Joel de Guzman wrote:
Hi,
Here's a use case that I can't seem to find a way to do using boost.serialization.
Say with version 1, I want to serialize X Y and Z. These are hierarchical and expensive data structures. Now, with version 2, I do not need to create Y objects anymore. Yet, I still have to open version 1 files for backward compatibility. So, when loading version 1 files, I want to skip reading Y objects. How do I do that without having to create a temporary Y object that will be discarded later?
Of course this is the easiest way. Remember that after your user loads version 1 if he saves it again it will be saved in version 2 without the extraneous Y. So it will be just a temporary problem except in some unusual cases. For the case whereby a version 1 archive is read again and again you would have to make some special provision to update it.
(I'm particularly interested with XML archives. If I had control over the xml parser, that would simply mean ignoring everything from the current tag until the next matching tag is found).
I believe you do have the control you desire. Here's a sketch:
suppose object A includes memory variables x, y and z
specialize template for xml input archives and type A
void load (boost::archive::xml_iarchive & ia, A & a, const unsigned
version){
ia & BOOST_SERIALIZATION_NVP(x);
if(version == 1){
// the next data should look like