Re: [Boost-users] [serialization] skipping data

From: Joel de Guzman (joel_at_[hidden])
Date: 2006-07-10 01:55:20

Kim Barrett wrote:
> At 9:13 AM +0800 7/10/06, Joel de Guzman wrote:
>> 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?
>>
>> (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 think such a simple approach will not work in general. Consider
> the case where
> 
> 1. your Y contains a pointer to P
> 2. pointer tracking is enabled for P's type
> 3. the occurrence of P in Y is the first occurrence within the archive
> 4. there are later occurrences of P in the archive after Y
> 
> If you simply discard everything involved in constructing Y, you will
> discard the information needed to construct and record P, and those
> later occurrences will be left dangling.

Don't worry. I know what I am doing :) Trust the programmer ;)

Regards,
-- 
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net