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

[Hristo Hristov via libcxx-commits]

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@@ -0,0 +1,59 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++17
+// <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 <algorithm>
+#include <cassert>
+#include <concepts>
+#include <optional>
+#include <vector>
+
+#include "test_macros.h"
+
+using std::nullopt;
+
+#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
+
+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);
----------------
Zingam wrote:

```suggestion
  auto it                          = std::ranges::find(v, nullopt);
```
Nit: FYI in libc++ context, naming iterators is either `iter` or `it`.

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