Method ~optional

include/dmlc/optional.h:70–74

! \brief deconstructor */

  }
  /*! \brief deconstructor */
  ~optional() {
    if (!is_none) {
      reinterpret_cast<T*>(&val)->~T();
    }
  }
  /*! \brief swap two optional */
  void swap(optional<T>& other) {
    std::swap(val, other.val);