[boost] Re: MPL include problem with BOOST_PP_ITERATE

From: Hugo Duncan (hugoduncan_at_[hidden])
Date: 2003-01-24 17:24:11

On Fri, 24 Jan 2003 13:53:00 -0800, "Paul Mensonides" <pmenso57_at_[hidden]> wrote:
> 
> ----- Original Message -----
> From: "Hugo Duncan" <hugoduncan_at_[hidden]>
>

> > I am including files using BOOST_PP_ITERATE.  One of the files
> > that I include happens itself to include boost/mpl/list.hpp.
> 
> I'm not sure what you mean here.  If you are iterating over a file (or
> section of a file) with the file-iteration mechanism.  That iterated text
> should *never* include regular headers.

Paul, 

I was not aware of that restriction - it doesn't seem to be mentioned in the docs.

> [Snipped example]
> 
> It is defined when the file-iteration mechanism is iterating over a file.
> Its purpose is to distinguish between a normal inclusion and an "iteration"
> inclusion so that the same file can iterate over itself.  When a file that
> is iterated includes other files *during an iteration*,
> BOOST_PP_IS_ITERATING is still defined and the other files probably won't
> know how to handle it. (<boost/mpl/list.hpp> is one example of this.)  The
> solution is simply to not include any files during a particular iteration.

This, for me, is a nuisance, as the files that I am including through ITERATE
are included individualy at times, and could add header dependencies
that I do not know about elsewhere.

The reason for my using ITERATE is to be able to provide an
extensible list of files to include as a single
extension/maintenance point for my library, so having to write 2.hpp
reduces the incentive to use ITERATE in the first place.

I still think that this could be solved by checking something like
the following in <boost/mpl/list.hpp>

  #if !BOOST_PP_IS_ITERATING || !BOOST_MPL_PREPROCESSING_MODE

Hugo