Add move semantics to ViewCtorProp and ViewCtorProp<void,std::string>…

… for label

core/src/View/Kokkos_ViewCtor.hpp

@@ -113,7 +113,7 @@ struct ViewCtorProp<std::enable_if_t<is_view_label<Label>::value>, Label> {
   using type = std::string;
 
   ViewCtorProp(const type &arg) : value(arg) {}
-  ViewCtorProp(type &&arg) : value(arg) {}
+  ViewCtorProp(type &&arg) : value(std::move(arg)) {}
 
   type value;
 };
@@ -213,11 +213,16 @@ struct ViewCtorProp : public ViewCtorProp<void, P>... {
   using execution_space = typename var_execution_space::type;
   using pointer_type    = typename var_pointer::type;
 
-  /*  Copy from a matching argument list.
-   *  Requires  std::is_same< P , ViewCtorProp< void , Args >::value ...
-   */
-  template <typename... Args>
-  inline ViewCtorProp(Args const &...args) : ViewCtorProp<void, P>(args)... {}
+  // Construct from a matching argument list.
+  //
+  // Note that if P is empty, this constructor is the default constructor.
+  // On the other hand, if P is not empty, the constraint implies that
+  // there is no default constructor.
+  template <typename... Args,
+            typename = std::enable_if_t<std::conjunction_v<
+                std::is_constructible<view_ctor_prop_base<P>, Args &&>...>>>
+  ViewCtorProp(Args &&...args)
+      : ViewCtorProp<void, P>(std::forward<Args>(args))... {}
 
   template <typename... Args>
   KOKKOS_FUNCTION ViewCtorProp(pointer_type arg0, Args const &...args)
@@ -454,15 +459,14 @@ inline constexpr Kokkos::Impl::AllowPadding_t AllowPadding{};
  * alignment
  */
 template <class... Args>
-inline Impl::ViewCtorProp<typename Impl::ViewCtorProp<void, Args>::type...>
-view_alloc(Args const &...args) {
-  using return_type =
-      Impl::ViewCtorProp<typename Impl::ViewCtorProp<void, Args>::type...>;
+auto view_alloc(Args &&...args) {
+  using return_type = Impl::ViewCtorProp<typename Impl::ViewCtorProp<
+      void, Kokkos::Impl::remove_cvref_t<Args>>::type...>;
 
   static_assert(!return_type::has_pointer,
                 "Cannot give pointer-to-memory for view allocation");
 
-  return return_type(args...);
+  return return_type(std::forward<Args>(args)...);
 }
 
 template <class... Args>

core/unit_test/CMakeLists.txt

@@ -261,6 +261,7 @@ foreach(Tag Threads;Serial;OpenMP;Cuda;HPX;OpenMPTarget;OpenACC;HIP;SYCL)
         ViewCopy_b
         ViewCopy_c
         ViewCtorDimMatch
+        ViewCtorProp
         ViewEmptyRuntimeUnmanaged
         ViewHooks
         ViewLayoutStrideAssignment

core/unit_test/TestViewCtorProp.hpp

@@ -0,0 +1,95 @@
+//@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 <gtest/gtest.h>
+
+#include <Kokkos_Core.hpp>
+
+namespace {
+
+using vcp_empty_t      = Kokkos::Impl::ViewCtorProp<>;
+using vcp_label_base_t = Kokkos::Impl::ViewCtorProp<void, std::string>;
+using vcp_label_t      = Kokkos::Impl::ViewCtorProp<std::string>;
+
+// Check traits of Kokkos::Impl::ViewCtorProp<>.
+TEST(TEST_CATEGORY, vcp_empty_traits) {
+  // Check that the empty view constructor properties class is default
+  // constructible. This is needed for calls of Kokkos::view_alloc().
+  static_assert(std::is_default_constructible_v<vcp_empty_t>);
+  static_assert(std::is_same_v<decltype(Kokkos::view_alloc()), vcp_empty_t>);
+}
+
+// Check Kokkos::Impl::is_view_label.
+TEST(TEST_CATEGORY, is_view_label) {
+  static_assert(Kokkos::Impl::is_view_label<std::string>::value);
+
+  static_assert(Kokkos::Impl::is_view_label<const char[3]>::value);
+  static_assert(Kokkos::Impl::is_view_label<char[3]>::value);
+
+  // A char* is not a label. Thus, a label is distinguished from a pointer type.
+  static_assert(!Kokkos::Impl::is_view_label<char*>::value);
+}
+
+// Check traits of base class Kokkos::Impl::ViewCtorProp<void, std::string>.
+TEST(TEST_CATEGORY, vcp_label_base_traits) {
+  static_assert(std::is_same_v<typename vcp_label_base_t::type, std::string>);
+
+  // Check that the base class is default constructible. The default constructor
+  // may be called by the copy constructor of derived classes, such as when
+  // copy constructing a view constructor properties object from another view
+  // constructor properties object that holds fewer properties.
+  static_assert(std::is_default_constructible_v<vcp_label_base_t>);
+}
+
+// Check traits of derived class Kokkos::Impl::ViewCtorProp<std::string>.
+TEST(TEST_CATEGORY, vcp_label_traits) {
+  static_assert(std::is_base_of_v<vcp_label_base_t, vcp_label_t>);
+
+  static_assert(vcp_label_t::has_label);
+
+  // Check that the derived class is not default constructible. It is a design
+  // choice to not allow the default constructor to be called.
+  static_assert(!std::is_default_constructible_v<vcp_label_t>);
+}
+
+// Check that Kokkos::view_alloc perfect forwards a label passed by
+// rvalue reference, and check that the constructor
+// of Kokkos::Impl::ViewCtorProp<std::string> moves this label.
+TEST(TEST_CATEGORY, view_alloc_can_perfect_forward_label) {
+  std::string label("our label");
+
+  auto prop = Kokkos::view_alloc(std::move(label));
+
+  ASSERT_TRUE(label.empty());
+  ASSERT_EQ(Kokkos::Impl::get_property<Kokkos::Impl::LabelTag>(prop),
+            "our label");
+}
+
+// Check the copy constructor of Kokkos::Impl::ViewCtorProp<std::string>.
+TEST(TEST_CATEGORY, vcp_label_copy_constructor) {
+  // Copy construction from a view constructor properties object with a label.
+  static_assert(std::is_copy_constructible_v<vcp_label_t>);
+
+  vcp_label_t prop = Kokkos::view_alloc("our label");
+  vcp_label_t prop_copy(prop);
+
+  ASSERT_EQ(Kokkos::Impl::get_property<Kokkos::Impl::LabelTag>(prop),
+            "our label");
+  ASSERT_EQ(Kokkos::Impl::get_property<Kokkos::Impl::LabelTag>(prop_copy),
+            "our label");
+}
+
+}  // namespace