I think there is a significant issue with your proposed extension mechanism: an archive can only contain a single extension object at a time. Consequently, if two types require different extension objects, they cannot both be serialized using the same archive. In particular, if say flyweight requires some special extension object, and shared_ptr requires its own special extension object, it won't be possible to serialize both using the same archive. It seems,
Hi Jeremy, ----- Mensaje original ----- De: Jeremy Maitin-Shepard <jbms@cmu.edu> Fecha: Lunes, Octubre 8, 2007 10:15 pm Asunto: Re: [boost] [serialization] Proposal for an extension API to theArchive concept Para: boost@lists.boost.org therefore,
that in practice there would have to be a single standardized extension object,which is either in use or not in use for a particular archive.
My proposal allows for any type to register and use its own helper object: note that the proposed extension interface: a.get_extension_obj(p); a.set_extension_obj(p); is *not* meant to be public; quoting from http://tinyurl.com/2tuucq : "These expressions are reserved for the internal usage of Boost.Serialization and thus must not be called by user code." It is then Boost.Serialization that adjoins its own extension object to an Archive and publicizes a helper API based upon this internal object: template<typename Archive> void insert_helper( Archive& ar, const extended_type_info* eti, shared_ptr<void> & sph) { // get the extension object or create a new one if this // is the first time shared_ptr<void> ext_obj=ar.get_extension_obj(); if(!ext_obj){ ext_obj.reset(new extension); ar.set_extension_obj(ext_obj); } extension& ext=*ext_obj; // forward to the extension object ext.insert_helper(eti,sph); } So, each distinct T can register its separate helper object more or less like this: serialization::extended_type_info* eti= serialization::type_info_implementation<helper<T> >:: type::get_instance(); shared_ptr<void> sph; insert_helper(ar,eti,sph); ... Did I make myself clearer now? Joaquín M López Muñoz Telefónica, Investigación y Desarrollo