Value traverse to Struct parent

src/data.cpp

@@ -373,11 +373,29 @@ void Value::traverse(const std::string &expr, bool modify)
 {
     size_t pos=0;
     while(desc && pos<expr.size()) {
+        if(expr[pos]=='<') {
+            // attempt traverse to parent
+            if(desc!=store->top->desc.get())
+            {
+                auto pdesc = desc - desc->parent_index;
+                std::shared_ptr<FieldStorage> pstore(store, store.get() - desc->offset + pdesc->offset);
+                store = std::move(pstore);
+                desc = pdesc;
+                pos++;
+                continue;
+            } else {
+                // at top
+                store.reset();
+                desc = nullptr;
+                break;
+            }
+
+        }
 
         if(desc->code.code==TypeCode::Struct) {
             // attempt traverse to member.
             // expect: [0-9a-zA-Z_.]+[\[-$]
-            size_t sep = expr.find_first_of("[-", pos);
+            size_t sep = expr.find_first_of("<[-", pos);
 
             decltype (desc->mlookup)::const_iterator it;
 
@@ -409,7 +427,7 @@ void Value::traverse(const std::string &expr, bool modify)
 
                 } else {
                     // select member of Union
-                    size_t sep = expr.find_first_of("[-.", pos);
+                    size_t sep = expr.find_first_of("<[-.", pos);
 
                     decltype (desc->mlookup)::const_iterator it;
 

src/dataencode.cpp

@@ -163,6 +163,7 @@ void from_wire(Buffer& buf, TypeDeserContext& ctxt, unsigned depth)
                 // descs may be re-allocated (invalidating previous refs.)
                 auto& fld = ctxt.descs[index];
                 auto& cfld = ctxt.descs[cindex];
+                cfld.parent_index = cindex-index;
 
                 // update hash
                 // TODO investigate better ways to combine hashes

src/dataimpl.h

@@ -69,6 +69,10 @@ struct FieldDesc {
     // number of FieldDesc nodes which describe this node and decendents.  Inclusive.  always >=1
     // eg. num_index+(FieldDesc*)this jumps to next sibling
     size_t num_index=0;
+    // number of FieldDesc nodes between this node and it's a parent node (if any).
+    // This value also appears in the parent's miter and mlookup mappings.
+    // Only usable when a StructTop is accessible and this!=StructTop::desc
+    size_t parent_index=0;
     TypeCode code{TypeCode::Null};
 
     // number of FieldDesc nodes which describe this node.  Inclusive.  always size()>=1

src/type.cpp

@@ -196,6 +196,7 @@ void build_tree(std::vector<FieldDesc>& desc, const Member& node)
 
         auto& fld = desc[index];
         auto& child = desc[cindex];
+        child.parent_index = cindex-index;
 
         fld.hash ^= std::hash<std::string>{}(cnode.name) ^ child.hash;
 
@@ -319,8 +320,7 @@ void FieldDesc_calculate_offset(FieldDesc* const top)
 {
     top->offset = 0;
     uint16_t offset = 1;
-    size_t index = 1;
-    while(index < top->size()) {
+    for(size_t index = 1; index < top->size(); ) {
         auto& fld = top[index];
 
         switch (fld.code.code) {

test/testdata.cpp

@@ -342,15 +342,35 @@ void testDeserialize2()
     }
 }
 
+void testTraverse()
+{
+    auto top = nt::NTScalar{TypeCode::Int32, true}.create();
+
+    testOk1(!top["<"].valid());
+
+    {
+        auto top2 = top["value<"];
+        testOk1(top.compareType(top2));
+        testOk1(top.compareInst(top2));
+    }
+    {
+        auto sevr1 = top["alarm.severity"];
+        auto sevr2 = top["value<alarm.status<severity"];
+        testOk1(sevr1.compareType(sevr2));
+        testOk1(sevr1.compareInst(sevr2));
+    }
+}
+
 } // namespace
 
 MAIN(testdata)
 {
-    testPlan(58);
+    testPlan(63);
     testSerialize1();
     testDeserialize1();
     testSerialize2();
     testDeserialize2();
+    testTraverse();
     cleanup_for_valgrind();
     return testDone();
 }