diff --git a/src/codegen.inc.php b/src/codegen.inc.php
index 683f9bd..787eb2d 100644
--- a/src/codegen.inc.php
+++ b/src/codegen.inc.php
@@ -122,6 +122,12 @@ function _add_twig_support(\Twig\Environment $twig)
       return is_primary_field($o, $f);
     }
   ));
+  $twig->addFunction(new \Twig\TwigFunction('get_diff_class_units', 
+    function($meta, $o) 
+    { 
+      return get_diff_class_units($meta, $o);
+    }
+  ));
 }
 
 function cs_type(\mtgType $type)
@@ -434,3 +440,7 @@ function is_nullable_type(\mtgType $type)
          ($type instanceof \mtgMetaStruct && !$type->hasToken('POD'));
 }
 
+function get_diff_class_units(\mtgMetaInfo $meta, \mtgMetaStruct $struct)
+{
+  return [];
+}
diff --git a/tpl/codegen_bundle.twig b/tpl/codegen_bundle.twig
index 34082e4..4a4e8b8 100644
--- a/tpl/codegen_bundle.twig
+++ b/tpl/codegen_bundle.twig
@@ -4,9 +4,9 @@ using metagen;
 
 {%- import "macro.twig" as macro -%}
 
-{#{% if namespace is defined ~%}
+{% if namespace is defined ~%}
 namespace {{namespace}} {
-{% endif %}#}
+{% endif %}
 
 {{ macro.decl_units(meta) }}
 
@@ -61,6 +61,6 @@ static public class AutogenBundle
   }
 }
 
-{#{% if namespace is defined ~%}
+{% if namespace is defined ~%}
 } //namespace {{namespace}}
-{% endif %}#}
+{% endif %}
diff --git a/tpl/macro.twig b/tpl/macro.twig
index 28febb4..a02256a 100644
--- a/tpl/macro.twig
+++ b/tpl/macro.twig
@@ -3,17 +3,17 @@
 
 {%- for u in meta.getunits ~%}
 {%- if u.object is instanceof('\\mtgMetaStruct') -%}
-{{ _self.decl_struct(u.object) }}
+{{ _self.decl_struct(meta, u.object) }}
 {%- elseif u.object is instanceof('\\mtgMetaEnum') -%}
 {{ _self.decl_enum(u.object) }}
 {%- elseif u.object is instanceof('\\mtgMetaRPC') -%}
-{{ _self.decl_rpc(u.object) }}
+{{ _self.decl_rpc(meta, u.object) }}
 {%- endif ~%}
 {%- endfor ~%}
 
 {% endmacro %}
 
-{% macro decl_struct(o, extra = '') %}
+{% macro decl_struct(meta, o, extra = '') %}
 {%- if o.parent and has_token(o, 'POD') -%}
 {{Error("@POD structs can't have a parent: " ~ o.name)}}
 {%- endif -%}
@@ -100,6 +100,17 @@ public {{_self.struct_type(o)}} {{o.name}} {{_self.base_struct_class(o)}}
   {{_self.get_itype(o)}}
 {%- endif -%}
   
+{%- if has_token(o, 'id') ~%}
+  public ulong getPrimaryId() 
+  {
+    return (ulong){{token(o, 'id')}};
+  }
+{%- endif -%}
+
+{%- if has_token(o, 'diffable') ~%}
+  {{_self.diffable_support(meta, o)}}
+{%- endif -%}
+
   {{extra}}
 }
 
@@ -282,10 +293,10 @@ public enum {{o.name}}
 }
 {% endmacro %}
 
-{% macro decl_rpc(o) %}
+{% macro decl_rpc(meta, o) %}
 
-{{_self.decl_struct(o.req)}}
-{{_self.decl_struct(o.rsp)}}
+{{_self.decl_struct(meta, o.req)}}
+{{_self.decl_struct(meta, o.rsp)}}
 
 public class {{o.name}} : IRpc
 {
@@ -320,3 +331,154 @@ public class {{o.name}} : IRpc
 }
 
 {% endmacro %}
+
+{%- macro diffable_support(meta, o) -%}
+
+    {% for u in get_diff_class_units(meta, o) %}
+    {{_self.diff_methods(u)}}
+    {% endfor %}
+
+    static public List<ulong> GetClassRemovedIds(List<DataClassIds> removed_ids, uint class_id) 
+    {
+      if(removed_ids == null)
+        return null;
+      DataClassIds res;
+      if(!FindClassRemovedIds(removed_ids, class_id, out res))
+      {
+        res = new DataClassIds();
+        res.class_id = class_id;
+        res.ids = new List<ulong>();
+        removed_ids.Add(res);
+      }
+      return res.ids;
+    }
+
+    static bool FindClassRemovedIds(List<DataClassIds> removed_ids, uint class_id, out DataClassIds res)
+    {
+      for(int i=0;i<removed_ids.Count;++i)
+      {
+        if(removed_ids[i].class_id == class_id)
+        {
+          res = removed_ids[i];
+          return true;
+        }
+      }
+      res = default(DataClassIds);
+      return false;
+    }
+
+{% endmacro %}
+
+{%- macro diff_methods(u) -%}
+
+  static public bool DiffOne(ref {{u.name}} curr, {{u.name}} old)
+  {
+    return !{{_self.compare_func_name(u)}}(ref curr, old);
+  }
+
+  static public bool DiffCollection(List<{{u.name}}> items, List<{{u.name}}> old_items, List<{{u.name}}> changed, List<DataClassIds> removed)
+  {
+    bool has_diff = false;
+    if(changed != null)
+      changed.Clear();
+
+    SortByPrimaryId(ref items);
+    SortByPrimaryId(ref old_items);
+
+    int i = 0;
+    int old_i = 0;
+    for(; i < items.Count && old_i < old_items.Count;)
+    {
+      var old = old_items[old_i];
+      var item = items[i];
+
+      if(old.getPrimaryId() < item.getPrimaryId())
+      {
+        var removed_ids = GetClassRemovedIds(removed, {{u.name}}.STATIC_CLASS_ID);
+        if(removed_ids != null)
+          removed_ids.Add(old.getPrimaryId());
+        old_i++;
+        has_diff = true;
+      }
+      else if(old.getPrimaryId() > item.getPrimaryId())
+      {
+        item.SetDirtyMask();
+        if(changed != null)
+          changed.Add(item);
+        i++;
+        has_diff = true;
+      }
+      else
+      {
+        if(!{{_self.compare_func_name(u)}}(ref item, old))
+        {
+          if(changed != null)
+            changed.Add(item);
+          has_diff = true;
+        }
+
+        i++;
+        old_i++;
+      }
+    }
+
+    //items leftovers are considered changed
+    for(; i < items.Count; i++)
+    {
+      var item = items[i];
+      item.SetDirtyMask();
+      if(changed != null)
+        changed.Add(item);
+      has_diff = true;
+    }
+
+    //old items leftovers are considered removed
+    for(; old_i < old_items.Count; old_i++)
+    {
+      var removed_ids = GetClassRemovedIds(removed, {{u.name}}.STATIC_CLASS_ID);
+      if(removed_ids != null)
+        removed_ids.Add(old_items[old_i].getPrimaryId());
+      has_diff = true;
+    }
+
+    //if(changed.Count > 0)
+    //  Meta.LogDebug("Changed in collection {{u.name}}");
+    //if(removed_ids.Count > 0)
+    //  Meta.LogDebug("Removed in collection {{u.name}}");
+
+    return has_diff;
+  }
+
+  class {{u.name}}Compare : IComparer<{{u.name}}>
+  {
+    public int Compare({{u.name}} o1, {{u.name}} o2)
+    { 
+      var id1 = o1.getPrimaryId();
+      var id2 = o2.getPrimaryId();
+      if(id1 == id2)
+        return 0;
+      return id1 > id2 ? 1 : -1;
+    }
+  }
+
+  static {{u.name}}Compare {{u.name}}_compare = new {{u.name}}Compare();
+
+  static void SortByPrimaryId(ref List<{{u.name}}> list)
+  {
+    list.Sort({{u.name}}_compare); 
+  }
+
+  public static bool {{_self.compare_func_name(u)}}(ref {{u.name}} a, {{u.name}} b)
+  {
+    bool is_equal = true;
+
+    $compare_fn_str
+
+    return is_equal;
+  }
+
+{% endmacro %}
+
+{% macro compare_func_name(o) %}
+{{has_token(u, 'bitfields')?'CompareAndMarkFields':'IsEqual'}}
+{% endmacro %}