Re: [Boost-users] Developing a new boost archive

Subject: Re: [Boost-users] Developing a new boost archive
From: Larry Evans (cppljevans_at_[hidden])
Date: 2012-02-15 14:30:21

On 02/15/12 12:38, Robert Ramey wrote:
> Roberto Fichera wrote:
>> On 02/15/2012 06:01 PM, Robert Ramey wrote:
> 
>>> c) Even worse, the aproach above would make even text archives
>>> non-portable between platforms.  Of course this is a non-starter.
>>> So you might want to re-think your approach above.
>>
>> I agree totally with you! Actually my constraint is to use gnu
>> toolchain,
>> MSVC and pathscale compilers and eventually LLVM, but this one is not
>> a priority at moment. But, any way still the problem of the demangling
>> portability.
>>
>> By the way, how did you solve the problem ... if you solved it,
>> indeed ;-) ?
> 
> It is already solved portably via the "export" functionality.  Look
> it up in the documentation.
> 
> Robert Ramey
Hi Robert,

Looking at:

 http://www.boost.org/doc/libs/1_48_0/libs/serialization/doc/serialization.html#derivedpointers

and reading:

   The system "registers" each class in an archive the first time an
   object of that class it is serialized and assigns a sequential
   number to it. Next time an object of that class is serialized in
   that same archive, this number is written in the archive. So every
   class is identified uniquely within the archive. When the archive
   is read back in, each new sequence number is re-associated with the
   class being read. Note that this implies that "registration" has to
   occur during both save and load so that the class-integer table
   built on load is identical to the class-integer table built on
   save. In fact, the key to whole serialization system is that things
   are always saved and loaded in the same sequence. This includes
   "registration".

And paraphrasing part as:

   So every class is identified by this uniquely assigned sequential
   number within the archive.

Then I'd infer that this "uniquely assigned sequential number" play
a role similar to the role of the result of:

   abi::__cxa_demangle( typeid( T ).name(), 0, 0, NULL );

in Roberto's post:

  http://article.gmane.org/gmane.comp.lib.boost.user/72805

As you mention, Roberto's method is not portable between platforms
(where, of course, a different compiler or even different version
of the same compiler would be a different platform).

OTOH, as you also mention in the above quote, boost serialization
requires:

   things are always saved and loaded in the same sequence.

Roberto, would that be a problem for you?

-regards,
Larry