feature/spaceship: Clause 21: Strings (#1635)

Co-authored-by: Anju Del Moral Gonzalez <[email protected]>
Co-authored-by: Casey Carter <[email protected]>
Co-authored-by: Stephan T. Lavavej <[email protected]>

Author: 4 people

stl/inc/xstring

@@ -39,6 +39,9 @@ struct _Char_traits { // properties of a string or stream element
     using pos_type   = streampos;
     using off_type   = streamoff;
     using state_type = _Mbstatet;
+#if _HAS_CXX20
+    using comparison_category = strong_ordering;
+#endif // _HAS_CXX20
 
     // For copy/move, we can uniformly call memcpy/memmove (or their builtin versions) for all element types.
 
@@ -217,6 +220,9 @@ public:
     using pos_type   = streampos;
     using off_type   = streamoff;
     using state_type = mbstate_t;
+#if _HAS_CXX20
+    using comparison_category = strong_ordering;
+#endif // _HAS_CXX20
 
     using _Primary_char_traits::_Copy_s;
     using _Primary_char_traits::copy;
@@ -355,6 +361,9 @@ public:
     using pos_type   = streampos;
     using off_type   = streamoff;
     using state_type = mbstate_t;
+#if _HAS_CXX20
+    using comparison_category = strong_ordering;
+#endif // _HAS_CXX20
 
     using _Primary_char_traits::_Copy_s;
     using _Primary_char_traits::copy;
@@ -1659,19 +1668,21 @@ _NODISCARD constexpr bool operator==(
     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
 
 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
 // FUNCTION TEMPLATES operator!= FOR basic_string_view
 template <class _Elem, class _Traits>
 _NODISCARD constexpr bool operator!=(
@@ -1770,7 +1781,37 @@ _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 = typename _Traits::comparison_category;
+
+    static_assert(_Is_any_of_v<type, partial_ordering, weak_ordering, strong_ordering>,
+        "N4878 [string.view.comparison]/4: Mandates: R denotes a comparison category type.");
+};
+
+template <class _Traits>
+using _Get_comparison_category_t = typename _Get_comparison_category<_Traits>::type;
+
+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);
+}
 
+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
 
 // TYPEDEFS FOR basic_string_view
 using string_view = basic_string_view<char>;
@@ -4512,13 +4553,26 @@ _NODISCARD bool operator==(
 }
 
 template <class _Elem, class _Traits, class _Alloc>
-_NODISCARD bool operator==(_In_z_ const _Elem* const _Left, const basic_string<_Elem, _Traits, _Alloc>& _Right) {
-    return _Right._Equal(_Left);
+_NODISCARD bool operator==(const basic_string<_Elem, _Traits, _Alloc>& _Left, _In_z_ const _Elem* const _Right) {
+    return _Left._Equal(_Right);
 }
 
+#if _HAS_CXX20
 template <class _Elem, class _Traits, class _Alloc>
-_NODISCARD bool operator==(const basic_string<_Elem, _Traits, _Alloc>& _Left, _In_z_ const _Elem* const _Right) {
-    return _Left._Equal(_Right);
+_NODISCARD _Get_comparison_category_t<_Traits> operator<=>(
+    const basic_string<_Elem, _Traits, _Alloc>& _Left, const basic_string<_Elem, _Traits, _Alloc>& _Right) noexcept {
+    return static_cast<_Get_comparison_category_t<_Traits>>(_Left.compare(_Right) <=> 0);
+}
+
+template <class _Elem, class _Traits, class _Alloc>
+_NODISCARD _Get_comparison_category_t<_Traits> operator<=>(
+    const basic_string<_Elem, _Traits, _Alloc>& _Left, _In_z_ const _Elem* const _Right) {
+    return static_cast<_Get_comparison_category_t<_Traits>>(_Left.compare(_Right) <=> 0);
+}
+#else // ^^^ _HAS_CXX20 / !_HAS_CXX20 vvv
+template <class _Elem, class _Traits, class _Alloc>
+_NODISCARD bool operator==(_In_z_ const _Elem* const _Left, const basic_string<_Elem, _Traits, _Alloc>& _Right) {
+    return _Right._Equal(_Left);
 }
 
 template <class _Elem, class _Traits, class _Alloc>
@@ -4600,6 +4654,7 @@ template <class _Elem, class _Traits, class _Alloc>
 _NODISCARD bool operator>=(const basic_string<_Elem, _Traits, _Alloc>& _Left, _In_z_ const _Elem* const _Right) {
     return !(_Left < _Right);
 }
+#endif // ^^^ !_HAS_CXX20 ^^^
 
 using string  = basic_string<char, char_traits<char>, allocator<char>>;
 using wstring = basic_string<wchar_t, char_traits<wchar_t>, allocator<wchar_t>>;

tests/std/tests/P1614R2_spaceship/test.cpp

@@ -1,9 +1,6 @@
 // Copyright (c) Microsoft Corporation.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-// Covers:
-// * spaceship for containers
-
 #include <array>
 #include <cassert>
 #include <compare>
@@ -21,6 +18,7 @@
 #include <set>
 #include <stack>
 #include <string>
+#include <string_view>
 #include <system_error>
 #include <thread>
 #include <type_traits>
@@ -434,27 +432,148 @@ void ordering_test_cases() {
         std::ssub_match sm3       = m3[0];
         std::ssub_match sm4       = m4[0];
 
-        // TRANSITION, std::char_traits<char> doesn't define comparison_category
-        spaceship_test<std::weak_ordering>(sm1, sm1_equal, sm2);
-        spaceship_test<std::weak_ordering>(sm1, s1, s2);
-        spaceship_test<std::weak_ordering>(sm1, s1.c_str(), s2.c_str());
-        spaceship_test<std::weak_ordering>(sm3, 'c', 'm');
-        spaceship_test<std::weak_ordering>(s1, sm1, sm2);
-        spaceship_test<std::weak_ordering>(s1.c_str(), sm1, sm2);
-        spaceship_test<std::weak_ordering>('c', sm3, sm4);
+        spaceship_test<std::strong_ordering>(sm1, sm1_equal, sm2);
+        spaceship_test<std::strong_ordering>(sm1, s1, s2);
+        spaceship_test<std::strong_ordering>(sm1, s1.c_str(), s2.c_str());
+        spaceship_test<std::strong_ordering>(sm3, 'c', 'm');
+        spaceship_test<std::strong_ordering>(s1, sm1, sm2);
+        spaceship_test<std::strong_ordering>(s1.c_str(), sm1, sm2);
+        spaceship_test<std::strong_ordering>('c', sm3, sm4);
 
         using StronglyOrderedMatch = std::ssub_match;
         using WeaklyOrderedMatch   = std::sub_match<std::basic_string<WeaklyOrderedChar>::const_iterator>;
         using WeaklyOrderdByOmissionMatch =
             std::sub_match<std::basic_string<WeaklyOrderedByOmissionChar>::const_iterator>;
         using PartiallyOrderedMatch = std::sub_match<std::basic_string<PartiallyOrderedChar>::const_iterator>;
 
-        // TRANSITION, std::char_traits<char> doesn't define comparison_category
-        static_assert(std::is_same_v<SpaceshipType<StronglyOrderedMatch>, std::weak_ordering>);
+        static_assert(std::is_same_v<SpaceshipType<StronglyOrderedMatch>, std::strong_ordering>);
         static_assert(std::is_same_v<SpaceshipType<WeaklyOrderedMatch>, std::weak_ordering>);
         static_assert(std::is_same_v<SpaceshipType<WeaklyOrderdByOmissionMatch>, std::weak_ordering>);
         static_assert(std::is_same_v<SpaceshipType<PartiallyOrderedMatch>, std::partial_ordering>);
     }
+    { // char_traits
+        static_assert(std::is_same_v<std::char_traits<char>::comparison_category, std::strong_ordering>);
+#ifdef __cpp_char8_t
+        static_assert(std::is_same_v<std::char_traits<char8_t>::comparison_category, std::strong_ordering>);
+#endif // __cpp_char8_t
+        static_assert(std::is_same_v<std::char_traits<char16_t>::comparison_category, std::strong_ordering>);
+        static_assert(std::is_same_v<std::char_traits<char32_t>::comparison_category, std::strong_ordering>);
+        static_assert(std::is_same_v<std::char_traits<wchar_t>::comparison_category, std::strong_ordering>);
+    }
+    { // Strings library
+        const std::string a1 = "abcdef";
+        const std::string a2 = "abcdef";
+        const std::string a3 = "abcdefg";
+        const std::string a4 = "abcde";
+        const std::string a5 = "abddef";
+        const std::string a6 = "abbdef";
+
+        assert((a1 <=> a2) == std::strong_ordering::equivalent);
+        assert((a1 <=> a3) == std::strong_ordering::less);
+        assert((a1 <=> a4) == std::strong_ordering::greater);
+        assert((a1 <=> a5) == std::strong_ordering::less);
+        assert((a1 <=> a6) == std::strong_ordering::greater);
+
+        assert(a1 == a2);
+        assert(a1 >= a2);
+        assert(a1 <= a2);
+        assert(a1 < a3);
+        assert(a1 <= a3);
+        assert(a1 != a3);
+        assert(a1 > a4);
+        assert(a1 >= a4);
+        assert(a1 != a4);
+        assert(a1 < a5);
+        assert(a1 <= a5);
+        assert(a1 != a5);
+        assert(a1 > a6);
+        assert(a1 >= a6);
+        assert(a1 != a6);
+
+        assert((a1 <=> "aardvark") == std::strong_ordering::greater);
+        assert((a1 <=> "abcdef") == std::strong_ordering::equivalent);
+        assert((a1 <=> "zebra") == std::strong_ordering::less);
+
+        assert(("aardvark" <=> a1) == std::strong_ordering::less);
+        assert(("abcdef" <=> a1) == std::strong_ordering::equivalent);
+        assert(("zebra" <=> a1) == std::strong_ordering::greater);
+    }
+    { // string_view
+        const std::string_view a1 = "abcdef";
+        const std::string_view a2 = "abcdef";
+        const std::string_view a3 = "abcdefg";
+        const std::string_view a4 = "abcde";
+        const std::string_view a5 = "abddef";
+        const std::string_view a6 = "abbdef";
+
+        assert((a1 <=> a2) == std::strong_ordering::equivalent);
+        assert((a1 <=> a3) == std::strong_ordering::less);
+        assert((a1 <=> a4) == std::strong_ordering::greater);
+        assert((a1 <=> a5) == std::strong_ordering::less);
+        assert((a1 <=> a6) == std::strong_ordering::greater);
+
+        assert(a1 == a2);
+        assert(a1 >= a2);
+        assert(a1 <= a2);
+        assert(a1 < a3);
+        assert(a1 <= a3);
+        assert(a1 != a3);
+        assert(a1 > a4);
+        assert(a1 >= a4);
+        assert(a1 != a4);
+        assert(a1 < a5);
+        assert(a1 <= a5);
+        assert(a1 != a5);
+        assert(a1 > a6);
+        assert(a1 >= a6);
+        assert(a1 != a6);
+
+        assert((a1 <=> "aardvark") == std::strong_ordering::greater);
+        assert((a1 <=> "abcdef") == std::strong_ordering::equivalent);
+        assert((a1 <=> "zebra") == std::strong_ordering::less);
+
+        assert(("aardvark" <=> a1) == std::strong_ordering::less);
+        assert(("abcdef" <=> a1) == std::strong_ordering::equivalent);
+        assert(("zebra" <=> a1) == std::strong_ordering::greater);
+    }
+    { // constexpr string_view
+        constexpr std::string_view a1 = "abcdef";
+        constexpr std::string_view a2 = "abcdef";
+        constexpr std::string_view a3 = "abcdefg";
+        constexpr std::string_view a4 = "abcde";
+        constexpr std::string_view a5 = "abddef";
+        constexpr std::string_view a6 = "abbdef";
+
+        static_assert((a1 <=> a2) == std::strong_ordering::equivalent);
+        static_assert((a1 <=> a3) == std::strong_ordering::less);
+        static_assert((a1 <=> a4) == std::strong_ordering::greater);
+        static_assert((a1 <=> a5) == std::strong_ordering::less);
+        static_assert((a1 <=> a6) == std::strong_ordering::greater);
+
+        static_assert(a1 == a2);
+        static_assert(a1 >= a2);
+        static_assert(a1 <= a2);
+        static_assert(a1 < a3);
+        static_assert(a1 <= a3);
+        static_assert(a1 != a3);
+        static_assert(a1 > a4);
+        static_assert(a1 >= a4);
+        static_assert(a1 != a4);
+        static_assert(a1 < a5);
+        static_assert(a1 <= a5);
+        static_assert(a1 != a5);
+        static_assert(a1 > a6);
+        static_assert(a1 >= a6);
+        static_assert(a1 != a6);
+
+        static_assert((a1 <=> "aardvark") == std::strong_ordering::greater);
+        static_assert((a1 <=> "abcdef") == std::strong_ordering::equivalent);
+        static_assert((a1 <=> "zebra") == std::strong_ordering::less);
+
+        static_assert(("aardvark" <=> a1) == std::strong_ordering::less);
+        static_assert(("abcdef" <=> a1) == std::strong_ordering::equivalent);
+        static_assert(("zebra" <=> a1) == std::strong_ordering::greater);
+    }
     { // Diagnostics Library
         diagnostics_test<std::error_code>();
         diagnostics_test<std::error_condition>();