added MetadataMixIn, included in Tag

Author: asobolev

+nix/MetadataMixIn.m

@@ -0,0 +1,21 @@
+classdef MetadataMixIn < handle
+    %MetadataMixIn
+    % mixin class for nix entities with metadata
+    
+    properties(Hidden)
+        metadataCache
+    end;
+    
+    methods
+        function obj = MetadataMixIn()
+            obj.metadataCache = nix.CacheStruct();
+        end
+        
+        function metadata = open_metadata(obj)
+            [obj.metadataCache, metadata] = nix.Utils.fetchObj(obj.updatedAt, ...
+                'Tag::openMetadataSection', obj.nix_handle, obj.metadataCache, @nix.Section);
+        end;
+    end
+    
+end
+

+nix/Tag.m

@@ -1,18 +1,15 @@
-classdef Tag < nix.NamedEntity
+classdef Tag < nix.NamedEntity & nix.MetadataMixIn
     %Tag nix Tag object
 
     properties (Access = protected)
         % namespace reference for nix-mx functions
         alias = 'Tag'
     end
 
-    properties(Hidden)
-        metadataCache
-    end;
-
     methods
         function obj = Tag(h)
             [email protected](h);
+            [email protected]();
 
             % assign dynamic properties
             obj.add_dyn_attr('position', 'rw');
@@ -23,8 +20,6 @@
             obj.add_dyn_relation('references', @nix.DataArray);
             obj.add_dyn_relation('features', @nix.Feature);
             obj.add_dyn_relation('sources', @nix.Source);
-            
-            obj.metadataCache = nix.CacheStruct();
         end;
 
         % ------------------
@@ -94,14 +89,5 @@
                 'Tag::openSource', id_or_name, @nix.Source);
         end;
 
-        % ------------------
-        % Metadata methods
-        % ------------------
-
-        function metadata = open_metadata(obj)
-            [obj.metadataCache, metadata] = nix.Utils.fetchObj(obj.updatedAt, ...
-                'Tag::openMetadataSection', obj.nix_handle, obj.metadataCache, @nix.Section);
-        end;
-
     end;
 end