Emil Dotchevski wrote:
If X is usable without serialization, users shouldn't be forced to also
link to the serialization library, just because of this dependency. (In the particular case I have in mind this dependency was controlled by a preprocessor macro. That's not very practical, since packagers surely won't provide two sets of packages for X, one with and one without this dependency.)
Thus, I'd suggest to encapsulate the X-serialization functionality into a separate library (may be header-only), such as X_serialization.hpp etc. Then I can still use X stand-alone, and drag in the rest whenever I need it.
This has been discussed before. You don't need X_serialization.hpp, if you don't use BOOST_CLASS_EXPORT. See http://www.archivesat.com/Boost_developers/thread2900871.htm.
I'm not sure how relevant that is. If X.hpp contains serialization-related code, it surely needs to include serialization header files, too, to drag in any relevant declarations. Thus there is a dependency from X to serialization.
You need no declarations because the serialization is implemented as a function template: class foo; template<class Archive> void serialize(Archive & ar, foo & x, const unsigned int version) { ar & x.bar; .... } The above code compiles without including any boost serialization headers. I have not used boost serialization (I have my own serialization library), but as far as I can see the reason why foo.hpp that uses boost serailization needs to include serialization headers, is to be able to use BOOST_CLASS_EXPORT. For me this is good enough reason not to use BOOST_CLASS_EXPORT. Emil Dotchevski