diff --git a/src/codegen.inc.php b/src/codegen.inc.php
index 1c1e495..441f567 100644
--- a/src/codegen.inc.php
+++ b/src/codegen.inc.php
@@ -86,6 +86,16 @@ function _add_twig_support(\Twig\Environment $twig)
       return \mtg_get_all_fields($meta, $o);
     }
   ));
+  $twig->addFunction(new \Twig\TwigFunction('count_optional', 
+    function($units) 
+    {
+      $opts = 0;
+      foreach($units as $u)
+        if($u->hasToken('optional'))
+          ++$opts;
+      return $opts;
+    }
+  ));
   $twig->addFilter(new \Twig\TwigFilter('go_type', 
     function($type, $tokens) 
     {
diff --git a/tpl/macro.twig b/tpl/macro.twig
index ce3c784..9a23fc7 100644
--- a/tpl/macro.twig
+++ b/tpl/macro.twig
@@ -11,6 +11,12 @@
 {% endmacro %}
 
 {% macro decl_struct(meta, o) %}
+{%- if o.parent and has_token(o, 'POD') -%}
+{{Error("@POD structs can't have a parent: " ~ o.name)}}
+{%- endif -%}
+{%- if o.parent and has_token(o, 'bitfields') -%}
+{{Error("@bitfields structs can't have a parent: " ~ o.name)}}
+{%- endif ~%}
 
 //==============================
 type {{o.name}} struct {
@@ -33,7 +39,7 @@ type I{{o.name}} interface {
   Ptr{{o.name}}() *{{o.name}}
 }
 func (*{{o.name}}) CLASS_ID() uint32 {
-  return %class_id%
+  return {{o.classid}}
 }
 func (*{{o.name}}) CLASS_NAME() string {
   return "{{o.name}}"
@@ -71,7 +77,9 @@ func (self *{{o.name}}) Read(reader meta.Reader) error {
 }
 func (self *{{o.name}}) ReadFields(reader meta.Reader) error {
   self.Reset()
-  %read_buffer%
+
+  {{_self.struct_read_fields(o)}}
+
   return nil
 }
 func (self *{{o.name}}) Write(writer meta.Writer) error {
@@ -121,6 +129,31 @@ fieldsMask meta.FieldsMask //@bitfields support
 
 {% endmacro %}
 
+{% macro struct_read_fields(o) %}
+
+{%if has_token(o, 'bitfields') %}
+  use_mask, mask, err := reader.TryReadMask()
+  if err != nil {
+   return err
+  }
+  self.fieldsMask = mask
+{%- endif ~%}
+
+  _cont_size, err := reader.GetContainerSize()
+  if err != nil {
+    return err
+  }
+
+  if _cont_size < {{o.fields|length - count_optional(o.fields)}} {
+    _cont_size = {{o.fields|length - count_optional(o.fields)}}
+  }
+
+{%- if o.parent ~%}
+  if err := self.{{o.parent.name}}.ReadFields(reader); err != nil { return err }
+{%- endif -%}
+
+{% endmacro %}
+
 {% macro decl_enum(o) %}
 
 //==============================