Re: [boost] [serialization] Enhancing Archives with Archve Adaptors

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-11-27 12:08:00

Robert Ramey wrote:

> Changing the names a little bit for clarity, I always anticipated
> archive developers would use something like the following:
>
> template<class T>
> void save(boost::hpc_archive &ar,  const std::valarray<T> & t...)
> {
>     const unsigned int count = t.size();
>     ar << count;
>     save_array(ar, get_data(t),t.size());
> }
>
> This would apply the save_array enhancement to all classes derived
> from hpc_archive.  In fact I would expect that this is the way people
> are doing it now.

This doesn't work well for several reasons. First, the static type of ar is 
hpc_archive, so hpc_archive must be a polymorphic archive base, and this is 
not desirable since it's High Performance.

Second, if you add an overload for std::vector:

template<class T>
void save(boost::hpc_archive &ar,  const std::vector<T> & t...)

the version in the Serialization library will take precedence since it's an 
exact match for the archive argument, and the overload above requires a 
derived to base conversion.

Even if it did work, I don't see in which circumstances a class author would 
like to _not_ take advantage of the save_array enhancement. Ideally, he 
should just call save_array in save, without restricting it to a specific 
set of archives. I don't see what you gain by denying him this opportunity - 
assuming that it can be provided without negative consequences for the 
current code base or existing archive formats.