Re: [Boost-users] serializable any

From: troy d. straszheim (troy_at_[hidden])
Date: 2008-08-10 13:38:22

Robert Ramey wrote:
> 
> Hmm - I don't think you're missing anything.  You're right, if you use
> typeid() you don't have to "predeclare" anything - but it can't be used to
> create portable archives.  That's the whole justification for creating
> BOOST_CLASS_EXPORT...
> 
> Basically, either one has to do one of the following:
> 
> a) except the fact that in some sense one has to "declare" any<U> as being 
> "exportable"
> b) eliminated the heretofore enforced requirement that archives be portable.
> 
> So far we've done a) - hence shared_ptr serialization has a macro (whose 
> name
> I forget) to handle a situation.  Leveraging on this concept - and 
> diminishing
> the proliferation of special cases would argue for something similer in 
> other special
> cases - like boost::any
> 

OK, I wasn't missing anything.  The Original Poster (OP) wanted to
avoid this 'predeclaration', I thought we were going that direction, got confused.

So you'd need to expose the internals of any to the world, as the
export macro has to expand to something that refers to boost::any::holder<T>,
which is private.  Friending boost::serialization::access
any won't do it, as boost::serialization::access isn't the one doing the
registration, and the expansion of the export macro
will appear in some arbitrary location chosen by the user.  So for export of boost::any
that holds type V, you'd need

   ::boost::serialization::any_export<V>

where any_export is *also* a friend of boost::any, and it registers any::holder<V>
with serialization::detail::guid_initializer<any::holder<V> >.

or something like that.   Maybe one can make this work just by forward declaring and friending
boost::serialization::access and boost::serialization::any_exporter inside boost::any.
Dunno, maybe I'll try it.  It'd be good to know if those modifications would be acceptable first.

-t