_Left._Storage()});
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}
#endif // __cpp_lib_concepts

// VISITATION [variant.visit]
template <class... _Variants>
inline constexpr size_t _Variant_total_states =
Expand Down Expand Up @@ -1698,6 +1717,12 @@ struct monostate {};
_NODISCARD constexpr bool operator==(monostate, monostate) noexcept {
return true;
}

#if _HAS_CXX20
_NODISCARD constexpr strong_ordering operator<=>(monostate, monostate) noexcept {
return strong_ordering::equal;
}
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
_NODISCARD constexpr bool operator!=(monostate, monostate) noexcept {
return false;
}
Expand All @@ -1713,6 +1738,7 @@ _NODISCARD constexpr bool operator<=(monostate, monostate) noexcept {
_NODISCARD constexpr bool operator>=(monostate, monostate) noexcept {
return true;
}
#endif // !_HAS_CXX20

// SPECIALIZED ALGORITHMS [variant.specalg]
template <class... _Types,
Expand Down
17 changes: 17 additions & 0 deletions tests/std/tests/P1614R2_spaceship/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
#include <unordered_set>
#include <utility>
#include <valarray>
#include <variant>
#include <vector>

template <class T>
Expand Down Expand Up @@ -484,6 +485,22 @@ void ordering_test_cases() {

spaceship_test<std::strong_ordering>(c_mem[0], c_mem[0], c_mem[1]);
}
{ // variant
using V = std::variant<int, long>;
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constexpr V v0_0(std::in_place_index<0>, 0);
constexpr V v0_1(std::in_place_index<0>, 1);
constexpr V v1_0(std::in_place_index<1>, 0);
constexpr V v1_1(std::in_place_index<1>, 1);

spaceship_test<std::strong_ordering>(v0_0, v0_0, v0_1);
spaceship_test<std::strong_ordering>(v0_1, v0_1, v1_0);
spaceship_test<std::strong_ordering>(v1_0, v1_0, v1_1);
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using M = std::monostate;
constexpr M m1{};
constexpr M m2{};
static_assert((m1 <=> m2) == 0);
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}
{ // slice
std::slice a1(2, 3, 4);
std::slice a2(2, 3, 4);
Expand Down