Re: [boost] Refactoring a library for header-only or linked library?

Subject: Re: [boost] Refactoring a library for header-only or linked library?
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-04-01 10:59:28

Le 01/04/12 10:54, Paul A. Bristow a écrit :
> I am considering refactoring a (potential Boost) library separating declarations and definitions
> into two sets of files with the objective of  reducing compilation times and allow it to be used as
> header-only or linking with a pre-built library.
>
> Is there is best/Boost way of doing this?
>
> Is there a Boost library that I should use as a model?  ASIO?
>
> Should I call the definition files .cpp or .ipp?
The definitions should be on a header file and  .ipp or .hpp is good for 
me. Boost.Chrono uses .hpp header files.
> Should definition files go in libs/src or in boost/?
Boost.Chrono includes them in boost/chrono/detail/inlined directory. 
libs/xxx/src should not work as an installer don't need to install this 
directory.
>
> How should I control the header-only/library switch?
Boost.Chrono uses a macro to BOOST_CHRONO_HEADER_ONLY as the goal was to 
make the library header-only.

#ifdef BOOST_CHRONO_HEADER_ONLY
#include <boost/config/abi_suffix.hpp> // pops abi_prefix.hpp pragmas
#else
#include <boost/chrono/detail/inlined/chrono.hpp>
#endif

The config.hpp file contains

#ifdef BOOST_CHRONO_HEADER_ONLY
#define BOOST_CHRONO_INLINE inline
#define BOOST_CHRONO_STATIC inline
#define BOOST_CHRONO_DECL

#else
#define BOOST_CHRONO_INLINE
#define BOOST_CHRONO_STATIC static
...
#endif

Note that this has some relation with the macros BOOST_XXX_STATIC_LINK  
and  BOOST_XXX_DYN_LINK which are exclusive.

Your goal been different the macro should be named differently. In 
addition what is the default also need to be taken in account.

In the case of Boosy.Chrono I prefered to state explicitly the intent of 
the User via BOOST_CHRONO_HEADER_ONLY even if it could be deduced when 
BOOST_CHRONO_STATIC_LINK  and  BOOST_CHRONO_DYN_LINK are not defined.

HTH,
Vicente