Re: [Boost-users] Question about versioning of serialization

From: Robert Ramey (ramey_at_[hidden])
Date: 2007-10-19 11:53:04

I've never thought about this, but my first attempt would be something like  the following:

template<class Archive>
void load(Archiv &ar , C &c, const unsigned int version){
    if(version < 4>)
        ar >> boost::serialization::base_object<A>(c);
    else
        ar >> boost::serialization::base_object<B>(c);
}
  "Fred Lupien" <fred.lupien_at_[hidden]> wrote in message news:32e6d6bf0710190708x45191057ld2a23a92399f59e4_at_mail.gmail.com...
  Hello,

        we are currently implementing serialization versioning using boost and I am curious to know if their is a way to support a changing class hierarchy. Let's say C derives from A for a while and then a change requires C to derive from B instead, which derives from A. Is it possible to support such a change provided we know what default values are needed for the new class? I tried and even if don't serialize anything in class C I get stream errors because I believe boost saves some base info for each class. When it tries to reload those value from a old stream, obviously it desynchronizes it because the values are not in the stream. So is their a way around this? 

  Also is it possible to support the removal of a class. If, for exemple C derives from B which in turn derives from A and suddenly B is removed. Is their a way to deal with this without invalidating all previously saved data? 

  *** I doubt it.  If you want to load old archives, you have know how much to "skip" over.  The only thing that MIGHT be possible
  is something like:
  template<class Archive>
  void load(Archiv &ar , C &c, const unsigned int version){
      if(version < 4>){
          class a; //no longer used
          ar >> a;
          // throw away old data on leaving scope
      }
      else
          ar >> boost::serialization::base_object<B>(c);
  }

  Thank you for your help!

  -- 
  Frédérick Martel-Lupien
  Étudiant en Génie Informatique
  Université de Sherbrooke
  fred.lupien_at_[hidden] 

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