List<T> newList = null;
        for (int i = 0; i < list.size(); i++) {
            T oldT = list.get(i);
            T newT = modifer.apply(oldT);
            if (newT != oldT) {
                if (newList == null) {
                    newList = new ArrayList<>(list);
                }
                newList.set(i, newT);
            }
        }
        return newList;

        List<T> newList = list;
        for (int i = 0; i < newList.size(); i++) {
            T oldT = newList.get(i);
            T newT = mapper.apply(oldT);
            if (newT != oldT) {
                if (newList == list) {
                    newList = new ArrayList<>(list);
                }
                newList.set(i, newT);
            }
        }
        return newList;