From edae61736ca990794bc392ebed25ce4052d4d682 Mon Sep 17 00:00:00 2001
From: Mark Hoemmen <mhoemmen@nvidia.com>
Date: Mon, 8 Apr 2024 10:05:42 -0600
Subject: [PATCH] Implement P2389R1 (add dims template alias)

---
 include/experimental/__p2389_bits/dims.hpp | 28 ++++++++
 include/mdspan/mdspan.hpp                  |  1 +
 tests/CMakeLists.txt                       |  1 +
 tests/test_dims.cpp                        | 75 ++++++++++++++++++++++
 4 files changed, 105 insertions(+)
 create mode 100644 include/experimental/__p2389_bits/dims.hpp
 create mode 100644 tests/test_dims.cpp

diff --git a/include/experimental/__p2389_bits/dims.hpp b/include/experimental/__p2389_bits/dims.hpp
new file mode 100644
index 00000000..00045215
--- /dev/null
+++ b/include/experimental/__p2389_bits/dims.hpp
@@ -0,0 +1,28 @@
+//@HEADER
+// ************************************************************************
+//
+//                        Kokkos v. 4.0
+//       Copyright (2022) National Technology & Engineering
+//               Solutions of Sandia, LLC (NTESS).
+//
+// Under the terms of Contract DE-NA0003525 with NTESS,
+// the U.S. Government retains certain rights in this software.
+//
+// Part of Kokkos, under the Apache License v2.0 with LLVM Exceptions.
+// See https://kokkos.org/LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//@HEADER
+
+#pragma once
+
+// backward compatibility import into experimental
+namespace MDSPAN_IMPL_STANDARD_NAMESPACE {
+namespace MDSPAN_IMPL_PROPOSED_NAMESPACE {
+
+template< ::std::size_t Rank, class IndexType = std::size_t>
+using dims =
+  :: MDSPAN_IMPL_STANDARD_NAMESPACE :: dextents<IndexType, Rank>;
+
+} // namespace MDSPAN_IMPL_PROPOSED_NAMESPACE
+} // namespace MDSPAN_IMPL_STANDARD_NAMESPACE
diff --git a/include/mdspan/mdspan.hpp b/include/mdspan/mdspan.hpp
index ac72a1a4..4a0e354f 100644
--- a/include/mdspan/mdspan.hpp
+++ b/include/mdspan/mdspan.hpp
@@ -38,5 +38,6 @@
 #include "../experimental/__p2642_bits/layout_padded.hpp"
 #include "../experimental/__p2630_bits/submdspan.hpp"
 #endif
+#include "../experimental/__p2389_bits/dims.hpp"
 
 #endif // MDSPAN_HPP_
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index f8420b42..1dcebcbd 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -48,6 +48,7 @@ else()
   )
 endif()
 
+mdspan_add_test(test_dims)
 mdspan_add_test(test_extents)
 mdspan_add_test(test_mdspan_ctors)
 mdspan_add_test(test_mdspan_swap)
diff --git a/tests/test_dims.cpp b/tests/test_dims.cpp
new file mode 100644
index 00000000..4de05e7f
--- /dev/null
+++ b/tests/test_dims.cpp
@@ -0,0 +1,75 @@
+//@HEADER
+// ************************************************************************
+//
+//                        Kokkos v. 4.0
+//       Copyright (2022) National Technology & Engineering
+//               Solutions of Sandia, LLC (NTESS).
+//
+// Under the terms of Contract DE-NA0003525 with NTESS,
+// the U.S. Government retains certain rights in this software.
+//
+// Part of Kokkos, under the Apache License v2.0 with LLVM Exceptions.
+// See https://kokkos.org/LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//@HEADER
+
+#include <mdspan/mdspan.hpp>
+#include <type_traits>
+#include <gtest/gtest.h>
+
+namespace test {
+
+template<class Extents>
+static constexpr bool is_extents_v = false;
+
+template<class IndexType, std::size_t ... Exts>
+static constexpr bool is_extents_v<
+  MDSPAN_IMPL_STANDARD_NAMESPACE :: extents<IndexType, Exts...>
+> = true;
+
+template<std::size_t Rank>
+void test_dims_with_one_template_argument()
+{
+  using d = MDSPAN_IMPL_STANDARD_NAMESPACE :: MDSPAN_IMPL_PROPOSED_NAMESPACE :: dims<Rank>;
+  static_assert(test::is_extents_v<d>);
+  static_assert(std::is_same_v<typename d::index_type, std::size_t>);
+  static_assert(d::rank() == Rank);
+}
+
+template<std::size_t Rank, class ExpectedIndexType>
+void test_dims_with_two_template_arguments()
+{
+  using d = MDSPAN_IMPL_STANDARD_NAMESPACE :: MDSPAN_IMPL_PROPOSED_NAMESPACE :: dims<Rank, ExpectedIndexType>;
+  static_assert(test::is_extents_v<d>);
+  static_assert(std::is_same_v<typename d::index_type, ExpectedIndexType>);
+  static_assert(d::rank() == Rank);
+}
+  
+} // namespace test
+
+TEST(TestDims, Test0)
+{
+  using test::test_dims_with_one_template_argument;
+  using test::test_dims_with_two_template_arguments;
+
+  test_dims_with_one_template_argument<0>();
+  test_dims_with_one_template_argument<1>();
+  test_dims_with_one_template_argument<2>();
+  test_dims_with_one_template_argument<3>();
+  test_dims_with_one_template_argument<4>();
+  test_dims_with_one_template_argument<5>();
+  test_dims_with_one_template_argument<6>();
+  test_dims_with_one_template_argument<7>();
+  test_dims_with_one_template_argument<8>();
+
+  test_dims_with_two_template_arguments<0, std::size_t>();
+  test_dims_with_two_template_arguments<1, std::size_t>();
+  test_dims_with_two_template_arguments<2, std::size_t>();
+  test_dims_with_two_template_arguments<3, std::size_t>();
+  test_dims_with_two_template_arguments<4, std::size_t>();
+  test_dims_with_two_template_arguments<5, std::size_t>();
+  test_dims_with_two_template_arguments<6, std::size_t>();
+  test_dims_with_two_template_arguments<7, std::size_t>();
+  test_dims_with_two_template_arguments<8, std::size_t>();
+}