请改写下述代码片断并确保代码聚焦于Player类的方法定义，去掉了一些比较不重要的代码细节。如下：

```cpp 
class World {
    // ...
    std::vector<Player*> players;
    std::vector<Enemy*> enemies;
    void addPlayer(Player* player);
    void addEnemy(Enemy* enemy);
    void update();
    void render();
};

struct Position {
    float x;
    float y;
};

class Player {
    // ...
    Position position;
    void move(float dx, float dy);
    void update();
};
```
user
```cpp
class Player {
    Position position;
    void move(float dx, float dy);
    void update();
};
```
assistant