Re: [boost] [GTL] redesign checked into sandbox

From: John Femiani (JOHN.FEMIANI_at_[hidden])
Date: 2008-05-10 09:24:38

Bruno wrote:
...
> 
> Yep precisely because the concept literally says "there must 
> exist a specialization of point_traits with X such that this 
> code is valid".
> It's finally as much a "point traits concept" as a "point concept".
> Maybe it would be better to have X being the specialized point_traits?
> It would require an additional point_type typedef in the 
> point traits and would give something like:
> 
> template <class X>  // X is a point_traits struct PointTraits {
>   typedef typename X::coordinate_type ctype;
>   enum { ccount = X::coordinate_count };
> 
>   template <int I, int Count>
>   struct dimension_checker
>   {
>       static void check()
>       {
>           const typename PT::point_type* point;
>           ctype coord = X::template get<I>(*point);
>           typename PT::point_type* point2;
>           X::template get<I>(*point2) = coord;
> 
>           dimension_checker<I+1, Count>::check();
>       }
>   };
> 
>   template <int Count>
>   struct dimension_checker<Count, Count>
>   {
>       static void check() {}
>   };
> 
>   BOOST_CONCEPT_USAGE(Point)
>   {
>       dimension_checker<0, ccount>::check();
>   }
> };
> 
> Then, requirements inside algorithms would be done this way:
> 
> template <class P>
> BOOST_CONCEPT_REQUIRES(
>    ((PointTraits<point_traits<P> >)),
>    (void))
> function_requiring_a_point(const P& p)
> {}
> 

Well, if we agree that traits at least have the _potential_ to cause an
issue then why make the approach _more_traits based?

> It doesn't sound clearer to me though... If it's not what you 
> were expecting, could you propose another concept definition?
>

I like most of what you have, and I am trying to get you guys to do the
thinking so I dont have to ;)

I'll work something up and send a link when I get a chance, but I think
that it will take some work and testing.

-- John