[boost] [serialization] export.hpp changes from 1.37 to 1.38

Subject: [boost] [serialization] export.hpp changes from 1.37 to 1.38
From: Chard (boost_at_[hidden])
Date: 2009-02-13 19:01:34

The BOOST_CLASS_EXPORT.. macros have been moved into a detail namespace
(1.38) from a (public) anonymous namespace (1.37).

I'm guessing that the reasoning for this was in order to avoid many
definitions of the class singletons.  However, this appears to have enforced
that all of the guids (for all archive types) now have to reside in a single
compilation unit.

The attached code illustrates the limitation; this compiles under 1.37 but
results in duplicate symbol definitions in 1.38 (with MSVC7.1).  It worked
with 1.37 because the anonymous namespace ensured no symbol clashes, but now
the symbols are all in the same namespace.

The example shows a case where two archive types (xml and binary) might be
in use.  The obvious solution to this (simple) case would be to just use a
single compilation unit, which brings in the guids for both binary and xml.
However, turning a blind eye to the 'untidiness', this fix does not help
with the project we're working on.

In our project, there is not just a simple type being serialized; there are
a lot more classes and a bit of mpl thrown in.  This actually resulted in
breaching the COFF symbol limit (approx. 65k) with MSVC7.1, so we were
forced to split the serialization.  In fact, we had to split both the save
and load parts of the binary serialization.

Our current workaround is to use the archive.register_type<...> method, and
ignore the export macros, but this does mean ensuring all types are covered
(as described in the documentation).