Re: [boost] [serialization] export macros

From: Christoph Ludwig (cludwig_at_[hidden])
Date: 2004-08-13 02:45:55

On Thu, Aug 12, 2004 at 07:03:57PM -0700, Paul Mensonides wrote:
> > From: boost-bounces_at_[hidden] 
> > [mailto:boost-bounces_at_[hidden]] On Behalf Of Rene Rivera
> 
> > [snip]
> > > a look at the preprocessor library but I couldnt come up with a 
> > > solution. Is there an alternative to the macros for 
> > registering types?
> > > (A sample program exhibiting what I am trying is attached.)
> > [snip]
> > > // Doesn't work (wrong number of macro arguments ):
> > > //  BOOST_CLASS_EXPORT( DerivedStatus< Algo< int, double > > );
> > 
> > Did you try using BOOST_PP_COMMA ?? For example:
> > 
> > BOOST_CLASS_EXPORT( DerivedStatus< Algo< int BOOST_PP_COMMA 
> > double > > );
> 
> Should be with nullary parentheses:
> 
> BOOST_CLASS_EXPORT( DerivedStatus< Algo<int BOOST_PP_COMMA() double > > );
> 
[...]
> The COMMA() trick will only work through one level of macro
> expansion.

Unfortunately, the serialization lib's export macros go through
several levels. Therefore, replacing the commas by BOOST_PP_COMMA()
does not help. (I tried it a few minutes ago.)

> Incidently, do we have a function argument mapping for the common case of this
> type of thing?
> 
> E.g.
> 
> template<class> struct pack;
> 
> template<class T> struct pack<void (T)> {
>     typedef T type;
> };
> 
> BOOST_CLASS_EXPORT( pack<void (DerivedStatus< Algo<int, double > >)>::type );

That did the trick! Great! 

I am not sure which of Boost's libraries is the most adequate place
for such a tool (preprocessor? mpl?), but it is certainly
valuable. And if / once there is such a tool in Boost, then the
documentation of macros that are likely to take classes genareted
from templates as arguments should refer to it. 

Regards

Christoph
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