[boost] [serialize] xml archives and versioning

From: Russell Hind (rh_gmane_at_[hidden])
Date: 2004-10-20 09:39:06

The header of our xml archive looks like this:

<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
<!DOCTYPE boost_serialization>
<boost_serialization signature="serialization::archive" version="3">
<CoatingScanConfig class_id="0" tracking_level="0">

The object written as CoatingScanConfig didn't have a class version 
specified (and therefore there isn't one in the header).

When writting this class, the version parameter is passed in to the 
serialize() method is 0 for the class, but when reading it, the version 
number is subsequently passed in as 3 (which looks like the archive 
version).  Should it not be 0 also?

Is 0 a valid version number for a class?  If I specify the class version 
as 1, then reading and writing both get '1' as the version, but if I 
don't specify a version, or I specify 0, then writing gets 0, but 
reading gets '3'.

If 0 isn't valid, then could there be a static_assert catching this?

And a quick usage question: If a class isn't versioned, is an inherent 
'version 0' written to the archive so that a version number of 1 can be 
applied to the object later when it is modified, or do objects need to 
be given a version number from the start?

Thanks

Russell