[libcxx-commits] [libcxx] [libc++] Implement P1901R2: owner_hash and owner_equal for shared_ptr/weak_ptr (PR #210551)

[A. Jiang via libcxx-commits]

================
@@ -0,0 +1,70 @@
+//===----------------------------------------------------------------------===//
+//
+// 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++26
+
+// <memory>
+
+// struct owner_equal
+// {
+//     template<class T, class U>
+//         bool operator()(shared_ptr<T> const&, shared_ptr<U> const&) const noexcept;
+//     template<class T, class U>
+//         bool operator()(shared_ptr<T> const&, weak_ptr<U> const&) const noexcept;
+//     template<class T, class U>
+//         bool operator()(weak_ptr<T> const&, shared_ptr<U> const&) const noexcept;
+//     template<class T, class U>
+//         bool operator()(weak_ptr<T> const&, weak_ptr<U> const&) const noexcept;
+//
+//     using is_transparent = unspecified;
+// };
+
+#include <cassert>
+#include <concepts>
+#include <memory>
+#include <unordered_set>
+
+#include "test_macros.h"
+
+int main(int, char**) {
+  const std::shared_ptr<int> p1(new int);
+  const std::shared_ptr<int> p2 = p1;
+  const std::shared_ptr<int> p3(new int);
+  const std::weak_ptr<int> w1(p1);
+  const std::weak_ptr<int> w3(p3);
+
+  std::owner_equal oe;
+
+  std::same_as<bool> decltype(auto) result = oe(p1, p2);
+  assert(result);
+  static_assert(noexcept(oe(p1, p2)));
+  static_assert(noexcept(oe(p1, w1)));
+  static_assert(noexcept(oe(w1, p1)));
+  static_assert(noexcept(oe(w1, w1)));
+
+  assert(oe(p1, w1));
+  assert(oe(w1, p1));
+  assert(oe(w1, w1));
+
+  assert(!oe(p1, p3));
+  assert(!oe(p1, w3));
+  assert(!oe(w1, p3));
+  assert(!oe(w1, w3));
+
+  static_assert(std::same_as<std::owner_equal::is_transparent, void>);
----------------
frederick-vs-ja wrote:

We should verify that `std::owner_equal::is_transparent` is a type, but the actual type is implementation-specific (unspecified).
```suggestion
  using member_is_transparent [[maybe_unused]] = std::owner_equal::is_transparent;
  LIBCPP_STATIC_ASSERT(std::same_as<member_is_transparent, void>);
```

https://github.com/llvm/llvm-project/pull/210551