[libcxx-commits] [libcxx] Make std::nullopt_t comparable (PR #195549)

[A. Jiang via libcxx-commits]

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@@ -362,6 +362,9 @@ struct nullopt_t {
     explicit __secret_tag() = default;
   };
   _LIBCPP_HIDE_FROM_ABI constexpr explicit nullopt_t(__secret_tag, __secret_tag) noexcept {}
+#    if _LIBCPP_STD_VER >= 26
+  _LIBCPP_HIDE_FROM_ABI constexpr strong_ordering operator<=>(const nullopt_t&) const noexcept = default;
+#    endif
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frederick-vs-ja wrote:

I think we should implement LWG4497 in C++17 and later.

For C++20 and later, we can just use `operator<=>`. In C++17 mode, there should be 6 manually written operators.

Also, IMO hidden friends are better.

https://github.com/llvm/llvm-project/pull/195549