[libc++][NFC] Simplify the implementation of string and string_views operator==

Author: philnik777

libcxx/include/string

@@ -1881,11 +1881,6 @@ public:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __clear_and_shrink() _NOEXCEPT;
 
 private:
-  template <class _Alloc>
-  inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool friend
-  operator==(const basic_string<char, char_traits<char>, _Alloc>& __lhs,
-             const basic_string<char, char_traits<char>, _Alloc>& __rhs) _NOEXCEPT;
-
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __shrink_or_extend(size_type __target_capacity);
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_STRING_INTERNAL_MEMORY_ACCESS bool
@@ -3842,37 +3837,10 @@ template <class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool
 operator==(const basic_string<_CharT, _Traits, _Allocator>& __lhs,
            const basic_string<_CharT, _Traits, _Allocator>& __rhs) _NOEXCEPT {
-#  if _LIBCPP_STD_VER >= 20
-  return basic_string_view<_CharT, _Traits>(__lhs) == basic_string_view<_CharT, _Traits>(__rhs);
-#  else
   size_t __lhs_sz = __lhs.size();
   return __lhs_sz == __rhs.size() && _Traits::compare(__lhs.data(), __rhs.data(), __lhs_sz) == 0;
-#  endif
 }
 
-template <class _Allocator>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool
-operator==(const basic_string<char, char_traits<char>, _Allocator>& __lhs,
-           const basic_string<char, char_traits<char>, _Allocator>& __rhs) _NOEXCEPT {
-  size_t __sz = __lhs.size();
-  if (__sz != __rhs.size())
-    return false;
-  return char_traits<char>::compare(__lhs.data(), __rhs.data(), __sz) == 0;
-}
-
-#  if _LIBCPP_STD_VER <= 17
-template <class _CharT, class _Traits, class _Allocator>
-inline _LIBCPP_HIDE_FROM_ABI bool
-operator==(const _CharT* __lhs, const basic_string<_CharT, _Traits, _Allocator>& __rhs) _NOEXCEPT {
-  typedef basic_string<_CharT, _Traits, _Allocator> _String;
-  _LIBCPP_ASSERT_NON_NULL(__lhs != nullptr, "operator==(char*, basic_string): received nullptr");
-  size_t __lhs_len = _Traits::length(__lhs);
-  if (__lhs_len != __rhs.size())
-    return false;
-  return __rhs.compare(0, _String::npos, __lhs, __lhs_len) == 0;
-}
-#  endif // _LIBCPP_STD_VER <= 17
-
 template <class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI bool
 operator==(const basic_string<_CharT, _Traits, _Allocator>& __lhs, const _CharT* __rhs) _NOEXCEPT {
@@ -3890,7 +3858,15 @@ operator==(const basic_string<_CharT, _Traits, _Allocator>& __lhs, const _CharT*
   return __lhs.compare(0, _String::npos, __rhs, __rhs_len) == 0;
 }
 
-#  if _LIBCPP_STD_VER >= 20
+#if _LIBCPP_STD_VER <= 17
+template <class _CharT, class _Traits, class _Allocator>
+inline _LIBCPP_HIDE_FROM_ABI bool
+operator==(const _CharT* __lhs, const basic_string<_CharT, _Traits, _Allocator>& __rhs) _NOEXCEPT {
+  return __rhs == __lhs;
+}
+#endif // _LIBCPP_STD_VER <= 17
+
+#if _LIBCPP_STD_VER >= 20
 
 template <class _CharT, class _Traits, class _Allocator>
 _LIBCPP_HIDE_FROM_ABI constexpr auto operator<=>(const basic_string<_CharT, _Traits, _Allocator>& __lhs,

libcxx/include/string_view

@@ -722,16 +722,19 @@ basic_string_view(_Range) -> basic_string_view<ranges::range_value_t<_Range>>;
 
 // [string.view.comparison]
 
-#  if _LIBCPP_STD_VER >= 20
-
-template <class _CharT, class _Traits>
-_LIBCPP_HIDE_FROM_ABI constexpr bool operator==(basic_string_view<_CharT, _Traits> __lhs,
-                                                type_identity_t<basic_string_view<_CharT, _Traits>> __rhs) noexcept {
+// The dummy default template parameters are used to work around a MSVC issue with mangling, see VSO-409326 for details.
+// This applies to the other sufficient overloads below for the other comparison operators.
+template <class _CharT, class _Traits, int = 1>
+_LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI bool
+operator==(basic_string_view<_CharT, _Traits> __lhs,
+           __type_identity_t<basic_string_view<_CharT, _Traits> > __rhs) _NOEXCEPT {
   if (__lhs.size() != __rhs.size())
     return false;
   return __lhs.compare(__rhs) == 0;
 }
 
+#if _LIBCPP_STD_VER >= 20
+
 template <class _CharT, class _Traits>
 _LIBCPP_HIDE_FROM_ABI constexpr auto operator<=>(basic_string_view<_CharT, _Traits> __lhs,
                                                  type_identity_t<basic_string_view<_CharT, _Traits>> __rhs) noexcept {
@@ -757,51 +760,32 @@ operator==(basic_string_view<_CharT, _Traits> __lhs, basic_string_view<_CharT, _
   return __lhs.compare(__rhs) == 0;
 }
 
-// The dummy default template parameters are used to work around a MSVC issue with mangling, see VSO-409326 for details.
-// This applies to the other sufficient overloads below for the other comparison operators.
-template <class _CharT, class _Traits, int = 1>
-_LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI bool
-operator==(basic_string_view<_CharT, _Traits> __lhs,
-           __type_identity_t<basic_string_view<_CharT, _Traits> > __rhs) _NOEXCEPT {
-  if (__lhs.size() != __rhs.size())
-    return false;
-  return __lhs.compare(__rhs) == 0;
-}
-
 template <class _CharT, class _Traits, int = 2>
 _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI bool
 operator==(__type_identity_t<basic_string_view<_CharT, _Traits> > __lhs,
            basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT {
-  if (__lhs.size() != __rhs.size())
-    return false;
-  return __lhs.compare(__rhs) == 0;
+  return __lhs == __rhs;
 }
 
 // operator !=
 template <class _CharT, class _Traits>
 _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI bool
 operator!=(basic_string_view<_CharT, _Traits> __lhs, basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT {
-  if (__lhs.size() != __rhs.size())
-    return true;
-  return __lhs.compare(__rhs) != 0;
+  return !(__lhs == __rhs);
 }
 
 template <class _CharT, class _Traits, int = 1>
 _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI bool
 operator!=(basic_string_view<_CharT, _Traits> __lhs,
            __type_identity_t<basic_string_view<_CharT, _Traits> > __rhs) _NOEXCEPT {
-  if (__lhs.size() != __rhs.size())
-    return true;
-  return __lhs.compare(__rhs) != 0;
+  return !(__lhs == __rhs);
 }
 
 template <class _CharT, class _Traits, int = 2>
 _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI bool
 operator!=(__type_identity_t<basic_string_view<_CharT, _Traits> > __lhs,
            basic_string_view<_CharT, _Traits> __rhs) _NOEXCEPT {
-  if (__lhs.size() != __rhs.size())
-    return true;
-  return __lhs.compare(__rhs) != 0;
+  return !(__lhs == __rhs);
 }
 
 // operator <