RE: [boost] Re: Small thing: yes_type and no_type made public?

From: Hartmut Kaiser (hartmutkaiser_at_[hidden])
Date: 2003-01-08 14:52:56

Paul Mensonides wrote:

> > I think, that using the PP library will give us the possibility to
> > configure the maximum number of required sizetype typedefs. I've
> > attached a version of the yes_no_type.hpp, which does so by
> defining a
> > constant 'BOOST_MAX_SIZETYPE_COUNT' if this constant isn't already
> > predefined by the user.
> >
> > Regards Hartmut
>
> Just a small point, you should include
> <boost/preprocessor/repetition/repeat.hpp> after your normal
> include guard.
> While it won't change the result, it is a waste of time to
> include it prior
> to the include guard.  One other slight problem is that
> BOOST_PP_REPEAT goes
> from 0 to N, which will cause you to get this declaration:
>
> typedef char (&size0_t)[0];
>
> ...which is illegal.

Thanks for pointing this out. I'm only at the beginning with the PP
library.

> Separately, I don't particularly think that this is a good use of the
> pp-lib.  You can achieve the effect you want easily:
>
> template<int I> struct size_descriptor {
>     typedef char (& type)[I];
> };
>
> typedef size_descriptor<1>::type yes_type;
> typedef size_descriptor<2>::type no_type;
>
> ...or something similar, which solves the problem once and for all.

Nice idea.

Regards Hartmut