Hartmut Kaiser wrote:
Stefan,
Appologies from me, too, as now we are getting even further from the original topic.
I have seen at least one case where it was indeed X.hpp that introduced the dependency to serialization code. However, this generates another problem:
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.
I'm not sure, if this is always possible.
This isn't a new debate, but I believe a separate user specified header is the correct solution. This is how date-time is done and others should be as well. As I recall prior discussions, not all libraries have been factored that way -- I think multi-index isn't -- Joaquin had some good reasons. Anyway, it's a bit more effort, but because of the serialization design it should always be possible do have external serialization functions. In general serialization requires a pile of extra includes that should be avoided if possible.
PS: the library I'm thinking of is boost.wave, and there serialization was dragged in whenever BOOST_WAVE_SERIALIZATION is defined.
As far as Wave is concerned, the mentioned macro has no influence on the code generated for the library. You always can define BOOST_WAVE_SERIALIZATION to zero when compiling your code, even if the library was compiled with BOOST_WAVE_SERIALIZATION=1. The generated library has no dependency on Boost.Serialization.
Seems to me that unless it's essential to library function serialization support should always be turned off by default. Jeff