class move_only {
  std::unique_ptr<my_class> data;

public:
  move_only(const move_only&) = delete;
  move_only(move_only&& other) : data(std::move(other.data)) {}
  move_only& operator=(const move_only&) = delete;
  move_only& operator                    =(move_only&& other)
  {
    data = std::move(other.data);
    return *this;
  }
};
move_only m1;
move_only m2(m1);
move_only m3(std::move(m1));