Re: [Caml-list] extending a type with Marshal

[skaller <skaller@ozemail.com.au>]

On Thu, 2003-10-09 at 07:22, Ker Lutyn wrote:
> Marshal provides a convenient way to pass information between
> components. It requires that types be the same at either end. But for
> multi-machine production systems that must serve traffic continuously,
> you cannot count on upgrading all your systems simultaneously.
> 

If you have p2p connection: Negotiate.
That's the traditional solution: used by modems,
for example.

Fixing a negotiation protocol isn't hard.

IMHO the hard part is identifying 'versions'
and 'capbilities'. Probably the best way is
to use a string encoding (and use a parser).

Nastiest example I can think of is requesting a font.

Note this suggestion requires both servers and clients
to maintain capability to handle several 'old' versions.

This isn't extension of the Marshalled data, rather
quite distinct data for each 'version' is possible,
so the solution seems more general: the cost is extra
handshakes -- how expensive that is depends on how long
the agreement lasts (until explicitly refreshed? until
end of session? only for a single data fetch?)


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