get the first diff verb to work

surprise surprise, no catastrophe thus far....

src/lib/diff/gen-node.hpp

@@ -692,7 +692,7 @@ namespace diff{
   
   /**
    * @return either the contents of a nested record's type field
-   *         or the Rec::TYPE_NIL marker.
+   *         or the util::BOTTOM_INDICATOR, when not a record.
    * @remarks this function never raises an error, even if the element
    *         in fact doesn't constitute a nested scope. Effectively this
    *         allows to "peek" into the contents to some degree.
@@ -709,7 +709,7 @@ namespace diff{
         }
       
       return nested? nested->getType()
-                   : Rec::TYPE_NIL;
+                   : util::BOTTOM_INDICATOR;
     }
   
   

src/lib/diff/test-mutation-target.hpp

@@ -133,18 +133,13 @@ namespace diff{
     inline string
     render (DataCap const& content)
     {
-      class StringRenderer
-        : public string
-        , public Variant<DataValues>::Visitor
+      struct StringRenderer
+        : public Variant<DataValues>::Visitor
         {
-          void
-          renderAs (string const& representation)
-            {
-              string::operator= (representation);
-            }
+          string representation{""};
           
 #define STRINGIFY_CONTENT(_TY_) \
-          virtual void handle  (_TY_& val) override { renderAs (util::toString (val)); }
+          virtual void handle  (_TY_& val) override { representation = util::toString (val); }
           
           STRINGIFY_CONTENT (int)
           STRINGIFY_CONTENT (int64_t)
@@ -164,22 +159,22 @@ namespace diff{
           virtual void
           handle  (Rec & rec) override
             {
-              renderAs (renderRecord (rec));
+              representation = renderRecord (rec);
             }
           
           virtual void
           handle  (RecRef & ref) override
             {
               if (ref)
-                renderAs (renderRecord (ref));
+                representation = renderRecord (ref);
               else
-                renderAs (util::BOTTOM_INDICATOR);
+                representation = util::BOTTOM_INDICATOR;
             }
         };
       
       StringRenderer visitor;
       unConst(content).accept (visitor);
-      return string(visitor);
+      return visitor.representation;
     }
     
   }//(End)diagnostic helpers

tests/library/diff/diff-virtualised-application-test.cpp

@@ -46,6 +46,7 @@ using std::make_unique;
 using std::string;
 using std::vector;
 using lib::time::Time;
+using util::BOTTOM_INDICATOR;
 
 
 namespace lib {
@@ -166,6 +167,10 @@ namespace test{
                           {
                             return not spec.isNamed();                // »Selector« : accept anything unnamed value-like
                           })
+                       .constructFrom ([&](GenNode const& spec) -> string
+                          {
+                            return string(spec);
+                          })
                        .assignElement ([&](string& target, GenNode const& spec) -> bool
                           {
                             target = render(spec.data);
@@ -174,7 +179,7 @@ namespace test{
                 .attach (collection(nestedObj_)
                        .isApplicableIf ([&](GenNode const& spec) -> bool
                           {
-                            return type_ == spec.data.recordType();    // »Selector« : require object-like sub scope with matching typeID
+                            return BOTTOM_INDICATOR != spec.data.recordType(); // »Selector« : require object-like sub scope
                           })
                        .constructFrom ([&](GenNode const& spec) -> Opaque
                           {