Robert Ramey wrote:
Joel de Guzman wrote:
Peter Dimov wrote:
Joel de Guzman wrote:
Peter Dimov wrote:
There might be a possibility that Y is already obsolete at version 2. Sure you can "emulate" it through the proxy thing, but then again that's less than ideal. I simply want to skip some data and I can't do it with Boost.Serialization. I can do it with simple streams, for example, by prepending the data with a length (in bytes). I can also do it with XML by ignoring everything in between the current tag and its matching end tag. Rene (Rivera) noted that some archive types also allow it. For example, IFF (http://en.wikipedia.org/wiki/Interchange_File_Format) allows it through chunking. "Because the spec includes explicit lengths for each chunk, it is possible for a parser to skip over chunks which it either can't or doesn't care to process."
IMO, this is a valid use case that Boost.Serialization can address, at least, for archive forms that allow it. Perhaps a SkippableArchive concept? IMO, the ability to skip is a prerequisite for transparent versioning.
It would be feasible to make an archive type which would support this. (I believe xml archives could do it now.) But that would require extra information in the archive that would otherwise be unnecessary. Natually this would provoke howls of protest were it to be included in every archive. So we're back to a "special purpose" archive or archive adaptor which adds the extra information to every archive. Of course this wouldn't help with version 1 archives which presumably have already been written.
No, the "imaginary" version 1 file has not been written yet. I am programming in the future tense :) I also believe that the XML archive format *can* do it now, which is why I am asking ;) And, as I mentioned, I'm particularly interested with XML; but I do not want to subvert the Boost.Serialization interface. Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net