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

[A. Jiang via libcxx-commits]

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@@ -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;
+
+constexpr bool test() {
+  static_assert(nullopt == nullopt);
+  static_assert(!(nullopt != nullopt));
+  static_assert(nullopt <= nullopt);
+  static_assert(nullopt >= nullopt);
+  static_assert(!(nullopt > nullopt));
+  static_assert(!(nullopt < nullopt));
+
+#if TEST_STD_VER > 17
+  static_assert((nullopt <=> nullopt) == std::strong_ordering::equal);
+  // Test ranges::find with nullopt
+  std::vector<std::optional<int>> v = {1, 2, nullopt, 4, 5};
+  auto itr                          = std::ranges::find(v, nullopt);
+  assert(itr != v.end());
+  assert(*itr == nullopt);
+#endif
+
+  return true;
+}
+
+int main(int, char**) {
+  static_assert(test());
----------------
frederick-vs-ja wrote:

```suggestion
  test();
  static_assert(test());
```

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