populate_derived() upon instance creation, don't only rely on serialization 'hack' #5364

src/ifcopenshell-python/ifcopenshell/express/templates.py

@@ -210,7 +210,7 @@ entity_implementation = """// Function implementations for %(name)s
 const IfcParse::entity& %(schema_name)s::%(name)s::declaration() const { return *((IfcParse::entity*)%(schema_name_upper)s_types[%(index_in_schema)d]); }
 const IfcParse::entity& %(schema_name)s::%(name)s::Class() { return *((IfcParse::entity*)%(schema_name_upper)s_types[%(index_in_schema)d]); }
 %(schema_name)s::%(name)s::%(name)s(IfcEntityInstanceData&& e) : %(superclass)s { }
-%(schema_name)s::%(name)s::%(name)s(%(constructor_arguments)s) : %(superclass_num_attrs)s { %(constructor_implementation)s }
+%(schema_name)s::%(name)s::%(name)s(%(constructor_arguments)s) : %(superclass_num_attrs)s { %(constructor_implementation)s; populate_derived(); }
 """
 
 # data_ = e; 

src/ifcparse/IfcBaseClass.h

@@ -139,7 +139,7 @@ class IFC_PARSE_API IfcLateBoundEntity : public IfcBaseClass {
 
 class IFC_PARSE_API IfcBaseEntity : public IfcBaseClass {
   public:
-    IfcBaseEntity(IfcEntityInstanceData&& data) : IfcBaseClass(std::move(data)) {}
+    IfcBaseEntity(IfcEntityInstanceData&& data);
 
     IfcBaseEntity(size_t n)
         : IfcBaseClass(IfcEntityInstanceData(storage_t(n)))
@@ -158,6 +158,8 @@ class IFC_PARSE_API IfcBaseEntity : public IfcBaseClass {
     boost::shared_ptr<aggregate_of_instance> get_inverse(const std::string& name) const;
 
     unsigned set_id(const boost::optional<unsigned>& i);
+
+    void populate_derived();
 };
 
 // TODO: Investigate whether these should be template classes instead

src/ifcparse/IfcUtil.cpp

@@ -202,11 +202,20 @@ void IfcUtil::unescape_xml(std::string& str) {
     boost::replace_all(str, ">", ">");
 }
 
-/*
-Argument* IfcUtil::IfcBaseEntity::get(const std::string& name) const {
-    return data().getArgument(declaration().attribute_index(name));
+IfcUtil::IfcBaseEntity::IfcBaseEntity(IfcEntityInstanceData&& data)
+    : IfcBaseClass(std::move(data))
+{}
+
+void IfcUtil::IfcBaseEntity::populate_derived() {
+    for (auto it = declaration().derived().begin(); it != declaration().derived().end(); ++it) {
+        if (*it) {
+            this->data().storage_.set(
+                std::distance(declaration().derived().begin(), it),
+                Derived{}
+            );
+        }
+    }
 }
-*/
 
 AttributeValue IfcUtil::IfcBaseEntity::get(const std::string& name) const
 {

src/ifcwrap/IfcParseWrapper.i

@@ -596,7 +596,11 @@ static IfcUtil::ArgumentType helper_fn_attribute_type(const IfcUtil::IfcBaseClas
 		const IfcParse::schema_definition* schema = IfcParse::schema_by_name(schema_identifier);
 		const IfcParse::declaration* decl = schema->declaration_by_name(name);
         IfcEntityInstanceData data(storage_t(decl->as_entity() ? decl->as_entity()->attribute_count() : 1));
-		return schema->instantiate(decl, std::move(data));
+		auto inst = schema->instantiate(decl, std::move(data));
+		if (auto entinst = inst->as<IfcUtil::IfcBaseEntity>()) {
+            entinst->populate_derived();
+        }
+		return inst;
 	}
 %}