Avoid object slicing when using records as scalar components

include/openPMD/RecordComponent.hpp

@@ -109,6 +109,9 @@ namespace internal
     class BaseRecordData;
 } // namespace internal
 
+template <typename>
+class BaseRecord;
+
 class RecordComponent : public BaseRecordComponent
 {
     template <typename T, typename T_key, typename T_container>
@@ -134,6 +137,15 @@ class RecordComponent : public BaseRecordComponent
         AUTO
     }; // Allocation
 
+    /**
+     * @brief Avoid object slicing when using a Record as a scalar Record
+     *        Component.
+     *
+     * It's still preferred to directly use the Record, or alternatively a
+     * Record-Component-type reference to a Record.
+     */
+    RecordComponent(BaseRecord<RecordComponent> const &);
+
     RecordComponent &setUnitSI(double);
 
     /**

include/openPMD/backend/BaseRecord.hpp

@@ -212,8 +212,11 @@ class BaseRecord
     : public Container<T_elem>
     , public T_elem // T_RecordComponent
 {
+public:
     using T_RecordComponent = T_elem;
     using T_Container = Container<T_elem>;
+
+private:
     using T_Self = BaseRecord<T_elem>;
     friend class Iteration;
     friend class ParticleSpecies;

include/openPMD/backend/BaseRecordComponent.hpp

@@ -74,6 +74,9 @@ namespace internal
     };
 } // namespace internal
 
+template <typename>
+class BaseRecord;
+
 class BaseRecordComponent : virtual public Attributable
 {
     template <typename T, typename T_key, typename T_container>

include/openPMD/backend/MeshRecordComponent.hpp

@@ -52,6 +52,15 @@ class MeshRecordComponent : public RecordComponent
 public:
     ~MeshRecordComponent() override = default;
 
+    /**
+     * @brief Avoid object slicing when using a Record as a scalar Record
+     *        Component.
+     *
+     * It's still preferred to directly use the Record, or alternatively a
+     * Record-Component-type reference to a Record.
+     */
+    MeshRecordComponent(BaseRecord<MeshRecordComponent> const &);
+
     /** Position on an element
      *
      * Relative on an element (node/cell/voxel) of the mesh

include/openPMD/backend/PatchRecordComponent.hpp

@@ -84,6 +84,15 @@ class PatchRecordComponent : public BaseRecordComponent
     friend class internal::PatchRecordComponentData;
 
 public:
+    /**
+     * @brief Avoid object slicing when using a Record as a scalar Record
+     *        Component.
+     *
+     * It's still preferred to directly use the Record, or alternatively a
+     * Record-Component-type reference to a Record.
+     */
+    PatchRecordComponent(BaseRecord<PatchRecordComponent> const &);
+
     PatchRecordComponent &setUnitSI(double);
 
     virtual PatchRecordComponent &resetDataset(Dataset);

src/RecordComponent.cpp

@@ -25,6 +25,7 @@
 #include "openPMD/IO/Format.hpp"
 #include "openPMD/Series.hpp"
 #include "openPMD/auxiliary/Memory.hpp"
+#include "openPMD/backend/BaseRecord.hpp"
 
 #include <algorithm>
 #include <climits>
@@ -48,6 +49,12 @@ RecordComponent::RecordComponent() : BaseRecordComponent(NoInit())
 RecordComponent::RecordComponent(NoInit) : BaseRecordComponent(NoInit())
 {}
 
+RecordComponent::RecordComponent(BaseRecord<RecordComponent> const &baseRecord)
+    : BaseRecordComponent(NoInit())
+{
+    setData(baseRecord.m_recordComponentData);
+}
+
 // We need to instantiate this somewhere otherwise there might be linker issues
 // despite this thing actually being constepxr
 constexpr char const *const RecordComponent::SCALAR;

src/backend/MeshRecordComponent.cpp

@@ -19,6 +19,7 @@
  * If not, see <http://www.gnu.org/licenses/>.
  */
 #include "openPMD/backend/MeshRecordComponent.hpp"
+#include "openPMD/backend/BaseRecord.hpp"
 
 namespace openPMD
 {
@@ -28,6 +29,13 @@ MeshRecordComponent::MeshRecordComponent() : RecordComponent()
 MeshRecordComponent::MeshRecordComponent(NoInit) : RecordComponent(NoInit())
 {}
 
+MeshRecordComponent::MeshRecordComponent(
+    BaseRecord<MeshRecordComponent> const &baseRecord)
+    : RecordComponent(NoInit())
+{
+    setData(baseRecord.m_recordComponentData);
+}
+
 void MeshRecordComponent::read()
 {
     using DT = Datatype;

src/backend/PatchRecordComponent.cpp

@@ -20,6 +20,7 @@
  */
 #include "openPMD/backend/PatchRecordComponent.hpp"
 #include "openPMD/auxiliary/Memory.hpp"
+#include "openPMD/backend/BaseRecord.hpp"
 
 #include <algorithm>
 
@@ -74,6 +75,13 @@ Extent PatchRecordComponent::getExtent() const
     }
 }
 
+PatchRecordComponent::PatchRecordComponent(
+    BaseRecord<PatchRecordComponent> const &baseRecord)
+    : BaseRecordComponent(NoInit())
+{
+    setData(baseRecord.m_patchRecordComponentData);
+}
+
 PatchRecordComponent::PatchRecordComponent() : BaseRecordComponent(NoInit())
 {
     setData(std::make_shared<Data_t>());