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Implement LWG-3950 std::basic_string_view comparison operators are overspecified #4510

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Mar 28, 2024
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Implement LWG-3950 std::basic_string_view comparison operators are overspecified #4510

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f922132
Implement LWG-3950
frederick-vs-ja Mar 23, 2024
a143843
`_Traits` => `Traits`
StephanTLavavej Mar 26, 2024
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66 changes: 31 additions & 35 deletions stl/inc/xstring
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Original file line number Diff line number Diff line change
Expand Up @@ -1643,27 +1643,53 @@ namespace ranges {
} // namespace ranges
#endif // _HAS_CXX20

#if _HAS_CXX20
_EXPORT_STD template <class _Elem, class _Traits>
_NODISCARD constexpr bool operator==(const basic_string_view<_Elem, _Traits> _Lhs,
const type_identity_t<basic_string_view<_Elem, _Traits>> _Rhs) noexcept {
return _Lhs._Equal(_Rhs);
}

template <class _Traits, class = void>
struct _Get_comparison_category {
using type = weak_ordering;
};

template <class _Traits>
struct _Get_comparison_category<_Traits, void_t<typename _Traits::comparison_category>> {
using type = _Traits::comparison_category;

static_assert(_Is_any_of_v<type, partial_ordering, weak_ordering, strong_ordering>,
"N4971 [string.view.comparison]/4: Mandates: R denotes a comparison category type.");
};

template <class _Traits>
using _Get_comparison_category_t = _Get_comparison_category<_Traits>::type;

_EXPORT_STD template <class _Elem, class _Traits>
_NODISCARD constexpr _Get_comparison_category_t<_Traits> operator<=>(const basic_string_view<_Elem, _Traits> _Lhs,
const type_identity_t<basic_string_view<_Elem, _Traits>> _Rhs) noexcept {
return static_cast<_Get_comparison_category_t<_Traits>>(_Lhs.compare(_Rhs) <=> 0);
}
#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
template <class _Elem, class _Traits>
_NODISCARD constexpr bool operator==(
const basic_string_view<_Elem, _Traits> _Lhs, const basic_string_view<_Elem, _Traits> _Rhs) noexcept {
return _Lhs._Equal(_Rhs);
}

#if !_HAS_CXX20
template <class _Elem, class _Traits, int = 1> // TRANSITION, VSO-409326
_NODISCARD constexpr bool operator==(
const _Identity_t<basic_string_view<_Elem, _Traits>> _Lhs, const basic_string_view<_Elem, _Traits> _Rhs) noexcept {
return _Lhs._Equal(_Rhs);
}
#endif // !_HAS_CXX20

_EXPORT_STD template <class _Elem, class _Traits, int = 2> // TRANSITION, VSO-409326
template <class _Elem, class _Traits, int = 2> // TRANSITION, VSO-409326
_NODISCARD constexpr bool operator==(
const basic_string_view<_Elem, _Traits> _Lhs, const _Identity_t<basic_string_view<_Elem, _Traits>> _Rhs) noexcept {
return _Lhs._Equal(_Rhs);
}

#if !_HAS_CXX20
template <class _Elem, class _Traits>
_NODISCARD constexpr bool operator!=(
const basic_string_view<_Elem, _Traits> _Lhs, const basic_string_view<_Elem, _Traits> _Rhs) noexcept {
Expand Down Expand Up @@ -1753,37 +1779,7 @@ _NODISCARD constexpr bool operator>=(
const basic_string_view<_Elem, _Traits> _Lhs, const _Identity_t<basic_string_view<_Elem, _Traits>> _Rhs) noexcept {
return _Lhs.compare(_Rhs) >= 0;
}
#endif // !_HAS_CXX20

#if _HAS_CXX20
template <class _Traits, class = void>
struct _Get_comparison_category {
using type = weak_ordering;
};

template <class _Traits>
struct _Get_comparison_category<_Traits, void_t<typename _Traits::comparison_category>> {
using type = _Traits::comparison_category;

static_assert(_Is_any_of_v<type, partial_ordering, weak_ordering, strong_ordering>,
"N4950 [string.view.comparison]/4: Mandates: R denotes a comparison category type.");
};

template <class _Traits>
using _Get_comparison_category_t = _Get_comparison_category<_Traits>::type;

_EXPORT_STD template <class _Elem, class _Traits>
_NODISCARD constexpr _Get_comparison_category_t<_Traits> operator<=>(
const basic_string_view<_Elem, _Traits> _Lhs, const basic_string_view<_Elem, _Traits> _Rhs) noexcept {
return static_cast<_Get_comparison_category_t<_Traits>>(_Lhs.compare(_Rhs) <=> 0);
}

_EXPORT_STD template <class _Elem, class _Traits, int = 2> // TRANSITION, VSO-409326
_NODISCARD constexpr _Get_comparison_category_t<_Traits> operator<=>(
const basic_string_view<_Elem, _Traits> _Lhs, const _Identity_t<basic_string_view<_Elem, _Traits>> _Rhs) noexcept {
return static_cast<_Get_comparison_category_t<_Traits>>(_Lhs.compare(_Rhs) <=> 0);
}
#endif // _HAS_CXX20
#endif // ^^^ !_HAS_CXX20 ^^^

_EXPORT_STD using string_view = basic_string_view<char>;
#ifdef __cpp_lib_char8_t
Expand Down
73 changes: 73 additions & 0 deletions tests/std/tests/P0220R1_string_view/test.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1261,6 +1261,79 @@ void test_C6510_warning() { // compile-only
(void) sv;
}

#if _HAS_CXX20
// LWG-3950 "std::basic_string_view comparison operators are overspecified"
namespace test_lwg_3950 {
template <class Traits>
struct get_string_comparison_category {
using type = weak_ordering;
};

template <class Traits>
requires requires { typename Traits::comparison_category; }
struct get_string_comparison_category<Traits> {
using type = Traits::comparison_category;

static_assert(disjunction_v<is_same<type, partial_ordering>, is_same<type, weak_ordering>,
is_same<type, strong_ordering>>);
};

template <class Traits>
using get_string_comparison_category_t = get_string_comparison_category<Traits>::type;

template <class Traits>
concept characterized_traits = requires { typename Traits::is_characterized; };

#ifdef __clang__ // TRANSITION, LLVM-75404
#define CONST_PARAM const
#else // ^^^ workaround / no workaround vvv
#define CONST_PARAM
#endif // ^^^ no workaround ^^^

template <class CharT, characterized_traits Traits>
constexpr bool operator==(CONST_PARAM basic_string_view<CharT, Traits> x,
CONST_PARAM type_identity_t<basic_string_view<CharT, Traits>> y) noexcept {
return x.size() == y.size() && x.compare(y) == 0;
}
template <class CharT, characterized_traits Traits>
constexpr get_string_comparison_category_t<Traits> operator<=>(CONST_PARAM basic_string_view<CharT, Traits> x,
CONST_PARAM type_identity_t<basic_string_view<CharT, Traits>> y) noexcept {
return static_cast<get_string_comparison_category_t<Traits>>(x.compare(y) <=> 0);
}

template <class CharT>
struct test_traits : char_traits<CharT> {
using is_characterized = void;
};

using test_string_view = basic_string_view<char, test_traits<char>>;

static_assert(test_string_view{} == test_string_view{});
static_assert(!(test_string_view{} != test_string_view{}));
static_assert(!(test_string_view{} < test_string_view{}));
static_assert(!(test_string_view{} > test_string_view{}));
static_assert(test_string_view{} <= test_string_view{});
static_assert(test_string_view{} >= test_string_view{});
static_assert(test_string_view{} <=> test_string_view{} == strong_ordering::equal);

static_assert(test_string_view{} == "");
static_assert(!(test_string_view{} != ""));
static_assert(!(test_string_view{} < ""));
static_assert(!(test_string_view{} > ""));
static_assert(test_string_view{} <= "");
static_assert(test_string_view{} >= "");
static_assert(test_string_view{} <=> "" == strong_ordering::equal);

static_assert("" == test_string_view{});
static_assert(!("" != test_string_view{}));
static_assert(!("" < test_string_view{}));
static_assert(!("" > test_string_view{}));
static_assert("" <= test_string_view{});
static_assert("" >= test_string_view{});
static_assert("" <=> test_string_view{} == strong_ordering::equal);
} // namespace test_lwg_3950
#endif // _HAS_CXX20

int main() {
test_case_default_constructor();
test_case_ntcts_constructor();
Expand Down
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