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

Subject: Re: [boost] Refactoring a library for header-only or linked library?
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2012-04-12 10:14:41

> -----Original Message-----
> From: boost-bounces_at_[hidden] [mailto:boost-bounces_at_[hidden]] On Behalf Of Vicente J.
> Botet Escriba
> Sent: Sunday, April 01, 2012 3:59 PM
> To: boost_at_[hidden]
> Subject: Re: [boost] Refactoring a library for header-only or linked library?
> 
> 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.

Thanks for this advice.  Better advice might have been "Don't try this at home!" ;-)

The complexity of templates and their instantiation means that breaking the ODR proves unavoidable.

So I am reverting to the inclusion model :-(

But thanks anyway.

Paul

---
Paul A. Bristow,
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