On 09/01/2011 11:45 PM, Martin Bidlingmaier wrote:
Ok, so obviously the proposed version won't work when instances of boost::any cross dll borders. I see only one possible way out without breaking existing code (and still use the new version, if it is considered superior): Let the user explicitly declare he wants to use the version with statics by introducing a new configuration macro, e.g. BOOST_ANY_NO_DLL_CROSSING, or use an existing macro that does the same thing. If not defined, type_info comparsion would be used.
I don't really like the macro idea because it breaks ABI. Consider this. On Linux, and probably other UNIX systems, Boost libraries are provided as shared libraries. So if I use system Boost.ProgramOptions, for instance, I'm linking with a shared library. But Boost.ProgramOptions uses boost::any and AFAIR it passes it across library boundaries. So my application will not be able to use the optimized boost::any. I understand that there are cases when you link with no shared libraries and eager to squeeze that little extra bit of performance. But honestly, does that change really make a difference in the context of your application? And if it does, perhaps your case is special enough to create a separate component, say, local_any? Or take a different approach in your design altogether?