【Pybind11】：无法区别 const 和非 const 成员函数

  /**
   * @brief Get value in Loss with key.
   *
   * @return const std::map<std::string, LossCurve> & value in Loss at key.
   * @warning The key must be exist in Loss. otherwise, the behavior is undefined and will cause segmentation fault.
   */
  NO_DISCARD const LossCurve & get_loss(const std::string &key) const;

  /**
   * @brief Get mutable reference of value in Loss with key.
   * A new key and default value will be created if the key does not exist.
   *
   * @return LossCurve& the mutable reference of value in Loss at key.
   */
  LossCurve &get_loss(const std::string &key);

• 目前实现中，会被重复绑定。尚不清楚具体的表现。