diff --git a/src/dataencode.cpp b/src/dataencode.cpp
index 811eb67..ec10bc8 100644
--- a/src/dataencode.cpp
+++ b/src/dataencode.cpp
@@ -90,12 +90,7 @@ void from_wire(Buffer& buf, std::vector<FieldDesc>& descs, TypeStore& cache, uns
             return;
 
         } else {
-            auto& entry = cache[key];
-            // copy new node, and any descendants into cache
-            entry.resize(descs.size()-index);
-            std::copy(descs.begin()+index,
-                      descs.end(),
-                      entry.begin());
+            cache.emplace(key, descs); // copies descs
 
             descs[index].parent_index = 0u; // our caller will set if actually is a parent.
         }
@@ -115,10 +110,9 @@ void from_wire(Buffer& buf, std::vector<FieldDesc>& descs, TypeStore& cache, uns
 
         } else {
             // copy from cache
-            descs.resize(index+it->second.size());
-            std::copy(it->second.begin(),
-                      it->second.end(),
-                      descs.begin()+index);
+            descs.reserve(index+it->second.size());
+            for(const auto& d : it->second)
+                descs.emplace_back(d);
         }
 
     } else if(code.code!=0xff && code.code&0x10) {
@@ -128,12 +122,7 @@ void from_wire(Buffer& buf, std::vector<FieldDesc>& descs, TypeStore& cache, uns
     } else {
         // actual field
 
-        descs.emplace_back();
-        {
-            auto& fld = descs.back();
-
-            fld.code = code;
-        }
+        descs.emplace_back(code);
 
         switch(code.code) {
         case TypeCode::StructA:
diff --git a/src/dataimpl.h b/src/dataimpl.h
index cbbca86..cc7c93b 100644
--- a/src/dataimpl.h
+++ b/src/dataimpl.h
@@ -74,7 +74,9 @@ struct FieldDesc {
     // For UnionA/StructA containing a single Union/Struct
     std::vector<FieldDesc> members;
 
-    TypeCode code{TypeCode::Null};
+    const TypeCode code{TypeCode::Null};
+
+    explicit FieldDesc(TypeCode code) :code{code} {}
 
     // number of FieldDesc nodes which describe this node.  Inclusive.  always size()>=1
     inline size_t size() const { return 1u + (members.empty() ? mlookup.size() : 0u); }
diff --git a/src/type.cpp b/src/type.cpp
index a316ed7..46d2282 100644
--- a/src/type.cpp
+++ b/src/type.cpp
@@ -235,9 +235,7 @@ void Member::Helper::build_tree(std::vector<FieldDesc>& desc, const Member& node
     auto code = node.code;
     if(node.code==TypeCode::StructA || node.code==TypeCode::UnionA) {
 
-        desc.emplace_back();
-        auto& fld = desc.back();
-        fld.code = node.code;
+        desc.emplace_back(node.code);
         // struct/union array have no ID
 
         Member next{code.scalarOf(), node.name};
@@ -249,11 +247,10 @@ void Member::Helper::build_tree(std::vector<FieldDesc>& desc, const Member& node
     }
 
     const auto index = desc.size();
-    desc.emplace_back();
+    desc.emplace_back(code);
 
     {
         auto& fld = desc.back();
-        fld.code = code;
         fld.id = node.id;
     }