Re: Re: [boost] [serialization] export macros

From: Christoph Ludwig (cludwig_at_[hidden])
Date: 2004-08-14 07:48:57

On Fri, Aug 13, 2004 at 07:17:33PM -0700, Paul Mensonides wrote:
> > From: boost-bounces_at_[hidden] 
> > [mailto:boost-bounces_at_[hidden]] On Behalf Of Christoph Ludwig
> 
> > However, this problem is by no means specific to the 
> > serialization library.
> 
> No, it isn't.
> 
> Note also that the solution is incomplete.  Types have to not only be capable of
> being argument types (e.g. not 'void'), but they also must remain unchanged by
> simply being an argument type (e.g. array declarations decay to pointers,
> function types are transformed to pointer to function types).  In other words,
> the solution only works for the common case.

Just for clarification: You say that in the following

  template<class> struct pack;

  template<class T> struct<void (T)> {
    typedef T type;
  };

  MY_MACRO(pack<void (void)>::type)
  MY_MACRO(pack<void (MyTemplate<int, int>[10])>::type)

both macro expansions won't work (or more precisely, result in code
that will fail or yield unwanted results when compiled)? Hm, I
probably should peruse my copy of the book by Vandvoorde and Josuttis
again, but this makes kind of sense.

IIUC this might be a problem if you need to be able to pass *any* type
to a macro. But in the case of the serialization lib it's always a
class type that needs to be registered. And neither void nor
MyTemplate<int, int>[10] is a class type. Are you aware of any
examples where above approach won't work when calling the
serialization lib's export macros?

> > Whenever you have a macro that takes a 
> > classname you may face this issue. One could consider it a 
> > (inherent) preprocessor shortcoming solved by means of 
> > template programming.
> 
> As an aside, if you have a conforming preprocessor, the problem is solveable
> with the preprocessor (especially so with variadics).

Is it solveable with the preprocessor as defined in the C++ standard
from 1998? Or do you need the C99 preprocessor?

Regards

Christoph
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