@Override
        public Type visitClassType(ClassType t, Void s) {
            ListBuffer<Type> rewritten = new ListBuffer<Type>();
            boolean changed = false;
            for (Type arg : t.allparams()) {
                Type bound = visit(arg);
                if (arg != bound) {
                    changed = true;
                }
                rewritten.append(bound);
            }
            if (changed)
                return subst(t.tsym.type,
                        t.tsym.type.allparams(),
                        rewritten.toList());
            else
                return t;
        }