[wip] partially working implementation

include/openPMD/backend/Attributable.hpp

@@ -127,7 +127,7 @@ class Attributable
     friend class BaseRecord;
     template< typename T_elem >
     friend class BaseRecordInterface;
-    template< typename >
+    template< typename, typename >
     friend class internal::BaseRecordData;
     template<
         typename T,

include/openPMD/backend/BaseRecord.hpp

@@ -142,6 +142,12 @@ 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;
@@ -178,6 +184,8 @@ class BaseRecord :
 protected:
     void readBase();
 
+    void datasetDefined() override;
+
 private:
     void flush(std::string const&) final;
     virtual void flush_impl(std::string const&) = 0;
@@ -238,12 +246,11 @@ BaseRecord< T_elem, T_RecordComponent >::operator[]( key_type const & key )
             throw std::runtime_error("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;
     }
 }
@@ -263,12 +270,12 @@ BaseRecord< T_elem, T_RecordComponent >::operator[](key_type&& key)
             throw std::runtime_error("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;
     }
 }
@@ -417,4 +424,18 @@ 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

@@ -133,6 +133,8 @@ class BaseRecordComponent : public Attributable
 
     BaseRecordComponent( std::shared_ptr< internal::BaseRecordComponentData > );
 
+    virtual void datasetDefined();
+
 private:
     BaseRecordComponent();
 }; // BaseRecordComponent

include/openPMD/backend/MeshRecordComponent.hpp

@@ -86,6 +86,9 @@ class MeshRecordComponent : public RecordComponent
      */
     template< typename T >
     MeshRecordComponent& makeConstant(T);
+
+protected:
+    void datasetDefined() override;
 };
 
 

src/Mesh.cpp

@@ -237,11 +237,8 @@ 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
             {
                 Parameter< Operation::CREATE_PATH > pCreate;
@@ -257,8 +254,6 @@ 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

@@ -93,6 +93,8 @@ 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(
@@ -186,6 +188,7 @@ 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::resetDatatype(Datatype d)
     if( written() )
         throw std::runtime_error("A Records Datatype can not (yet) be changed after it has been written.");
 
+    datasetDefined();
     get().m_dataset.dtype = d;
     return *this;
 }
@@ -79,4 +80,7 @@ BaseRecordComponent::BaseRecordComponent()
 {
     Attributable::setData( m_baseRecordComponentData );
 }
+
+void BaseRecordComponent::datasetDefined()
+{}
 } // namespace openPMD

src/backend/MeshRecordComponent.cpp

@@ -25,9 +25,7 @@ namespace openPMD
 {
 MeshRecordComponent::MeshRecordComponent()
         : RecordComponent()
-{
-    setPosition(std::vector< double >{0});
-}
+{}
 
 void
 MeshRecordComponent::read()
@@ -62,6 +60,12 @@ 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);

src/backend/PatchRecordComponent.cpp

@@ -53,6 +53,7 @@ PatchRecordComponent::resetDataset(Dataset d)
                     [](Extent::value_type const& i) { return i == 0u; }) )
         throw std::runtime_error("Dataset extent must not be zero in any dimension.");
 
+    datasetDefined();
     get().m_dataset = d;
     dirty() = true;
     return *this;