[Boost-users] [serialization] Richer "tagged" fields and polymorphic archive types

Robert, First let me start off by thanking you for the excellent Boost Serialization library. I'm planning to use it as part of a new system I'm building at my place of work as a more flexible replacement for Rogue Wave's "saveGuts/restoreGuts". I've been able to implement my own archive types without too much of a struggle, and have been overall very impressed with the functionality of the library and its documentation. Now some background and then on to the questions :) I'm not sure if you are familiar with TIBCO's "Rendezvous" messaging middleware product (http://tibco.com/) or with the FIX protocol (http://fixprotocol.org/) but these are both commonly used in financial services applications. Rendezvous as a messaging transport and FIX as a general message convention and data dictionary. FIX also specifies a "session" layer used for communication, but thats out of scope here. Both Rendezvous (RV) and FIX support the concept of numeric field identifiers in their messages. In FIX, serialized messages look like TAG=VALUE\x01TAG=VALUE\x01... where TAG is an integer field ID and VALUE is the value associated with that tag and \x01 is an ASCII SOH character. In RV messages, fields may be given a name and/or an integer field ID. So it is pretty straightforward to represent a FIX message as an RV message (or vice-versa) if you always use these numeric IDs. Also, these "tagged" message formats facilitate interchange of data between different systems because they do not place stringent requirements on field ordering or even field presence in some cases. In the system I'm working on, the fundamental object types can all be mapped more or less directly to messages in the FIX specification. OK, so now onto the meat of the question. What I'd like to use in this application is something akin to NVP serialization for my objects, but which I'll call FIELD serialization. Every member of an object can be associated with a FIELD ID which would contain both a name and an integer ID (e.g. "Price" and 44). The universe of field IDs is more or less static and well-known. To this end I've created two utility classes called field_id and field. The field_id class is a std::pair and the template field class is a std::pair not unlike the nvp class. It provides methods to get the field's name, id, and value. There is also a template utility function "make_field(const field_id&, T&)" that creates a field object in the same way "make_nvp" creates an nvp. I have implemented a "tibco_oarchive" that provides a template "save_override(const field<T>&, int)" method, and this works fine if I am using template<typename Archive> serialization methods with my archive definition in scope, and if I write my serialization code using "make_field" instead of "make_nvp". But this, naturally, does *not* work if I try to use polymorphic archives, since the base classes here do not know anything about my "field" template, only "nvp". Additionally, my template-based serialization code will fail to compile with archive types that don't provide "save_override"s for my "field" template, which is all of the "standard" archive classes. What I'd like is to figure out some way to implement this tagged-field serialization scheme in a way that would be compatible with the polymorphic archive interface and that would (ideally) still compile with the existing archive implementations that don't know about my "field" class. This latter requirement is less important. The reason I'm leaning toward the polymorphic archive interface is that I'm sure we will need to adopt new wire-formats and middleware interfaces in the future. Keeping all the object serialization code in a library that doesn't require recompilation will make this process very easy. So, do you think you could offer any suggestions on how I might go about achieving this? Let me know if you need more information or clarification, and thanks for your help. -- Caleb Epstein