Robert Ramey wrote:
OK - A2 produces an archive that cannot be read. I would argue that including the dummy just to provoke this "bug" is just a pathological case and basically constitutes an error - albiet a subtle one.
A much more interesting scenario in this vein is the following:
C: Sometime later, the definition of X is changed to
struct X { vector<char> * m_pv; template<class Archive> save(Archive & ar, const unsigned int version) const { ar << m_pv; } template<class Archive> load(Archive & ar, const unisgned int version){ // uh - oh need to support old archives ! if(version < 1){ m_pv = new vector<char>() ar >> *m_pv } else ar >> m_pv; } };
BOOST_CLASS_VERSION(X, 1)
This WOULD be a problem and would fail to read old archives. I'm willing to consider this a legitimate concern.
Still, it's a very infrequent cases.
So in short, I believe that the only way to have such a problem is include dummy code which I don't consider a huge problem.
Both cases alltought maybe not a most common are nevertheless legitimate. We use extensively serialization framework in our code and case when someone changes a class data member to be handled with a shared pointer would not surprise me at all. However the user would be unaware of the subtility of a such change and a fact that would make old archives unreadable. Similar situation would be I beleive adding shared_from_this<T> as a base class - no versioning could help restore the old archives...