[libcxx-commits] [libcxx] [libc++] Implement P2897R7 aligned_accessor: An mdspan accessor expressing pointer over-alignment (PR #122603)

[Louis Dionne 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
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
+
+// <mdspan>
+
+//  template<class ElementType, size_t ByteAlignment>
+//  struct aligned_accessor {
+//    using offset_policy = default_accessor<ElementType>;
+//    using element_type = ElementType;
+//    using reference = ElementType&;
+//    using data_handle_type = ElementType*;
+//
+//    static constexpr size_t byte_alignment = ByteAlignment;
+//
+//    ...
+//  };
+//
+//  Each specialization of aligned_accessor is a trivially copyable type that models semiregular.
+
+#include <mdspan>
+#include <type_traits>
+#include <concepts>
+#include <cassert>
+
+#include "test_macros.h"
+
+#include "../MinimalElementType.h"
+
+template <class T, size_t N>
+void test_types() {
+  using A = std::aligned_accessor<T, N>;
+  ASSERT_SAME_TYPE(typename A::offset_policy, std::default_accessor<T>);
+  ASSERT_SAME_TYPE(typename A::element_type, T);
+  ASSERT_SAME_TYPE(typename A::reference, T&);
+  ASSERT_SAME_TYPE(typename A::data_handle_type, T*);
+
+  ASSERT_SAME_TYPE(decltype(A::byte_alignment), const size_t);
----------------
ldionne wrote:

```suggestion
  ASSERT_SAME_TYPE(decltype(A::byte_alignment), const std::size_t);
```

https://github.com/llvm/llvm-project/pull/122603