[libcxx-commits] [libcxx] [libc++] LWG4497: `std::nullopt_t` should be comparable (PR #195549)

[A. Jiang via libcxx-commits]

================
@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14
+// <optional>
+
+// struct nullopt_t{see below};
+// inline constexpr nullopt_t nullopt(unspecified);
+
+// [optional.nullopt]/2:
+//  nullopt_t models copyable and three_way_comparable<strong_ordering>.
+
+#include <ratio>
+#include <vector>
+#include <ranges>
+#include <cassert>
+#include <algorithm>
+#include <optional>
+
+#include "test_macros.h"
+
+using std::nullopt;
+
----------------
frederick-vs-ja wrote:

Let's test the explicit requirements together.
```suggestion

#if TEST_STD_VER >= 20
  static_assert(std::copyable<std::nullopt_t>);
  static_assert(std::three_way_comparable<std::nullopt_t, std::strong_ordering>);
#endif

```

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