Re: [boost] [fileststem]1.32: with serilization: visibility of m_path

From: Beman Dawes (bdawes_at_[hidden])
Date: 2004-11-08 11:07:16

At 04:13 AM 11/8/2004, Francis ANDRE wrote:
 >Hi
 >
 >In order to serialize a  derivative class of boost/filesystem/path, one
 >cannot access the base class member  m_path without  changing its
 >visibility
 >from private to protected:
 >
 >I would suggest to change the visibility of this m_path member from
 >private: to protected, or to add an implicit definition of the serialize
 >method into the class boost::filesystem::path.
 >
 >#include <boost/filesystem/path.hpp>
 >namespace boost { namespace serialization { class access; }}
 >
 >class OSD : public boost::filesystem::path {
 >private:
 >        friend class boost::serialization::access;
 >        friend std::ostream & operator<<(std::ostream &os, const OSD&);
 >        template<class Archive>
 >        void serialize(Archive &ar, const unsigned int version) {
 >            ar & m_path;
 >        }
 >};

I don't particularly like either of those solutions.

* Changing m_path from private to protected effectively adds m_path to the 
class interface, yet m_path is an implementation artifact that might not be 
present at all in a different implementation.

* Adding a dependency to the serialization library isn't a good idea 
either. No matter how nice boost.serialization is, some boost.filesystem 
users will not wish to use it, and will not want the dependency.

Class path already has a member, path::string(), which in the current 
implementation returns a reference to m_path, and in any implementation 
must return the equivalent of a const reference to m_path. Going the other 
way, the append function can be used to import a serialized string. I'm not 
familiar with how boost.serialization works, but wouldn't you be better off 
to use those already public functions for serialization?

If not, I'm willing to make m_path protected, but would like to explore 
other approaches to the serialization problem first.

Thanks,

--Beman