ObjDefManager: Set replacement object's handle info after calling set()

Make gamedef optional when constructing an ObjDefManager
Add note about object ownership

src/mapgen.cpp

@@ -434,7 +434,7 @@ void GenerateNotifier::getEvents(
 ObjDefManager::ObjDefManager(IGameDef *gamedef, ObjDefType type)
 {
 	m_objtype = type;
-	m_ndef = gamedef->getNodeDefManager();
+	m_ndef = gamedef ? gamedef->getNodeDefManager() : NULL;
 }
 
 
@@ -471,7 +471,16 @@ ObjDef *ObjDefManager::get(ObjDefHandle handle) const
 ObjDef *ObjDefManager::set(ObjDefHandle handle, ObjDef *obj)
 {
 	u32 index = validateHandle(handle);
-	return (index != OBJDEF_INVALID_INDEX) ? setRaw(index, obj) : NULL;
+	if (index == OBJDEF_INVALID_INDEX)
+		return NULL;
+
+	ObjDef *oldobj = setRaw(index, obj);
+
+	obj->uid    = oldobj->uid;
+	obj->index  = oldobj->index;
+	obj->handle = oldobj->handle;
+
+	return oldobj;
 }
 
 

src/mapgen.h

@@ -206,12 +206,15 @@ class ObjDef {
 	std::string name;
 };
 
+// WARNING: Ownership of ObjDefs is transferred to the ObjDefManager it is
+// added/set to.  Note that ObjDefs managed by ObjDefManager are NOT refcounted,
+// so the same ObjDef instance must not be referenced multiple
 class ObjDefManager {
 public:
 	ObjDefManager(IGameDef *gamedef, ObjDefType type);
 	virtual ~ObjDefManager();
 
-	virtual const char *getObjectTitle() const = 0;
+	virtual const char *getObjectTitle() const { return "ObjDef"; }
 
 	virtual void clear();
 	virtual ObjDef *getByName(const std::string &name) const;