CharListenKnoten* MyString2::deep_copy() const {
    if (!m_anker)
        return nullptr;
    CharListenKnoten* new_ptr   = new CharListenKnoten(m_anker->get_data());
    CharListenKnoten* new_anker = new_ptr;
    CharListenKnoten* ptr       = m_anker;
    while (ptr->get_next()) {
        ptr = ptr->get_next();
        new_ptr->set_next(new CharListenKnoten(ptr->get_data()));
        new_ptr = new_ptr->get_next();
    }
    return new_anker;
}