Added visit_layers_until_tag()

dlib/dnn/core.h

@@ -3475,6 +3475,71 @@ namespace dlib
         impl::vl_loop_backwards<begin,end>::visit(net, v);
     }
 
+// ----------------------------------------------------------------------------------------
+
+    namespace impl
+    {
+        template <size_t i, unsigned long tag_id>
+        struct vl_until_tag
+        {
+            template <
+                typename net_type,
+                typename next_net_type,
+                typename visitor
+                >
+            static void visit(
+                net_type& net,
+                next_net_type& next_net,
+                visitor&& v
+            )
+            {
+                v(next_net);
+                vl_until_tag<i+1,tag_id>::visit(net,layer<i+1>(net),v);
+            }
+
+            template <
+                typename net_type,
+                typename SUBNET,
+                typename visitor
+                >
+            static void visit(
+                net_type& net,
+                const add_tag_layer<tag_id,SUBNET>& next_net,
+                visitor&& v
+            )
+            {
+                v(next_net);
+            }
+
+            template <
+                typename net_type,
+                typename SUBNET,
+                typename visitor
+                >
+            static void visit(
+                net_type& net,
+                add_tag_layer<tag_id,SUBNET>& next_net,
+                visitor&& v
+            )
+            {
+                v(next_net);
+            }
+        };
+    }
+
+    template <
+        unsigned long tag_id,
+        typename net_type,
+        typename visitor
+        >
+    void visit_layers_until_tag(
+        net_type& net,
+        visitor v
+    )
+    {
+        impl::vl_until_tag<0,tag_id>::visit(net, net, v);
+    }
+
 // ----------------------------------------------------------------------------------------
 
 }

dlib/dnn/core_abstract.h

@@ -1578,6 +1578,38 @@ namespace dlib
                     v(i-1, layer<i-1>(net));
     !*/
 
+// ----------------------------------------------------------------------------------------
+
+    template <
+        unsigned long tag_id,
+        typename net_type,
+        typename visitor
+        >
+    void visit_layers_until_tag(
+        net_type& net,
+        visitor v
+    );
+    /*!
+        requires
+            - net_type is an object of type add_layer, add_loss_layer, add_skip_layer, or
+              add_tag_layer.
+            - v is a function object with a signature equivalent to: 
+                v(any_net_type& t)
+              That is, it must take any of the network types such as add_layer,
+              add_loss_layer, etc.
+        ensures
+            - Loops over all the layers in net beginning with layer<0>(net) and going until
+              a tag layer with an ID of tag_id is encountered.  To be specific, this
+              function essentially performs the following:
+
+                size_t i = 0;
+                while(layer<i>(net) isn't an add_tag_layer with ID == tag_id) {
+                    v(layer<i>(net));
+                    ++i;
+                }
+                v(layer<i>(net));  // also visits the tag layer itself at the very end.
+    !*/
+
 // ----------------------------------------------------------------------------------------
 
     struct layer_test_results