Comments.

cpp/test/linalg/mdarray.h

@@ -142,6 +142,16 @@ class uvector_policy {
 
 namespace stdex = std::experimental;
 
+/**
+ * @brief Modified from the c++ mdarray proposal, with the differences listed below.
+ *
+ * - Layout policy is different, the mdarray in raft uses `stdex::extent` directly just
+ *   like `mdspan`, while the `mdarray` in the reference implementation uses varidic
+ *   template.
+ *
+ * - Most of the constructors from the reference implementation is removed to make sure
+ *   CUDA stream is honorred.
+ */
 template <class ElementType,
           class Extents,
           class LayoutPolicy   = stdex::layout_right,
@@ -153,11 +163,14 @@ class mdarray {
   using layout_type  = LayoutPolicy;
   using mapping_type = typename layout_type::template mapping<extents_type>;
 
-  using index_type            = size_t;
-  using difference_type       = ptrdiff_t;
+  using index_type            = std::size_t;
+  using difference_type       = std::ptrdiff_t;
   using container_policy_type = AccessorPolicy;
   using container_type        = typename container_policy_type::container_type;
 
+  static_assert(!std::is_const<ElementType>::value,
+                "Element type for container must not be const.");
+
   using pointer         = typename container_policy_type::pointer;
   using const_pointer   = typename container_policy_type::const_pointer;
   using reference       = typename container_policy_type::reference;
@@ -166,6 +179,10 @@ class mdarray {
                                   extents_type,
                                   layout_type,
                                   typename container_policy_type::accessor_policy>;
+  using const_view_type = stdex::mdspan<element_type const,
+                                        extents_type,
+                                        layout_type,
+                                        typename container_policy_type::accessor_policy>;
 
  public:
   constexpr mdarray() noexcept(std::is_nothrow_default_constructible<container_type>::value) =

cpp/test/linalg/mdspan.cu

@@ -14,19 +14,15 @@
  * limitations under the License.
  */
 #include "mdarray.h"
-#include <experimental/mdarray>
 #include <experimental/mdspan>
 #include <gtest/gtest.h>
 #include <raft/cudart_utils.h>
-#include <rmm/device_buffer.hpp>
 #include <rmm/device_uvector.hpp>
-#include <rmm/device_vector.hpp>
 #include <rmm/exec_policy.hpp>
 #include <thrust/for_each.h>
+#include <thrust/device_vector.h>
 #include <thrust/iterator/counting_iterator.h>
 
-
-
 namespace {
 namespace stdex = std::experimental;
 void test_mdspan()
@@ -35,17 +31,16 @@ void test_mdspan()
 
   cudaStream_t stream = nullptr;
   rmm::device_uvector<float> a{16ul, stream};
+  thrust::sequence(rmm::exec_policy(stream), a.begin(), a.end());
 
   stdex::mdspan<float, stdex::extents<stdex::dynamic_extent, stdex::dynamic_extent>> span{
     a.data(), 4, 4};
 
-  std::cout << "__has_cpp_attribute(no_unique_address):" << __has_cpp_attribute(no_unique_address)
-            << std::endl;
   thrust::for_each(it, it + 4, [=] __device__(size_t i) {
-    auto v = span(i, i);
-    printf("v: %f\n", v);
-    auto k = stdex::submdspan(span, stdex::full_extent, 0);
-    printf("k: %f\n", k(i));
+    auto v = span(0, i);
+    DEVICE_ASSERT(v == i);
+    auto k = stdex::submdspan(span, 0, stdex::full_extent);
+    DEVICE_ASSERT(k(i) == i);
   });
 }