Re: [boost] [serialization][trunk] please bring us archive helpers back

From: Robert Ramey (ramey_at_[hidden])
Date: 2007-09-05 11:17:58

I put the archive helper in as an ad hoc solution to a particular problem.
I was always unsatisfied with it as I didn't like the idea of decorating
the main serialization library code with special cases.  Its my belief
that this is what makes libraries die of old age.  However, at the
time it seemed expedient so I included it for this one case
(shared pointer) and left it undocumented on purpose.

Eventually I found what to me is a much better solution
and this is implemented in the next release.  This is
to use multiple inheritance to add the helper in as a mix-in.
This is the way I plan to support this kind of thing in
the future.  It doesn't change the published API of the
serialization library itself.  However I will add a
section in the documentation - if its not already there
describing this technique.

I believe that using mix-in to ad helpers will be
equivalent to adding them in at runtime as they are now.

I included the shared_ptr helper mix-in in the in the
library in order to not change the current api and
in recognition of shared_ptrs priviledged status
as a boost component.

I didn't expect anyone to notice this change, as
no one had posted a problem which required
helpers and it was undocumented.

Robert Ramey

Joaquín Mª López Muñoz wrote:
> Hello,
>
> Boost.Serialization 1.33-1.34 introduces the notion or "helpers" to
> the Archive
> interface by means of the member functions:
>
>   void lookup_helper(
>     const extended_type_info* const eti,
>     shared_ptr<void>& sph);
>   void insert_helper(
>     const extended_type_info* const eti,
>     shared_ptr<void>& sph);
>
> which allow the user to make an archive instance store arbitrary
> helper objects
> associated to any given type. This helper interface is used to
> implement
>
> serialization of boost::shared_ptr in a non-intrusive way, which was
> impossible
> for former versions of Boost.Serialization. This is a wonderful
> addition
>
> to the library because not only solves the old problem with
> serializating
> shared_ptr but also serves as a general utility for implementing
> complicated
> serialization schemes, notably those in which internal resources are
> serialized
> which cannot be directly manipulated from the class public interface.
>
> I have used archive helpers to good effect in implementing an
> otherwise unfeasible serialization algorithm for a library I'm
> writing, but when I moved
> from Boost 1.34 to the SVN trunk I discovered to my dismay that this
> (admittedly undocumented) feature has been removed in favor of an
> ad-hoc
>
> extension of the Archive interface (internally based on something
> resembling
> the former helper code) to specifically allow serialization of
> boost::shared_ptr.
> IMHO this is a step back because it singles out shared_ptr as a type
> receiving special attention (vg. what will happen with
> std::tr1::shared_ptr,
> will the interface be augmented again to cope with this?) and
> primarily because it deprives us developers from a very very powerful
> tool.
>
> Could the helper interface please please be brought back to
> Boost.Serialization? Thank you,
>
> Joaquín M López Muñoz
> Telefónica, Investigación y Desarrollo
>
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