Add variant-based loadChunk

Author: franzpoeschel

include/openPMD/LoadStoreChunk.hpp

@@ -121,6 +121,10 @@ class ConfigureLoadStore : protected internal::ConfigureLoadStoreData
 
     template <typename T>
     [[nodiscard]] auto enqueueLoad() -> std::shared_ptr<T>;
+
+    using shared_ptr_dataset_types = auxiliary::detail::
+        map_variant<auxiliary::detail::as_shared_pointer, dataset_types>::type;
+    [[nodiscard]] auto enqueueLoadVariant() -> shared_ptr_dataset_types;
 };
 
 template <typename Ptr_Type, typename ChildClass = void>

src/LoadStoreChunk.cpp

@@ -133,6 +133,29 @@ auto ConfigureLoadStore<ChildClass>::enqueueLoad() -> std::shared_ptr<T>
     return m_rc.loadChunkAllocate_impl<T>(storeChunkConfig());
 }
 
+namespace
+{
+    template <typename ConfigureLoadStore_t>
+    struct VisitorEnqueueLoadVariant
+    {
+        template <typename T>
+        static auto call(RecordComponent const &, ConfigureLoadStore_t &cfg) ->
+            typename ConfigureLoadStore_t::shared_ptr_dataset_types
+        {
+            return cfg.template enqueueLoad<T>();
+        }
+    };
+} // namespace
+
+template <typename ChildClass>
+auto ConfigureLoadStore<ChildClass>::enqueueLoadVariant()
+    -> shared_ptr_dataset_types
+{
+    return m_rc
+        .visit<VisitorEnqueueLoadVariant<ConfigureLoadStore<ChildClass>>>(
+            *this);
+}
+
 template <typename Ptr_Type, typename ChildClass>
 ConfigureStoreChunkFromBuffer<Ptr_Type, ChildClass>::
     ConfigureStoreChunkFromBuffer(Ptr_Type buffer, parent_t &&parent)

test/SerialIOTest.cpp

@@ -1676,13 +1676,17 @@ inline void write_test(const std::string &backend)
     auto opaqueTypeDataset = rc.visit<ReadFromAnyType>();
 
     auto variantTypeDataset = rc.loadChunkVariant();
+    auto variantTypeDataset2 = rc.prepareLoadStore().enqueueLoadVariant();
     rc.seriesFlush();
-    std::visit(
-        [](auto &&shared_ptr) {
-            std::cout << "First value in loaded chunk: '" << shared_ptr.get()[0]
-                      << '\'' << std::endl;
-        },
-        variantTypeDataset);
+    for (auto ptr : {&variantTypeDataset, &variantTypeDataset2})
+    {
+        std::visit(
+            [](auto &&shared_ptr) {
+                std::cout << "First value in loaded chunk: '"
+                          << shared_ptr.get()[0] << '\'' << std::endl;
+            },
+            *ptr);
+    }
 
 #ifndef _WIN32
     REQUIRE(read.rankTable(/* collective = */ false) == compare);