diff --git a/src/App/Document.cpp b/src/App/Document.cpp
index b042326cf..b3b27b4b8 100644
--- a/src/App/Document.cpp
+++ b/src/App/Document.cpp
@@ -1894,15 +1894,14 @@ DocumentObject * Document::addObject(const char* sType, const char* pObjectName,
     string ObjectName;
     if (!base)
         return 0;
-    
-    App::DocumentObject* pcObject = dynamic_cast<App::DocumentObject*>(base);
-    if (!pcObject) {
+    if (!base->getTypeId().isDerivedFrom(App::DocumentObject::getClassTypeId())) {
         delete base;
         std::stringstream str;
         str << "'" << sType << "' is not a document object type";
         throw Base::TypeError(str.str());
     }
 
+    App::DocumentObject* pcObject = static_cast<App::DocumentObject*>(base);
     pcObject->setDocument(this);
 
     // do no transactions if we do a rollback!
diff --git a/src/App/DocumentObjectExtension.cpp b/src/App/DocumentObjectExtension.cpp
index 9976fde10..526bda776 100644
--- a/src/App/DocumentObjectExtension.cpp
+++ b/src/App/DocumentObjectExtension.cpp
@@ -37,7 +37,7 @@ EXTENSION_PROPERTY_SOURCE(App::DocumentObjectExtension, App::Extension)
 
 DocumentObjectExtension::DocumentObjectExtension() 
 {
-    initExtension(App::DocumentObjectExtension::getClassTypeId());
+    initExtension(App::DocumentObjectExtension::getExtensionClassTypeId());
 }
 
 DocumentObjectExtension::~DocumentObjectExtension()
diff --git a/src/App/Extension.cpp b/src/App/Extension.cpp
index d99f0b49a..0cf176d62 100644
--- a/src/App/Extension.cpp
+++ b/src/App/Extension.cpp
@@ -37,12 +37,17 @@
 /* We do not use a standart property macro for type initiation. The reason is that we have the first
  * PropertyData in the extension chain, there is no parent property data. 
  */
-TYPESYSTEM_SOURCE_P(App::Extension);
+EXTENSION_TYPESYSTEM_SOURCE_P(App::Extension);
 const App::PropertyData * App::Extension::extensionGetPropertyDataPtr(void){return &propertyData;}
 const App::PropertyData & App::Extension::extensionGetPropertyData(void) const{return propertyData;}
 App::PropertyData App::Extension::propertyData;
 void App::Extension::init(void){
-  initSubclass(App::Extension::classTypeId, "App::Extension" , "Base::Persistence", &(App::Extension::create) );
+
+    assert(Extension::classTypeId == Base::Type::badType() && "don't init() twice!");
+ 
+    /* Set up entry in the type system. */ 
+    Extension::classTypeId = Base::Type::createType(Base::Type::badType(), "App::Extension", 
+                                Extension::create); 
 }
 
 using namespace App;
@@ -161,6 +166,20 @@ void Extension::extensionGetPropertyMap(std::map< std::string, Property* >& Map)
     extensionGetPropertyData().getPropertyMap(this, Map);
 }
 
+void Extension::initExtensionSubclass(Base::Type& toInit, const char* ClassName, const char* ParentName, 
+                             Base::Type::instantiationMethod method) {
+
+    // dont't init twice!
+    assert(toInit == Base::Type::badType());
+    // get the parent class
+    Base::Type parentType(Base::Type::fromName(ParentName)); 
+    // forgot init parent!
+    assert(parentType != Base::Type::badType() );
+
+    // create the new type
+    toInit = Base::Type::createType(parentType, ClassName, method);
+}
+
 
 namespace App {
 EXTENSION_PROPERTY_SOURCE_TEMPLATE(App::ExtensionPython, App::ExtensionPython::Inherited)
diff --git a/src/App/Extension.h b/src/App/Extension.h
index 2ac4787ea..10816a14f 100644
--- a/src/App/Extension.h
+++ b/src/App/Extension.h
@@ -32,10 +32,44 @@
 namespace App {
     
 class ExtensionContainer;
+
+/// define Extension types
+#define EXTENSION_TYPESYSTEM_HEADER() \
+public: \
+  static Base::Type getExtensionClassTypeId(void); \
+  virtual Base::Type getExtensionTypeId(void) const; \
+  static void init(void);\
+  static void *create(void);\
+private: \
+  static Base::Type classTypeId
     
+/// define to implement a subclass of Base::BaseClass
+#define EXTENSION_TYPESYSTEM_SOURCE_P(_class_) \
+Base::Type _class_::getExtensionClassTypeId(void) { return _class_::classTypeId; } \
+Base::Type _class_::getExtensionTypeId(void) const { return _class_::classTypeId; } \
+Base::Type _class_::classTypeId = Base::Type::badType();  \
+void * _class_::create(void){\
+   return new _class_ ();\
+}
+
+/// define to implement a subclass of Base::BaseClass
+#define EXTENSION_TYPESYSTEM_SOURCE(_class_, _parentclass_) \
+EXTENSION_TYPESYSTEM_SOURCE_P(_class_);\
+void _class_::init(void){\
+  initExtensionSubclass(_class_::classTypeId, #_class_ , #_parentclass_, &(_class_::create) ); \
+}
+
+#define EXTENSION_TYPESYSTEM_SOURCE_TEMPLATE(_class_) \
+template<> Base::Type _class_::classTypeId = Base::Type::badType();  \
+template<> Base::Type _class_::getExtensionClassTypeId(void) { return _class_::classTypeId; } \
+template<> Base::Type _class_::getExtensionTypeId(void) const { return _class_::classTypeId; } \
+template<> void * _class_::create(void){\
+   return new _class_ ();\
+}
+
 // init property stuff
 #define EXTENSION_PROPERTY_HEADER(_class_) \
-  TYPESYSTEM_HEADER(); \
+  EXTENSION_TYPESYSTEM_HEADER(); \
 protected: \
   static const App::PropertyData * extensionGetPropertyDataPtr(void); \
   virtual const App::PropertyData &extensionGetPropertyData(void) const; \
@@ -43,22 +77,22 @@ private: \
   static App::PropertyData propertyData
 
 #define EXTENSION_PROPERTY_SOURCE(_class_, _parentclass_) \
-TYPESYSTEM_SOURCE_P(_class_);\
+EXTENSION_TYPESYSTEM_SOURCE_P(_class_);\
 const App::PropertyData * _class_::extensionGetPropertyDataPtr(void){return &propertyData;} \
 const App::PropertyData & _class_::extensionGetPropertyData(void) const{return propertyData;} \
 App::PropertyData _class_::propertyData; \
 void _class_::init(void){\
-  initSubclass(_class_::classTypeId, #_class_ , #_parentclass_, &(_class_::create) ); \
+  initExtensionSubclass(_class_::classTypeId, #_class_ , #_parentclass_, &(_class_::create) ); \
   _class_::propertyData.parentPropertyData = _parentclass_::extensionGetPropertyDataPtr();\
 }
 
 #define EXTENSION_PROPERTY_SOURCE_TEMPLATE(_class_, _parentclass_) \
-TYPESYSTEM_SOURCE_TEMPLATE(_class_);\
+EXTENSION_TYPESYSTEM_SOURCE_TEMPLATE(_class_);\
 template<> App::PropertyData _class_::propertyData = App::PropertyData(); \
 template<> const App::PropertyData * _class_::extensionGetPropertyDataPtr(void){return &propertyData;} \
 template<> const App::PropertyData & _class_::extensionGetPropertyData(void) const{return propertyData;} \
 template<> void _class_::init(void){\
-  initSubclass(_class_::classTypeId, #_class_ , #_parentclass_, &(_class_::create) ); \
+  initExtensionSubclass(_class_::classTypeId, #_class_ , #_parentclass_, &(_class_::create) ); \
   _class_::propertyData.parentPropertyData = _parentclass_::extensionGetPropertyDataPtr();\
 }
   
@@ -86,7 +120,7 @@ template<> void _class_::init(void){\
  * MyExtension::MyExtension() {
  * 
  *     EXTENSION_ADD_PROPERTY(MyProp, (0)) * 
- *     initExtension(MyExtension::getClassTypeId());
+ *     initExtension(MyExtension::getExtensionClassTypeId());
  * }
  * typedef ExtensionPythonT<MyExtension> MyExtensionPython;
  * @endcode 
@@ -161,7 +195,7 @@ template<> void _class_::init(void){\
  * exension creators responsibility to ensure full implementation.
  * 
  */
-class AppExport Extension : public virtual Base::Persistence
+class AppExport Extension
 {
 
     //The cass does not have properties itself, but it is important to provide the property access
@@ -210,6 +244,15 @@ public:
     /// get the Group of a named Property
     virtual const char* extensionGetPropertyDocumentation(const char *name) const;
     //@}
+    
+    /** @name TypeHandling */
+    //@{
+    bool isDerivedFrom(const Base::Type type) const {return getExtensionTypeId().isDerivedFrom(type);}
+protected:
+    static void initExtensionSubclass(Base::Type &toInit,const char* ClassName, const char *ParentName, 
+                             Base::Type::instantiationMethod method=0);
+    //@}
+
 
 protected:     
     void initExtension(Base::Type type);
diff --git a/src/App/ExtensionContainer.h b/src/App/ExtensionContainer.h
index 240c45c79..dc6e42b88 100644
--- a/src/App/ExtensionContainer.h
+++ b/src/App/ExtensionContainer.h
@@ -130,14 +130,14 @@ public:
     //returns first of type (or derived from) and throws otherwise
     template<typename ExtensionT>
     ExtensionT* getExtensionByType() {
-        return dynamic_cast<ExtensionT*>(getExtension(ExtensionT::getClassTypeId()));
+        return dynamic_cast<ExtensionT*>(getExtension(ExtensionT::getExtensionClassTypeId()));
     };
     
     //get all extensions which have the given base class
     std::vector<Extension*> getExtensionsDerivedFrom(Base::Type type) const;
     template<typename ExtensionT>
     std::vector<ExtensionT*> getExtensionsDerivedFromType() const {
-        auto vec = getExtensionsDerivedFrom(ExtensionT::getClassTypeId());
+        auto vec = getExtensionsDerivedFrom(ExtensionT::getExtensionClassTypeId());
         std::vector<ExtensionT*> typevec;
         for(auto ext : vec)
             typevec.push_back(dynamic_cast<ExtensionT*>(ext));
diff --git a/src/App/ExtensionContainerPyImp.cpp b/src/App/ExtensionContainerPyImp.cpp
index afe3e386c..627a70113 100644
--- a/src/App/ExtensionContainerPyImp.cpp
+++ b/src/App/ExtensionContainerPyImp.cpp
@@ -110,7 +110,7 @@ PyObject* ExtensionContainerPy::hasExtension(PyObject *args) {
 
     //get the extension type asked for
     Base::Type extension =  Base::Type::fromName(type);
-    if(extension.isBad() || !extension.isDerivedFrom(App::Extension::getClassTypeId())) {
+    if(extension.isBad() || !extension.isDerivedFrom(App::Extension::getExtensionClassTypeId())) {
         std::stringstream str;
         str << "No extension found of type '" << type << "'" << std::ends;
         throw Py::Exception(Base::BaseExceptionFreeCADError,str.str());
@@ -133,7 +133,7 @@ PyObject* ExtensionContainerPy::addExtension(PyObject *args) {
 
     //get the extension type asked for
     Base::Type extension =  Base::Type::fromName(type);
-    if(extension.isBad() || !extension.isDerivedFrom(App::Extension::getClassTypeId())) {
+    if(extension.isBad() || !extension.isDerivedFrom(App::Extension::getExtensionClassTypeId())) {
         std::stringstream str;
         str << "No extension found of type '" << type << "'" << std::ends;
         throw Py::Exception(Base::BaseExceptionFreeCADError,str.str());
diff --git a/src/App/GeoFeatureGroupExtension.cpp b/src/App/GeoFeatureGroupExtension.cpp
index 243aed3f7..d37b80ca2 100644
--- a/src/App/GeoFeatureGroupExtension.cpp
+++ b/src/App/GeoFeatureGroupExtension.cpp
@@ -45,7 +45,7 @@ EXTENSION_PROPERTY_SOURCE(App::GeoFeatureGroupExtension, App::GroupExtension)
 
 GeoFeatureGroupExtension::GeoFeatureGroupExtension(void)
 {
-    initExtension(GeoFeatureGroupExtension::getClassTypeId());
+    initExtension(GeoFeatureGroupExtension::getExtensionClassTypeId());
     
     EXTENSION_ADD_PROPERTY(Placement,(Base::Placement()));
 }
@@ -128,7 +128,7 @@ bool GeoFeatureGroupExtension::geoHasObject (const DocumentObject* obj) const {
 DocumentObject* GeoFeatureGroupExtension::getGroupOfObject(const DocumentObject* obj, bool indirect)
 {
     const Document* doc = obj->getDocument();
-    std::vector<DocumentObject*> grps = doc->getObjectsOfType(GeoFeatureGroupExtension::getClassTypeId());
+    std::vector<DocumentObject*> grps = doc->getObjectsOfType(GeoFeatureGroupExtension::getExtensionClassTypeId());
     for (std::vector<DocumentObject*>::const_iterator it = grps.begin(); it != grps.end(); ++it) {
         GeoFeatureGroupExtension* grp = (GeoFeatureGroupExtension*)(*it);
         if ( indirect ) {
diff --git a/src/App/GeoFeatureGroupExtension.h b/src/App/GeoFeatureGroupExtension.h
index f26382c62..31f22eb3d 100644
--- a/src/App/GeoFeatureGroupExtension.h
+++ b/src/App/GeoFeatureGroupExtension.h
@@ -71,7 +71,7 @@ public:
 
     /// Returns true if the given DocumentObject is DocumentObjectGroup but not GeoFeatureGroup
     static bool isNonGeoGroup(const DocumentObject* obj) {
-        return obj->hasExtension(GroupExtension::getClassTypeId());
+        return obj->hasExtension(GroupExtension::getExtensionClassTypeId());
     }
 };
 
diff --git a/src/App/GroupExtension.cpp b/src/App/GroupExtension.cpp
index 391fd7efb..dc6c518b6 100644
--- a/src/App/GroupExtension.cpp
+++ b/src/App/GroupExtension.cpp
@@ -38,7 +38,7 @@ EXTENSION_PROPERTY_SOURCE(App::GroupExtension, App::DocumentObjectExtension)
 
 GroupExtension::GroupExtension()
 {
-    initExtension(GroupExtension::getClassTypeId());
+    initExtension(GroupExtension::getExtensionClassTypeId());
     
     EXTENSION_ADD_PROPERTY_TYPE(Group,(0),"Base",(App::PropertyType)(Prop_Output),"List of referenced objects");
 }
@@ -96,8 +96,8 @@ void GroupExtension::removeObjectsFromDocument()
 void GroupExtension::removeObjectFromDocument(DocumentObject* obj)
 {
     // remove all children
-    if (obj->hasExtension(GroupExtension::getClassTypeId())) {
-        GroupExtension *grp = static_cast<GroupExtension*>(obj->getExtension(GroupExtension::getClassTypeId()));
+    if (obj->hasExtension(GroupExtension::getExtensionClassTypeId())) {
+        GroupExtension *grp = static_cast<GroupExtension*>(obj->getExtension(GroupExtension::getExtensionClassTypeId()));
 
         // recursive call to remove all subgroups
         grp->removeObjectsFromDocument();
@@ -120,8 +120,9 @@ bool GroupExtension::hasObject(const DocumentObject* obj, bool recursive) const
     for (std::vector<DocumentObject*>::const_iterator it = grp.begin(); it != grp.end(); ++it) {
         if (*it == obj) {
             return true;
-        } else if ( recursive && (*it)->hasExtension(GroupExtension::getClassTypeId()) ) {
-            App::GroupExtension *subGroup = static_cast<App::GroupExtension *> ((*it)->getExtension(GroupExtension::getClassTypeId()));
+        } else if ( recursive && (*it)->hasExtension(GroupExtension::getExtensionClassTypeId()) ) {
+            App::GroupExtension *subGroup = static_cast<App::GroupExtension *> (
+                                    (*it)->getExtension(GroupExtension::getExtensionClassTypeId()));
 
             if (subGroup->hasObject (obj, recursive)) {
                 return true;
@@ -138,8 +139,8 @@ bool GroupExtension::isChildOf(const GroupExtension* group) const
     for (std::vector<DocumentObject*>::const_iterator it = grp.begin(); it != grp.end(); ++it) {
         if (*it == getExtendedObject())
             return true;
-        if ((*it)->hasExtension(GroupExtension::getClassTypeId())) {
-            if (this->isChildOf(static_cast<GroupExtension*>((*it)->getExtension(GroupExtension::getClassTypeId()))))
+        if ((*it)->hasExtension(GroupExtension::getExtensionClassTypeId())) {
+            if (this->isChildOf(static_cast<GroupExtension*>((*it)->getExtension(GroupExtension::getExtensionClassTypeId()))))
 
                 return true;
         }
@@ -180,7 +181,7 @@ int GroupExtension::countObjectsOfType(const Base::Type& typeId) const
 DocumentObject* GroupExtension::getGroupOfObject(const DocumentObject* obj)
 {
     const Document* doc = obj->getDocument();
-    std::vector<DocumentObject*> grps = doc->getObjectsOfType(GroupExtension::getClassTypeId());
+    std::vector<DocumentObject*> grps = doc->getObjectsOfType(GroupExtension::getExtensionClassTypeId());
     for (std::vector<DocumentObject*>::const_iterator it = grps.begin(); it != grps.end(); ++it) {
         GroupExtension* grp = (GroupExtension*)(*it);
         if (grp->hasObject(obj))
diff --git a/src/App/GroupExtensionPyImp.cpp b/src/App/GroupExtensionPyImp.cpp
index c99a5a8a1..398dcfc30 100644
--- a/src/App/GroupExtensionPyImp.cpp
+++ b/src/App/GroupExtensionPyImp.cpp
@@ -76,7 +76,7 @@ PyObject*  GroupExtensionPy::addObject(PyObject *args)
         PyErr_SetString(Base::BaseExceptionFreeCADError, "Cannot add a group object to itself");
         return NULL;
     }
-    if (docObj->getDocumentObjectPtr()->hasExtension(GroupExtension::getClassTypeId())) {
+    if (docObj->getDocumentObjectPtr()->hasExtension(GroupExtension::getExtensionClassTypeId())) {
         App::GroupExtension* docGrp = docObj->getDocumentObjectPtr()->getExtensionByType<GroupExtension>();
         if (docGrp->hasObject(getGroupExtensionPtr()->getExtendedObject())) {
             PyErr_SetString(Base::BaseExceptionFreeCADError, "Cannot add a group object to a child group");
diff --git a/src/App/OriginGroupExtension.cpp b/src/App/OriginGroupExtension.cpp
index 302ea76b1..82acaa8c5 100644
--- a/src/App/OriginGroupExtension.cpp
+++ b/src/App/OriginGroupExtension.cpp
@@ -39,7 +39,7 @@ EXTENSION_PROPERTY_SOURCE(App::OriginGroupExtension, App::GeoFeatureGroupExtensi
 
 OriginGroupExtension::OriginGroupExtension () {
     
-    initExtension(OriginGroupExtension::getClassTypeId());
+    initExtension(OriginGroupExtension::getExtensionClassTypeId());
     
     EXTENSION_ADD_PROPERTY_TYPE ( Origin, (0), 0, App::Prop_Hidden, "Origin linked to the group" );
 }
@@ -67,9 +67,11 @@ App::Origin *OriginGroupExtension::getOrigin () const {
 
 App::DocumentObject *OriginGroupExtension::getGroupOfObject (const DocumentObject* obj, bool indirect) {
     const Document* doc = obj->getDocument();
-    std::vector<DocumentObject*> grps = doc->getObjectsWithExtension ( OriginGroupExtension::getClassTypeId() );
+    std::vector<DocumentObject*> grps = doc->getObjectsWithExtension ( OriginGroupExtension::getExtensionClassTypeId() );
     for (auto grpObj: grps) {
-        OriginGroupExtension* grp = dynamic_cast <OriginGroupExtension* >(grpObj->getExtension(OriginGroupExtension::getClassTypeId()));
+        OriginGroupExtension* grp = dynamic_cast <OriginGroupExtension* >(grpObj->getExtension(
+                                                    OriginGroupExtension::getExtensionClassTypeId()));
+        
         if(!grp) throw Base::TypeError("Wrong type in origin group extenion");
             
         if ( indirect ) {
diff --git a/src/App/PreCompiled.h b/src/App/PreCompiled.h
index 6c6545ae0..3729ed29d 100644
--- a/src/App/PreCompiled.h
+++ b/src/App/PreCompiled.h
@@ -33,7 +33,6 @@
 #pragma warning( disable : 4275 )
 #pragma warning( disable : 4503 )
 #pragma warning( disable : 4786 )  // specifier longer then 255 chars
-#pragma warning( disable : 4250 )  // virtual inheritance warning
 #endif
 
 
@@ -86,7 +85,6 @@
 #include <boost/filesystem/operations.hpp>
 #include <boost/filesystem/exception.hpp>
 
-
 #endif //_PreComp_
 
 #endif // APP_PRECOMPILED_H
diff --git a/src/App/PropertyContainer.cpp b/src/App/PropertyContainer.cpp
index 4b6156e95..e8a2a2d84 100644
--- a/src/App/PropertyContainer.cpp
+++ b/src/App/PropertyContainer.cpp
@@ -51,6 +51,7 @@ TYPESYSTEM_SOURCE(App::PropertyContainer,Base::Persistence);
 // here the implemataion! description should take place in the header file!
 PropertyContainer::PropertyContainer()
 {
+    propertyData.parentPropertyData = 0; 
 }
 
 PropertyContainer::~PropertyContainer()
diff --git a/src/App/PropertyContainer.h b/src/App/PropertyContainer.h
index 2003e0c56..d315d452e 100644
--- a/src/App/PropertyContainer.h
+++ b/src/App/PropertyContainer.h
@@ -101,7 +101,7 @@ struct AppExport PropertyData
 
 /** Base class of all classes with properties
  */
-class AppExport PropertyContainer: public virtual Base::Persistence
+class AppExport PropertyContainer: public Base::Persistence
 {
 
   TYPESYSTEM_HEADER();
@@ -271,27 +271,4 @@ template<> void _class_::init(void){\
 
 } // namespace App
 
-
-/**
- * Overload of freecads base class cast for all cases without any virtual inheritance
- */
-template<typename T> T * freecad_dynamic_cast(App::PropertyContainer* t)
-{
-    if (t && t->isDerivedFrom(T::getClassTypeId()))
-        return static_cast<T*>(t);
-    else
-        return nullptr;
-}
-
-/**
- * See explaination above
- */
-template<typename T> const T * freecad_dynamic_cast(const App::PropertyContainer* t)
-{
-    if (t && t->isDerivedFrom(T::getClassTypeId()))
-        return static_cast<const T*>(t);
-    else
-        return nullptr;
-}
-
 #endif // APP_PROPERTYCONTAINER_H
diff --git a/src/Base/BaseClass.h b/src/Base/BaseClass.h
index bfe49baa6..7183d6b6b 100644
--- a/src/Base/BaseClass.h
+++ b/src/Base/BaseClass.h
@@ -104,25 +104,29 @@ public:
 };
 
 /**
- * Template that works just like dynamic_cast, but expects the argument to
- * inherit from Base::BaseClass. Note thst for base class this is exactly the same as a dynamic_cast.
- * The reason for that is that it is not possible to static_cast base to anything in the inheritance 
- * chain after PropertyContainer. The reason for this is the used virtual inheritance.
- * However, the function can be overload for different cast between objects in the inheritnce
- * chain after PropertyContainer, for example from DocumentObject to all its derived types-
- *
- */
+  * Template that works just like dynamic_cast, but expects the argument to
+  * inherit from Base::BaseClass.
+  *
+  */
 template<typename T> T * freecad_dynamic_cast(Base::BaseClass * t)
 {
-    return dynamic_cast<T*>(t);
+    if (t && t->isDerivedFrom(T::getClassTypeId()))
+        return static_cast<T*>(t);
+    else
+        return 0;
 }
-
+ 
 /**
- * See explaination above
+ * Template that works just like dynamic_cast, but expects the argument to
+ * inherit from a const Base::BaseClass.
+ *
  */
 template<typename T> const T * freecad_dynamic_cast(const Base::BaseClass * t)
 {
-    return dynamic_cast<const T*>(t);
+    if (t && t->isDerivedFrom(T::getClassTypeId()))
+        return static_cast<const T*>(t);
+    else
+        return 0;
 }
 
 
diff --git a/src/Base/Persistence.h b/src/Base/Persistence.h
index 1b92e9c6e..f3901153b 100644
--- a/src/Base/Persistence.h
+++ b/src/Base/Persistence.h
@@ -48,7 +48,7 @@ public:
      * It is not meant to have the exact size, it is more or less an estimation
      * which runs fast! Is it two bytes or a GB?
      */
-    virtual unsigned int getMemSize (void) const;
+    virtual unsigned int getMemSize (void) const = 0;
     /** This method is used to save properties to an XML document.
      * A good example you'll find in PropertyStandard.cpp, e.g. the vector:
      * \code
@@ -65,7 +65,7 @@ public:
      * is written. This means closing tags and writing UTF-8. 
      * @see Base::Writer
      */
-    virtual void Save (Writer &/*writer*/) const;
+    virtual void Save (Writer &/*writer*/) const = 0;
     /** This method is used to restore properties from an XML document.
      * It uses the XMLReader class, which bases on SAX, to read the in Save() 
      * written information. Again the Vector as an example:
@@ -81,7 +81,7 @@ public:
      * }
      * \endcode
      */
-    virtual void Restore(XMLReader &/*reader*/);
+    virtual void Restore(XMLReader &/*reader*/) = 0;
     /** This method is used to save large amounts of data to a binary file.
      * Sometimes it makes no sense to write property data as XML. In case the 
      * amount of data is too big or the data type has a more effective way to 
diff --git a/src/Gui/Application.cpp b/src/Gui/Application.cpp
index 56ff1f040..913131ce4 100644
--- a/src/Gui/Application.cpp
+++ b/src/Gui/Application.cpp
@@ -277,27 +277,27 @@ FreeCADGui_subgraphFromObject(PyObject * /*self*/, PyObject *args)
     SoNode* node = 0;
     try {
         Base::BaseClass* base = static_cast<Base::BaseClass*>(Base::Type::createInstanceByName(vp.c_str(), true));
-        //throws if dynamic_cast fails, hence no check needed
-        std::unique_ptr<Gui::ViewProviderDocumentObject> vp(dynamic_cast<Gui::ViewProviderDocumentObject*>(base));
+        if (base && base->getTypeId().isDerivedFrom(Gui::ViewProviderDocumentObject::getClassTypeId())) {
+            std::unique_ptr<Gui::ViewProviderDocumentObject> vp(static_cast<Gui::ViewProviderDocumentObject*>(base));
+            std::map<std::string, App::Property*> Map;
+            obj->getPropertyMap(Map);
+            vp->attach(obj);
+            for (std::map<std::string, App::Property*>::iterator it = Map.begin(); it != Map.end(); ++it) {
+                vp->updateData(it->second);
+            }
 
-        std::map<std::string, App::Property*> Map;
-        obj->getPropertyMap(Map);
-        vp->attach(obj);
-        for (std::map<std::string, App::Property*>::iterator it = Map.begin(); it != Map.end(); ++it) {
-            vp->updateData(it->second);
+            std::vector<std::string> modes = vp->getDisplayModes();
+            if (!modes.empty())
+                vp->setDisplayMode(modes.front().c_str());
+            node = vp->getRoot()->copy();
+            node->ref();
+            std::string type = "So";
+            type += node->getTypeId().getName().getString();
+            type += " *";
+            PyObject* proxy = 0;
+            proxy = Base::Interpreter().createSWIGPointerObj("pivy.coin", type.c_str(), (void*)node, 1);
+            return Py::new_reference_to(Py::Object(proxy, true));
         }
-
-        std::vector<std::string> modes = vp->getDisplayModes();
-        if (!modes.empty())
-            vp->setDisplayMode(modes.front().c_str());
-        node = vp->getRoot()->copy();
-        node->ref();
-        std::string type = "So";
-        type += node->getTypeId().getName().getString();
-        type += " *";
-        PyObject* proxy = 0;
-        proxy = Base::Interpreter().createSWIGPointerObj("pivy.coin", type.c_str(), (void*)node, 1);
-        return Py::new_reference_to(Py::Object(proxy, true));
     }
     catch (const Base::Exception& e) {
         if (node) node->unref();
diff --git a/src/Gui/Document.cpp b/src/Gui/Document.cpp
index feaf339df..a8bbe86b6 100644
--- a/src/Gui/Document.cpp
+++ b/src/Gui/Document.cpp
@@ -420,10 +420,9 @@ void Document::slotNewObject(const App::DocumentObject& Obj)
         setModified(true);
         Base::BaseClass* base = static_cast<Base::BaseClass*>(Base::Type::createInstanceByName(cName.c_str(),true));
         if (base) {
-            pcProvider = dynamic_cast<ViewProviderDocumentObject*>(base);
             // type not derived from ViewProviderDocumentObject!!!
-            assert(pcProvider);
-            
+            assert(base->getTypeId().isDerivedFrom(Gui::ViewProviderDocumentObject::getClassTypeId()));
+            pcProvider = static_cast<ViewProviderDocumentObject*>(base);
             d->_ViewProviderMap[&Obj] = pcProvider;
 
             try {
diff --git a/src/Gui/TreeView.cpp b/src/Gui/TreeView.cpp
index 1dd44aba3..3c708c4c9 100644
--- a/src/Gui/TreeView.cpp
+++ b/src/Gui/TreeView.cpp
@@ -71,9 +71,8 @@ void TreeView::mouseDoubleClickEvent (QMouseEvent * event)
         if (!view) return;
         getMainWindow()->setActiveWindow(view);
     }
-    else {
-        auto* vp = dynamic_cast<ViewProvider*>(item);
-        if (vp && vp->doubleClicked() == false)
+    else if (item->getTypeId().isDerivedFrom(ViewProvider::getClassTypeId())) {
+        if (static_cast<ViewProvider*>(item)->doubleClicked() == false)
             QTreeView::mouseDoubleClickEvent(event);
     }
 }
diff --git a/src/Gui/ViewProviderExtension.cpp b/src/Gui/ViewProviderExtension.cpp
index 2ee8d94c7..67b61af9a 100644
--- a/src/Gui/ViewProviderExtension.cpp
+++ b/src/Gui/ViewProviderExtension.cpp
@@ -37,7 +37,7 @@ EXTENSION_PROPERTY_SOURCE(Gui::ViewProviderExtension, App::Extension)
 
 ViewProviderExtension::ViewProviderExtension() 
 {
-    initExtension(Gui::ViewProviderExtension::getClassTypeId());
+    initExtension(Gui::ViewProviderExtension::getExtensionClassTypeId());
 }
 
 ViewProviderExtension::~ViewProviderExtension()
diff --git a/src/Gui/ViewProviderGeoFeatureGroupExtension.cpp b/src/Gui/ViewProviderGeoFeatureGroupExtension.cpp
index 6217b1b8d..6f025e64b 100644
--- a/src/Gui/ViewProviderGeoFeatureGroupExtension.cpp
+++ b/src/Gui/ViewProviderGeoFeatureGroupExtension.cpp
@@ -38,7 +38,7 @@ EXTENSION_PROPERTY_SOURCE(Gui::ViewProviderGeoFeatureGroupExtension, Gui::ViewPr
 
 ViewProviderGeoFeatureGroupExtension::ViewProviderGeoFeatureGroupExtension()
 {
-    initExtension(ViewProviderGeoFeatureGroupExtension::getClassTypeId());
+    initExtension(ViewProviderGeoFeatureGroupExtension::getExtensionClassTypeId());
     
     pcGroupChildren = new SoGroup();
     pcGroupChildren->ref();
diff --git a/src/Gui/ViewProviderGroupExtension.cpp b/src/Gui/ViewProviderGroupExtension.cpp
index 3def916dc..a86b98a3c 100644
--- a/src/Gui/ViewProviderGroupExtension.cpp
+++ b/src/Gui/ViewProviderGroupExtension.cpp
@@ -44,7 +44,7 @@ EXTENSION_PROPERTY_SOURCE(Gui::ViewProviderGroupExtension, Gui::ViewProviderExte
 
 ViewProviderGroupExtension::ViewProviderGroupExtension()  : visible(false)
 {
-    initExtension(ViewProviderGroupExtension::getClassTypeId());
+    initExtension(ViewProviderGroupExtension::getExtensionClassTypeId());
     
 }
 
@@ -83,7 +83,7 @@ bool ViewProviderGroupExtension::extensionCanDropObject(App::DocumentObject* obj
         return false;  
     
     //group into group?
-    if (obj->hasExtension(App::GroupExtension::getClassTypeId()))
+    if (obj->hasExtension(App::GroupExtension::getExtensionClassTypeId()))
             if (group->isChildOf(obj->getExtensionByType<App::GroupExtension>()))
                 return false;
     
diff --git a/src/Gui/ViewProviderOriginGroupExtension.cpp b/src/Gui/ViewProviderOriginGroupExtension.cpp
index f19ae9655..a5cb7edad 100644
--- a/src/Gui/ViewProviderOriginGroupExtension.cpp
+++ b/src/Gui/ViewProviderOriginGroupExtension.cpp
@@ -48,7 +48,7 @@ EXTENSION_PROPERTY_SOURCE(Gui::ViewProviderOriginGroupExtension, Gui::ViewProvid
 
 ViewProviderOriginGroupExtension::ViewProviderOriginGroupExtension()
 {
-    initExtension(ViewProviderOriginGroupExtension::getClassTypeId());
+    initExtension(ViewProviderOriginGroupExtension::getExtensionClassTypeId());
 }
 
 ViewProviderOriginGroupExtension::~ViewProviderOriginGroupExtension()
diff --git a/src/Mod/PartDesign/Gui/Utils.cpp b/src/Mod/PartDesign/Gui/Utils.cpp
index ad285b0be..ee97e0811 100644
--- a/src/Mod/PartDesign/Gui/Utils.cpp
+++ b/src/Mod/PartDesign/Gui/Utils.cpp
@@ -238,8 +238,8 @@ bool isPartDesignAwareObjecta (App::DocumentObject *obj, bool respectGroups = fa
             PartDesign::Body::isAllowed ( obj ) ||
             obj->isDerivedFrom ( PartDesign::Body::getClassTypeId () ) ||
             ( respectGroups && (
-                                obj->hasExtension (App::GeoFeatureGroupExtension::getClassTypeId () ) ||
-                                obj->hasExtension (App::GroupExtension::getClassTypeId () )
+                                obj->hasExtension (App::GeoFeatureGroupExtension::getExtensionClassTypeId () ) ||
+                                obj->hasExtension (App::GroupExtension::getExtensionClassTypeId () )
                                ) ) );
 }