diff --git a/src/ifcopenshell-python/ifcopenshell/express/implementation.py b/src/ifcopenshell-python/ifcopenshell/express/implementation.py
index b19e2cf23a..b7f87b4b2f 100644
--- a/src/ifcopenshell-python/ifcopenshell/express/implementation.py
+++ b/src/ifcopenshell-python/ifcopenshell/express/implementation.py
@@ -153,6 +153,8 @@ class Implementation(codegen.Base):
                             return templates.set_attr_stmt_enum
                         elif arg["is_templated_list"] and not (select or simple or express):
                             return templates.set_attr_stmt_array
+                        elif arg["full_type"].endswith('*'):
+                            return templates.set_attr_instance
                         else:
                             return templates.set_attr_stmt
 
@@ -172,6 +174,7 @@ class Implementation(codegen.Base):
                             "non_optional_type": arg["non_optional_type"].replace("::Value", ""),
                             "star_if_optional": "*" if "boost::optional" in arg["full_type"] else "",
                             "check_optional_set_begin": "if (v) {" if "boost::optional" in arg["full_type"] else "",
+                            "check_optional_set_else": "} else {" if "boost::optional" in arg["full_type"] else "if constexpr (false)",
                             "check_optional_set_end": "}" if "boost::optional" in arg["full_type"] else "",
                         },
                     )
@@ -188,6 +191,8 @@ class Implementation(codegen.Base):
                         if arg["is_templated_list"]
                         else templates.constructor_stmt_enum
                         if arg["is_enum"]
+                        else templates.constructor_stmt_instance
+                        if arg["full_type"].endswith('*')
                         else templates.constructor_stmt
                     )
                     impl = tmpl % {
diff --git a/src/ifcopenshell-python/ifcopenshell/express/templates.py b/src/ifcopenshell-python/ifcopenshell/express/templates.py
index 920fc70bbe..487c737518 100644
--- a/src/ifcopenshell-python/ifcopenshell/express/templates.py
+++ b/src/ifcopenshell-python/ifcopenshell/express/templates.py
@@ -128,10 +128,9 @@ simpletype_impl_type = "return *((IfcParse::type_declaration*)%(schema_name_uppe
 simpletype_impl_class = "return *((IfcParse::type_declaration*)%(schema_name_upper)s_types[%(index_in_schema)d]);"
 simpletype_impl_explicit_constructor = "data_ = e;"
 simpletype_impl_constructor = (
-    "data_ = new IfcEntityInstanceData(%(schema_name_upper)s_types[%(index_in_schema)d]); {IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument(); attr->set(v"
-    + "); data_->setArgument(0, attr);}"
+    "data_ = new IfcEntityInstanceData(%(schema_name_upper)s_types[%(index_in_schema)d]); set_value(0, v);"
 )
-simpletype_impl_constructor_templated = "data_ = new IfcEntityInstanceData(%(schema_name_upper)s_types[%(index_in_schema)d]); {IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument(); attr->set(v->generalize()); data_->setArgument(0, attr);}"
+simpletype_impl_constructor_templated = "data_ = new IfcEntityInstanceData(%(schema_name_upper)s_types[%(index_in_schema)d]); set_value(0, v->generalize());"
 simpletype_impl_cast = "return *data_->getArgument(0);"
 simpletype_impl_cast_templated = (
     "aggregate_of_instance::ptr es = *data_->getArgument(0); return es->as< %(underlying_type)s >();"
@@ -187,16 +186,12 @@ const IfcParse::enumeration_type& %(schema_name)s::%(name)s::Class() { return *(
 
 %(schema_name)s::%(name)s::%(name)s(Value v) {
     data_ = new IfcEntityInstanceData(%(schema_name_upper)s_types[%(index_in_schema)d]);
-    IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();
-    attr->set(IfcWrite::IfcWriteArgument::EnumerationReference(v,ToString(v)));
-    data_->setArgument(0,attr);
+    set_value(0, IfcWrite::IfcWriteArgument::EnumerationReference(v,ToString(v)));
 }
 
 %(schema_name)s::%(name)s::%(name)s(const std::string& v) {
     data_ = new IfcEntityInstanceData(%(schema_name_upper)s_types[%(index_in_schema)d]);
-    IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();
-    attr->set(IfcWrite::IfcWriteArgument::EnumerationReference(FromString(v),ToString(FromString(v))));
-    data_->setArgument(0,attr);
+    set_value(0, IfcWrite::IfcWriteArgument::EnumerationReference(FromString(v),ToString(FromString(v))));
 }
 
 const char* %(schema_name)s::%(name)s::ToString(Value v) {
@@ -217,7 +212,7 @@ entity_implementation = """// Function implementations for %(name)s
 %(inverse)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 { if (!e) return; if (e->type() != %(schema_name_upper)s_types[%(index_in_schema)d]) throw IfcException("Unable to find keyword in schema"); data_ = e; }
+%(schema_name)s::%(name)s::%(name)s(IfcEntityInstanceData* e) : %(superclass)s { data_ = e; }
 %(schema_name)s::%(name)s::%(name)s(%(constructor_arguments)s) : %(superclass)s {data_ = new IfcEntityInstanceData(%(schema_name_upper)s_types[%(index_in_schema)d]); %(constructor_implementation)s }
 """
 
@@ -257,33 +252,33 @@ get_attr_stmt_nested_array = "%(null_check)s aggregate_of_aggregate_of_instance:
 get_inverse = "return data_->getInverse(%(schema_name_upper)s_types[%(type_index)d], %(index)d)->as<%(type)s>();"
 
 set_attr_stmt = (
-    "{IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();%(check_optional_set_begin)sattr->set(%(star_if_optional)sv"
-    + ");%(check_optional_set_end)sdata_->setArgument(%(index)d,attr);}"
+    "%(check_optional_set_begin)sset_value(%(index)d, %(star_if_optional)sv);%(check_optional_set_else)sunset_value(%(index)d);%(check_optional_set_end)s"
 )
-set_attr_stmt_enum = "{IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();%(check_optional_set_begin)sattr->set(IfcWrite::IfcWriteArgument::EnumerationReference(%(star_if_optional)sv,%(non_optional_type)s::ToString(%(star_if_optional)sv)));%(check_optional_set_end)sdata_->setArgument(%(index)d,attr);}"
+set_attr_instance = (
+    "%(check_optional_set_begin)sset_value(%(index)d, v->as<IfcUtil::IfcBaseClass>());%(check_optional_set_else)sunset_value(%(index)d);%(check_optional_set_end)s"
+)
+set_attr_stmt_enum =  "%(check_optional_set_begin)sset_value(%(index)d, IfcWrite::IfcWriteArgument::EnumerationReference(%(star_if_optional)sv,%(non_optional_type)s::ToString(%(star_if_optional)sv)));%(check_optional_set_else)sunset_value(%(index)d);%(check_optional_set_end)s"
 set_attr_stmt_array = (
-    "{IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();%(check_optional_set_begin)sattr->set((%(star_if_optional)sv)->generalize()"
-    + ");%(check_optional_set_end)sdata_->setArgument(%(index)d,attr);}"
+    "%(check_optional_set_begin)sset_value(%(index)d, (%(star_if_optional)sv)->generalize());%(check_optional_set_else)sunset_value(%(index)d);%(check_optional_set_end)s"
 )
 
 constructor_stmt = (
-    "{IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();attr->set((%(name)s)"
-    + ");data_->setArgument(%(index)d,attr);}"
+    "set_value(%(index)d, (%(name)s));"
 )
 constructor_stmt_enum = (
-    "{IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();attr->set((IfcWrite::IfcWriteArgument::EnumerationReference(%(name)s,%(type)s::ToString(%(name)s)))"
-    + ");data_->setArgument(%(index)d,attr);}"
+    "set_value(%(index)d, (IfcWrite::IfcWriteArgument::EnumerationReference(%(name)s,%(type)s::ToString(%(name)s))));"
 )
 constructor_stmt_array = (
-    "{IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();attr->set((%(name)s)->generalize()"
-    + ");data_->setArgument(%(index)d,attr);}"
+    "set_value(%(index)d, (%(name)s)->generalize());"
 )
 constructor_stmt_derived = (
-    "{IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();attr->set(IfcWrite::IfcWriteArgument::Derived()"
-    + ");data_->setArgument(%(index)d,attr);}"
+    ""
+)
+constructor_stmt_instance = (
+    "set_value(%(index)d, %(name)s ? %(name)s->as<IfcUtil::IfcBaseClass>() : (IfcUtil::IfcBaseClass*) nullptr);"
 )
 
-constructor_stmt_optional = " if (%(name)s) {%(stmt)s } else { IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument(); attr->set(boost::blank()); data_->setArgument(%(index)d, attr); }"
+constructor_stmt_optional = " if (%(name)s) {%(stmt)s }"
 
 inverse_implementation = '    inverse_map[Type::%(type)s].insert(std::make_pair("%(name)s", std::make_pair(Type::%(related_type)s, %(index)d)));'
 
diff --git a/src/ifcparse/IfcBaseClass.h b/src/ifcparse/IfcBaseClass.h
index a68a86eeff..d75488a237 100644
--- a/src/ifcparse/IfcBaseClass.h
+++ b/src/ifcparse/IfcBaseClass.h
@@ -106,6 +106,11 @@ class IFC_PARSE_API IfcBaseClass : public virtual IfcBaseInterface {
 
     virtual const IfcParse::declaration& declaration() const = 0;
 
+    template <typename T>
+    void set_value(int index, const T& value);
+
+    void unset_value(int index);
+
     uint32_t identity() const { return identity_; }
 };
 
diff --git a/src/ifcparse/IfcParse.cpp b/src/ifcparse/IfcParse.cpp
index 125d2e2fd2..26c07f06ed 100644
--- a/src/ifcparse/IfcParse.cpp
+++ b/src/ifcparse/IfcParse.cpp
@@ -2712,3 +2712,32 @@ std::atomic_uint32_t IfcUtil::IfcBaseClass::counter_(0);
 
 bool IfcParse::IfcFile::lazy_load_ = true;
 bool IfcParse::IfcFile::guid_map_ = true;
+
+template <typename T>
+void IfcUtil::IfcBaseClass::set_value(int index, const T& value) {
+    IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();
+    attr->set(value);
+    data_->setArgument(index, attr);
+}
+
+void IfcUtil::IfcBaseClass::unset_value(int index) {
+    IfcWrite::IfcWriteArgument* attr = new IfcWrite::IfcWriteArgument();
+    data_->setArgument(index, attr);
+}
+
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<int>(int index, const int& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<bool>(int index, const bool& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<boost::logic::tribool>(int index, const boost::logic::tribool& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<double>(int index, const double& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<std::string>(int index, const std::string& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<boost::dynamic_bitset<>>(int index, const boost::dynamic_bitset<>& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<IfcWrite::IfcWriteArgument::EnumerationReference>(int index, const IfcWrite::IfcWriteArgument::EnumerationReference& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<IfcUtil::IfcBaseClass*>(int index, IfcUtil::IfcBaseClass* const& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<std::vector<int>>(int index, const std::vector<int>& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<std::vector<double>>(int index, const std::vector<double>& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<std::vector<std::string>>(int index, const std::vector<std::string>& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<std::vector<boost::dynamic_bitset<>>>(int index, const std::vector<boost::dynamic_bitset<>>& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<aggregate_of_instance::ptr>(int index, const aggregate_of_instance::ptr& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<std::vector<std::vector<int>>>(int index, const std::vector<std::vector<int>>& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<std::vector<std::vector<double>>>(int index, const std::vector<std::vector<double>>& value);
+template void IFC_PARSE_API IfcUtil::IfcBaseClass::set_value<aggregate_of_aggregate_of_instance::ptr>(int index, const aggregate_of_aggregate_of_instance::ptr& value);