Add an assertion to the discrete_space function and a death test (#875)

* Add an assertion to the discrete_space function and a death test

* Add comment and add a check for host_discrete_space

* Apply suggestions from code review

Co-authored-by: Emily Bourne <louise.bourne@gmail.com>

---------

Co-authored-by: Emily Bourne <louise.bourne@gmail.com>

Author: tpadioleau

include/ddc/discrete_space.hpp

@@ -212,6 +212,17 @@ std::tuple<Arg0, Arg1, Args...> init_discrete_space(std::tuple<DDimImpl, Arg0, A
     return detail::extract_after(std::move(a), std::index_sequence_for<Arg0, Arg1, Args...>());
 }
 
+/**
+ * @tparam DDim a discrete dimension
+ * @return a boolean indicating whether DDim is initialized.
+ * This function indicates whether a dimension is initialized.
+ */
+template <class DDim>
+bool is_discrete_space_initialized() noexcept
+{
+    return detail::g_discrete_space_dual<DDim>.has_value();
+}
+
 /**
  * @tparam DDim a discrete dimension
  * @return the discrete space instance associated with `DDim`.
@@ -221,7 +232,9 @@ std::tuple<Arg0, Arg1, Args...> init_discrete_space(std::tuple<DDimImpl, Arg0, A
 template <class DDim, class MemorySpace = DDC_CURRENT_KOKKOS_SPACE>
 KOKKOS_FUNCTION detail::ddim_impl_t<DDim, MemorySpace> const& discrete_space()
 {
+    // This function requires that `ddc::init_discrete_space<DDim>(...);` be called first
     if constexpr (std::is_same_v<MemorySpace, Kokkos::HostSpace>) {
+        assert(is_discrete_space_initialized<DDim>());
         return detail::g_discrete_space_dual<DDim>->get_host();
     }
 #if defined(KOKKOS_ENABLE_CUDA) || defined(KOKKOS_ENABLE_HIP)
@@ -238,15 +251,11 @@ KOKKOS_FUNCTION detail::ddim_impl_t<DDim, MemorySpace> const& discrete_space()
     }
 }
 
-template <class DDim>
-bool is_discrete_space_initialized() noexcept
-{
-    return detail::g_discrete_space_dual<DDim>.has_value();
-}
-
 template <class DDim>
 detail::ddim_impl_t<DDim, Kokkos::HostSpace> const& host_discrete_space()
 {
+    // This function requires that `ddc::init_discrete_space<DDim>(...);` be called first
+    assert(is_discrete_space_initialized<DDim>());
     return detail::g_discrete_space_dual<DDim>->get_host();
 }
 

tests/discrete_space.cpp

@@ -24,3 +24,25 @@ TEST(DiscreteSpace, IsDiscreteSpaceInitialized)
             ddc::DiscreteVector<DDimX>(2)));
     EXPECT_TRUE(ddc::is_discrete_space_initialized<DDimX>());
 }
+
+TEST(DiscreteSpace, HostDiscreteSpace)
+{
+#if !defined(NDEBUG) // The assertion is only checked if NDEBUG isn't defined
+    EXPECT_DEATH(
+            ddc::host_discrete_space<DDimX>(),
+            R"rgx([Aa]ssert.*is_discrete_space_initialized<DDim>\(\))rgx");
+#else
+    GTEST_SKIP();
+#endif
+}
+
+TEST(DiscreteSpace, DiscreteSpace)
+{
+#if !defined(NDEBUG) // The assertion is only checked if NDEBUG isn't defined
+    EXPECT_DEATH(
+            ddc::discrete_space<DDimX>(),
+            R"rgx([Aa]ssert.*is_discrete_space_initialized<DDim>\(\))rgx");
+#else
+    GTEST_SKIP();
+#endif
+}