// returns number of changes
static int cset_compareByStruct(Concept c, O... values) ctex {
  int changes = 0;
  values = expandParams(c.getClass(), values);
  warnIfOddCount(values);
  for (int i = 0; i+1 < l(values); i += 2) {
    S field = (S) values[i];
    O value = values[i+1];
    Field f = setOpt_findField(c.getClass(), field);
    //print("cset: " + c.id + " " + field + " " + struct(value) + " " + f);
    if (value instanceof RC) value = c._concepts.getConcept((RC) value);
    value = deref(value);
    
    if (value instanceof S && l((S) value) >= concepts_internStringsLongerThan) value = intern((S) value);
    
    if (f == null) {
      // TODO: keep ref if it exists
      mapPut2(c.fieldValues, field, value instanceof Concept ? c.new Ref((Concept) value) : value);
      c.change();
    } else if (isSubtypeOf(f.getType(), Concept.Ref.class)) {
      ((Concept.Ref) f.get(c)).set((Concept) derefRef(value));
      c.change(); ++changes;
    } else {
      O old = f.get(c);
      if (!structEq(value, old)) {
        f.set(c, value);
        if ((f.getModifiers() & java.lang.reflect.Modifier.TRANSIENT) == 0) c.change(); 
        ++changes;
      }
    }
  }
  ret changes;
}