Add SFINAE for the slice operator with DiscreteDomain for a Chunk (#1012)

Author: tpadioleau

include/ddc/chunk.hpp

@@ -169,14 +169,20 @@ class Chunk : public ChunkCommon<ElementType, SupportType, Kokkos::layout_right>
     }
 
     /// Slice out some dimensions
-    template <class... QueryDDims>
+    template <
+            class... QueryDDims,
+            class SFINAESupportType = SupportType,
+            std::enable_if_t<is_discrete_domain_v<SFINAESupportType>, int> = 0>
     auto operator[](DiscreteDomain<QueryDDims...> const& odomain) const
     {
         return span_view()[odomain];
     }
 
     /// Slice out some dimensions
-    template <class... QueryDDims>
+    template <
+            class... QueryDDims,
+            class SFINAESupportType = SupportType,
+            std::enable_if_t<is_discrete_domain_v<SFINAESupportType>, int> = 0>
     auto operator[](DiscreteDomain<QueryDDims...> const& odomain)
     {
         return span_view()[odomain];

include/ddc/chunk_span.hpp

@@ -308,7 +308,7 @@ class ChunkSpan : public ChunkCommon<ElementType, SupportType, LayoutStridedPoli
     template <
             class... QueryDDims,
             class SFINAESupportType = SupportType,
-            std::enable_if_t<is_discrete_domain_v<SFINAESupportType>, std::nullptr_t> = nullptr>
+            std::enable_if_t<is_discrete_domain_v<SFINAESupportType>, int> = 0>
     KOKKOS_FUNCTION constexpr auto operator[](DiscreteDomain<QueryDDims...> const& odomain) const
     {
         KOKKOS_ASSERT(