Tcl Source Code

Although the emphasis was "only once" referenced, but it is not always the case: the object newValue can be referenced twice or more (newValue->refCount > 1) and described situation can nevertheless still occur, if we've something like this:
<code><pre>
set X [list [list 1st-list $newValue] [list 2nd-list $newValue] ...]
call-something-that-set-var ::missing::namespace::var [call-something-unset-X-and-return-its-value X]
</pre></code>
I think this example describes the issue very good.

Thus my proposal to solve it (resp. to workaround it) using:
<pre><code>
<b style="color:green">+     int freeNewVal = (newValuePtr->refCount == 0);</b>

     part1 = TclGetString(part1Ptr);
     part2 = ((part2Ptr == NULL) ? NULL : TclGetString(part2Ptr));
  
     varPtr = TclObjLookupVar(interp, part1Ptr, part2, flags, "set",
            /*createPart1*/ 1, /*createPart2*/ 1, &arrayPtr);
     if (varPtr == NULL) {
<b style="color:red">-        if (newValuePtr->refCount == 0) {</b>
<b style="color:green">+        if (freeNewVal) {</b>
             Tcl_DecrRefCount(newValuePtr);
         }
         return NULL;
     }
</code></pre>