[libcxx-commits] [libcxx] [libc++] Implement comparison operators for `tuple` added in C++23 (PR #148799)

[Louis Dionne via libcxx-commits]

================
@@ -287,6 +294,68 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 #  ifndef _LIBCPP_CXX03_LANG
 
+template <size_t _Ip, class _Tp, class _Up>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool __tuple_compare_equal(const _Tp& __x, const _Up& __y) {
+  if constexpr (_Ip == 0)
+    return true;
+  else
+    return std::__tuple_compare_equal<_Ip - 1>(__x, __y) && std::get<_Ip - 1>(__x) == std::get<_Ip - 1>(__y);
+}
+
+#    if _LIBCPP_STD_VER >= 26
+template <class _Tp, class _Up, class _IndexSeq = make_index_sequence<tuple_size_v<_Tp>>>
+inline constexpr bool __can_tuple_compare_equal = false;
+
+// FIXME: Remove `tuple_size_v<_Tp> == tuple_size_v<_Up>` here once once LLVM-20 support ends
+// because the resolution of CWG2369 landed in LLVM-21.
+template <class _Tp, class _Up, size_t... _Is>
+  requires(tuple_size_v<_Tp> == tuple_size_v<_Up>)
+inline constexpr bool __can_tuple_compare_equal<_Tp, _Up, index_sequence<_Is...>> =
+    __all<requires(const tuple_element_t<_Is, _Tp>& __t, const tuple_element_t<_Is, _Up>& __u) {
+      { __t == __u } -> __boolean_testable;
+    }...>::value;
+#    endif // _LIBCPP_STD_VER >= 26
+
+#    if _LIBCPP_STD_VER >= 20
+template <class _Ret, class _Tp, class _Up, size_t... _Is>
+_LIBCPP_HIDE_FROM_ABI constexpr _Ret __tuple_compare_three_way(const _Tp& __x, const _Up& __y, index_sequence<_Is...>) {
+  _Ret __result = strong_ordering::equal;
+  static_cast<void>(
+      ((__result = std::__synth_three_way(std::get<_Is>(__x), std::get<_Is>(__y)), __result != 0) || ...));
+  return __result;
+}
+#    endif // _LIBCPP_STD_VER >= 20
+
+#    if _LIBCPP_STD_VER >= 23
+template <class>
+inline constexpr bool __is_tuple_v = false;
+
+template <class... _Tp>
+inline constexpr bool __is_tuple_v<tuple<_Tp...>> = true;
+
+template <class _Tp>
+concept __tuple_like_no_tuple = __tuple_like<_Tp> && !__is_tuple_v<_Tp>;
+
+template <class _Tp, class _Up, class _IndexSeq>
+struct __tuple_common_comparison_category_impl {};
+
+// FIXME: Remove `tuple_size_v<_Tp> == tuple_size_v<_Up>` here once once LLVM-20 support ends
----------------
ldionne wrote:

```suggestion
// TODO(LLVM 22): Remove `tuple_size_v<_Tp> == tuple_size_v<_Up>` here once once LLVM-20 support ends
```

https://github.com/llvm/llvm-project/pull/148799