STYLE: use HashSet xor instead of two operations (faceZoneSet)

STYLE: use global operator instead of HashSet -= operator

applications/utilities/mesh/manipulation/checkMesh/checkMesh.C

@@ -166,8 +166,7 @@ int main(int argc, char *argv[])
     if (args.found("writeFields"))
     {
         selectedFields = args.getList<word>("writeFields");
-        wordHashSet badFields(selectedFields);
-        badFields -= allFields;
+        const wordHashSet badFields(selectedFields - allFields);
 
         if (!badFields.empty())
         {
@@ -229,7 +228,7 @@ int main(int argc, char *argv[])
                     IOobject::MUST_READ,
                     IOobject::NO_WRITE
                 )
-           )
+            )
         );
     }
 

src/meshTools/sets/topoSets/faceZoneSet.C

@@ -320,17 +320,11 @@ void Foam::faceZoneSet::sync(const polyMesh& mesh)
     {
         const labelHashSet zoneSet(addressing_);
 
-        // Get elements that are in zone but not faceSet
-        labelHashSet badSet(zoneSet);
-        badSet -= *this;
+        // Elements that are in zone but not faceSet, and
+        // elements that are in faceSet but not in zone
+        labelHashSet badSet(*this ^ zoneSet);
 
-        // Add elements that are in faceSet but not in zone
-        labelHashSet fSet(*this);
-        fSet -= zoneSet;
-
-        badSet += fSet;
-
-        label nBad = returnReduce(badSet.size(), sumOp<label>());
+        const label nBad = returnReduce(badSet.size(), sumOp<label>());
 
         if (nBad)
         {