[wip] partially working implementation

include/openPMD/backend/Attributable.hpp

@@ -122,7 +122,7 @@ class Attributable
     template <typename T_elem, typename T_RecordComponent>
     friend class BaseRecord;
     template <typename T_elem> friend class BaseRecordInterface;
-    template <typename> friend class internal::BaseRecordData;
+    template <typename, typename> friend class internal::BaseRecordData;
     template <
         typename T,
         typename T_key,

include/openPMD/backend/BaseRecord.hpp

@@ -138,6 +138,12 @@ class BaseRecord
     using iterator = typename T_container::iterator;
     using const_iterator = typename T_container::const_iterator;
 
+    // this avoids object slicing
+    operator T_RecordComponent() const
+    {
+        return {m_baseRecordData};
+    }
+
     virtual ~BaseRecord() = default;
 
     mapped_type &operator[](key_type const &key) override;
@@ -176,6 +182,8 @@ class BaseRecord
 protected:
     void readBase();
 
+    void datasetDefined() override;
+
 private:
     void flush(std::string const &) final;
     virtual void flush_impl(std::string const &) = 0;
@@ -235,12 +243,11 @@ BaseRecord<T_elem, T_RecordComponent>::operator[](key_type const &key)
                 "A scalar component can not be contained at "
                 "the same time as one or more regular components.");
 
-        mapped_type &ret = T_container::operator[](key);
         if (keyScalar)
         {
-            get().m_containsScalar = true;
-            ret.parent() = this->parent();
+            datasetDefined();
         }
+        mapped_type &ret = keyScalar ? *this : T_container::operator[](key);
         return ret;
     }
 }
@@ -261,12 +268,12 @@ inline auto BaseRecord<T_elem, T_RecordComponent>::operator[](key_type &&key)
                 "A scalar component can not be contained at "
                 "the same time as one or more regular components.");
 
-        mapped_type &ret = T_container::operator[](std::move(key));
         if (keyScalar)
         {
-            get().m_containsScalar = true;
-            ret.parent() = this->parent();
+            datasetDefined();
         }
+        mapped_type &ret =
+            keyScalar ? *this : T_container::operator[](std::move(key));
         return ret;
     }
 }
@@ -421,4 +428,18 @@ inline bool BaseRecord<T_elem, T_RecordComponent>::dirtyRecursive() const
     }
     return false;
 }
+
+template <typename T_elem, typename T_RecordComponent>
+void BaseRecord<T_elem, T_RecordComponent>::datasetDefined()
+{
+    // If the RecordComponent API of this object has been used, then the record
+    // is a scalar one
+    T_container::emplace(
+        RecordComponent::SCALAR,
+        // need to construct it in this line already, construction inside
+        // emplace is impossible due to private constructors
+        T_RecordComponent{m_baseRecordData});
+    get().m_containsScalar = true;
+    T_RecordComponent::datasetDefined();
+}
 } // namespace openPMD

include/openPMD/backend/BaseRecordComponent.hpp

@@ -125,6 +125,8 @@ class BaseRecordComponent : public Attributable
 
     BaseRecordComponent(std::shared_ptr<internal::BaseRecordComponentData>);
 
+    virtual void datasetDefined();
+
 private:
     BaseRecordComponent();
 }; // BaseRecordComponent

include/openPMD/backend/MeshRecordComponent.hpp

@@ -79,6 +79,9 @@ class MeshRecordComponent : public RecordComponent
      * @return A reference to this RecordComponent.
      */
     template <typename T> MeshRecordComponent &makeConstant(T);
+
+protected:
+    void datasetDefined() override;
 };
 
 template <typename T> std::vector<T> MeshRecordComponent::position() const

src/Mesh.cpp

@@ -226,12 +226,8 @@ void Mesh::flush_impl(std::string const &name)
             if (scalar())
             {
                 MeshRecordComponent &mrc = at(RecordComponent::SCALAR);
-                mrc.parent() = parent();
                 mrc.flush(name);
                 IOHandler()->flush();
-                writable().abstractFilePosition =
-                    mrc.writable().abstractFilePosition;
-                written() = true;
             }
             else
             {
@@ -248,8 +244,6 @@ void Mesh::flush_impl(std::string const &name)
             for (auto &comp : *this)
             {
                 comp.second.flush(name);
-                writable().abstractFilePosition =
-                    comp.second.writable().abstractFilePosition;
             }
         }
         else

src/RecordComponent.cpp

@@ -88,6 +88,8 @@ RecordComponent &RecordComponent::resetDataset(Dataset d)
         throw error::WrongAPIUsage(
             "[RecordComponent] Must set specific datatype.");
     }
+
+    datasetDefined();
     // if( d.extent.empty() )
     //    throw std::runtime_error("Dataset extent must be at least 1D.");
     if (std::any_of(
@@ -176,6 +178,7 @@ RecordComponent &RecordComponent::makeEmpty(Dataset d)
     if (rc.m_dataset.extent.size() == 0)
         throw std::runtime_error("Dataset extent must be at least 1D.");
 
+    datasetDefined();
     rc.m_isEmpty = true;
     dirty() = true;
     if (!written())

src/backend/BaseRecordComponent.cpp

@@ -35,6 +35,7 @@ BaseRecordComponent &BaseRecordComponent::resetDatatype(Datatype d)
             "A Records Datatype can not (yet) be changed after it has been "
             "written.");
 
+    datasetDefined();
     get().m_dataset.dtype = d;
     return *this;
 }
@@ -74,4 +75,7 @@ BaseRecordComponent::BaseRecordComponent() : Attributable{nullptr}
 {
     Attributable::setData(m_baseRecordComponentData);
 }
+
+void BaseRecordComponent::datasetDefined()
+{}
 } // namespace openPMD

src/backend/MeshRecordComponent.cpp

@@ -23,9 +23,7 @@
 namespace openPMD
 {
 MeshRecordComponent::MeshRecordComponent() : RecordComponent()
-{
-    setPosition(std::vector<double>{0});
-}
+{}
 
 void MeshRecordComponent::read()
 {
@@ -61,6 +59,12 @@ MeshRecordComponent &MeshRecordComponent::setPosition(std::vector<T> pos)
     return *this;
 }
 
+void MeshRecordComponent::datasetDefined()
+{
+    setPosition(std::vector<double>{0});
+    RecordComponent::datasetDefined();
+}
+
 template MeshRecordComponent &
 MeshRecordComponent::setPosition(std::vector<float> pos);
 template MeshRecordComponent &

src/backend/PatchRecordComponent.cpp

@@ -55,6 +55,7 @@ PatchRecordComponent &PatchRecordComponent::resetDataset(Dataset d)
         throw std::runtime_error(
             "Dataset extent must not be zero in any dimension.");
 
+    datasetDefined();
     get().m_dataset = d;
     dirty() = true;
     return *this;