[Boost-users] [serialization] postprocessing object after deserialization

Subject: [Boost-users] [serialization] postprocessing object after deserialization
From: Václav Šmilauer (eudoxos_at_[hidden])
Date: 2010-04-19 06:03:04

Hi, I am using boost::serialization for hierarchy of classes; I need to
process attributes after deserialization, but I am facing some (perhaps
design) issues. The top class is Serializable, with serialization code
like this:

struct Serializable{
        friend class boost::serialization::access;
        virtual void preProcess(bool deserializing){}
        virtual void postProcess(bool deserializing){}
        template <class ArchiveT>
        void serialize(ArchiveT & ar, unsigned int version){
                                                            // this sequence is always the same:
                preProcess(ArchiveT::is_loading::value);    // preprocess
                 /* no base class to be serialized */        // serialize base class
                 /* no attributes in Serializable itself */  // serialize attributes
                postProcess(ArchiveT::is_loading::value);   // postprocess
        };
};

Each derived class then defines serialize function and optionally
overrides {pre,post}Process, which are meant for pre-computing some
non-serialized data from known attributes, for instance.

struct Derived: public Serializable{
        friend class boost::serialization::access;
        template <class ArchiveT>
        void serialize(ArchiveT & ar, unsigned int version){
                preProcess(ArchiveT::is_loading::value);    // preprocess
                ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(Serializable);  // base class
                ar & BOOST_SERIALIZATION_NVP(attr1);        // attributes
                ar & BOOST_SERIALIZATION_NVP(attr2);
                postProcess(ArchiveT::is_loading::value);   // postprocess
        }
};

The problem is that {pre,post}Process are not overridden in most cases
and will be called multiple times, perhaps with invalid data:

e.g. when deserializing derived class, postProcess will be called for
each parent class; since it is virtual, it will end up calling
Derived::postProcess _before_ attr1 and attr2 are deserialized from
archive. Later, it will be called again.

My questions are therefore:

1. If boost::serialization provides some hook functions for this purpose
(I didn't find anything in documentation and via google either)

2. If you can suggest some way to have the {pre,post}Process function
called for each class exactly once, at the right place(s).

Best regards, Vaclav