[libcxx-commits] [libcxx] [libc++][optional] LWG4497: `std::nullopt_t` should be comparable (PR #214975)

[Hristo Hristov via libcxx-commits]

================
@@ -0,0 +1,102 @@
+//===----------------------------------------------------------------------===//
+//
+// 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"
+
+#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() {
+  { // ==
+    auto result = (std::nullopt == std::nullopt);
+    static_assert(std::is_same_v<decltype(result), bool>);
+    static_assert(noexcept(std::nullopt == std::nullopt));
+
+    assert(result);
+  }
+  { // !=
+    auto result = (std::nullopt != std::nullopt);
+    static_assert(std::is_same_v<decltype(result), bool>);
+    static_assert(noexcept(std::nullopt != std::nullopt));
+
+    assert(!result);
+  }
+  { // <=
+    auto result = (std::nullopt <= std::nullopt);
+    static_assert(std::is_same_v<decltype(result), bool>);
+    static_assert(noexcept(std::nullopt <= std::nullopt));
+
+    assert(result);
+  }
+  { // >=
+    auto result = (std::nullopt >= std::nullopt);
+    static_assert(std::is_same_v<decltype(result), bool>);
+    static_assert(noexcept(std::nullopt >= std::nullopt));
+
+    assert(result);
+  }
+  { // >
+    auto result = (std::nullopt > std::nullopt);
+    static_assert(std::is_same_v<decltype(result), bool>);
+    static_assert(noexcept(std::nullopt > std::nullopt));
+
+    assert(!(std::nullopt > std::nullopt));
+  }
+  { // <
+    auto result = (std::nullopt < std::nullopt);
+    static_assert(std::is_same_v<decltype(result), bool>);
+    static_assert(noexcept(std::nullopt < std::nullopt));
+
+    assert(!result);
+  }
+
+#if TEST_STD_VER >= 20
+  { // <=>
+    std::same_as<std::strong_ordering> auto result = (std::nullopt <=> std::nullopt);
+    static_assert(noexcept(std::nullopt <=> std::nullopt));
+
+    assert(result == std::strong_ordering::equal);
+  }
+
+  { // Test ranges::find with nullopt
+    std::vector<std::optional<int>> v = {1, 2, std::nullopt, 4, 5};
+
+    auto it = std::ranges::find(v, std::nullopt);
+
+    assert(it != v.end());
+    assert(*it == std::nullopt);
+  }
+#endif
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+  static_assert(test());
----------------
Zingam wrote:

@frederick-vs-ja From https://cplusplus.github.io/LWG/issue4612

" it was found that almost no intended operation is specified to be have desired property"

I think there is a typo _"to be have desired property_" that doesn't seem to make sense.

https://github.com/llvm/llvm-project/pull/214975