Re: [Boost-users] [serialization] conditional serialization of membersand base classes

From: n.torrey.pines (n.torrey.pines_at_[hidden])
Date: 2007-02-22 18:43:14

Hi

I'm not actually worried about throwing the rest of the archive out of 
sync, because the whole file will contain only one instance of "b". When 
b::m_a does not match what's in the archive, I'll just give up on 
loading and close the file.

However, I'm worried about other issues, like the ones mentioned in the 
tutorial under "Derived Classes": versioning problems, etc. Can I 
serialize with boost::serialization::base_object and deserialize with "&" ?

Thanks

Robert Ramey wrote:
> An interesting case.  But I don't see how this could be done without 
> enhancing the library in some non-obvious way. .
> 
> Then general problem is that the seialization library writes a serial stream 
> of bytes.  So you can't skip a piece without throwing things out of sync. 
> But you don't know how long something is until it's serialized and then its 
> too late.
> 
>  You might be able to do it for some special cases though
> 
> Robert Ramey
> 
> n.torrey.pines wrote:
>> Hi
>>
>> The logic I want to implement is:
>> * b contains a
>> * when saving b, save a, followed by other data
>> * when loading b, load a into a temporary, if it matches b.m_a, load
>> other data
>>
>> Would you expect the following code to work?
>>
>> class b {
>>     a m_a; // a is serializable
>>     vector<int> m_v; // other data
>>
>>     template<class Archive>
>>     void save(Archive& ar, const unsigned version) const {
>>         ar & m_a;
>>         ar & m_v;
>>     }
>>
>>     template<class Archive>
>>     void load(Archive& ar, const unsigned version) {
>>         a tmp;
>>         ar & tmp;
>>         if(tmp == m_a) ar & m_v;
>>     }
>>
>>     // ...
>> };
>>
>> Now, what if b is derived from a instead of containing it? Would this
>> work?
>>
>> class b : public a {
>>     vector<int> m_v; // other data
>>
>>     template<class Archive>
>>     void save(Archive& ar, const unsigned version) const {
>>         ar & boost::serialization::base_object<a>(*this);
>>         ar & m_v;
>>     }
>>
>>     template<class Archive>
>>     void load(Archive& ar, const unsigned version) {
>>         a tmp;
>>         ar & tmp;
>>         if(tmp == static_cast< const a& >(*this)) ar & m_v;
>>     }
>>
>>     // ...
>> };
>>
>> Thanks!