Re: [Boost-users] [serialization] Writing an old version of a class

From: Robert Ramey (ramey_at_[hidden])
Date: 2007-08-02 11:50:30

Pfligersdorffer, Christian wrote:
> Hello Robert, hello all,
>
> I know it is stated in the boost::serialization library documentation
> that per definition always the latest version of a class goes to the
> archive. I wonder if there is a way to change this behaviour and
> choose the version number for my class at runtime. Obviously this
> feature would be useful in a system of two dependent modules where
> either the producer or the consumer could by updated to a newer
> version without the other one being neccessarily updated too. Maybe
> this has already been discussed but I could not find anything about
> it on the web.
> However my strong suspicion is that there is no such option within the
> library and I will have to provide a solution within the affected
> classes.

I dismissed this issue when it was recently brought up for the first time.
I had never intended to provide an option for making "backward
compatible" so I had presumed that it wasn't going to be possible.

Well, some people kept bugging me and I did a little investigation
and found that it would be quite possible with just a little bit
of tweaking - and an amplified section in the documentation.
So I guess it will be done with 1.35.  FYI, the reason its doable
is just a side effect of the fact that I leaned hard on "symetry"
(I know I'm an atrocious speller) in order to conserve brain
surface area.  I suppose there is a lesson in there somewhere.

> Another thing: I specialize boost::archive::detail::heap_allocator<T>
> for my types to use my own memory management :-) Any objection to
> that?

The truth is I never really considered issue related to custom
allocators. I'm particularly interested in serialization of
collections which use custom allocators.  So I'm interested
in any experience in this area.

> Finally I want to thank Robert Ramey for his fabulous library and his
> always timely and helpful answers. I think from the user perspective
> he stands as a positive example for others.

I'm glad it's appreciated.  But I should say that I really enjoy spending
time on these kinds of posts.  I guess its the smart persons
alternative to internet chat forum.  I would like to encourage
those with questions/experience like this to get a little bit
more involved in contributing to boost.  Consider it therapy
for a day job where you spend all day with brain dead
managment and spend all your time hacking up the next fix
because "we don't have time" to do it right. or...

I would like to see more users contribute to demos/tests
to the "case studies" section of the serialization documentation.
A number of ideas have been presented on this list but
I don't have time to persue them all.  Here are a few.

a) serialization of collections with custom allocators
b) serialization of function objects
c) automatic generation of an archive editor -
(actually I've made progress on this myself)
d) backward compatible archives - will require
tweak in library but also special practice for
serialization functions.
e) composition with special stream buffers
for increasing speed, implementing compression
etc.

What's in it for you?  You get full authorship credit
on your case study. It looks good on your
resume.  It makes you a part of the world's most
exclusive club of C++ programmers.  You get
the satisfaction of knowing that you've done
something "almost perfect".  You get the
satisfaction of knowing that perhaps
thousands of other programmers know, use
and appreciate your work.  In short you
get almost all the satisfaction that goes with
being an "official" boost developer without the
real pain (dealing with bjam, build, etc.) Rather
than suffering a review process which is really
frustrating, public and often unpleasant, you only
have to pass one reviewer (me) in private.  You get
to interact with people who work with your code
and get a chance to tweak it from time to time
to fix bugs, clarify documentation, etc.
In short you get most of the satisfaction of being a boost
developer and avoid most of the pain.  (Of course
to get the full boost experience you have to undergo
the full pain of a review and all the rest - but most
people don't have the time for that)

So there you are.

Robert Ramey