Re: [boost] [proto] design of expr<>

From: Markus Werle (numerical.simulation_at_[hidden])
Date: 2008-03-10 12:38:07

Steven Watanabe <watanabesj <at> gmail.com> writes:

> 
> AMDG
> 
> Markus Werle wrote:

> > Sorry if I do not get that one.
> >   
> 
> The definition of expr is something like:
> 
> template<class Tag, class Args, int Arity = Args::arity>
> struct expr;
> 
> template<class Tag, class Args>
> struct expr<Tag, Args, 0> {
>    typename Args::arg0 arg0;
> };
> template<class Tag, class Args>
> struct expr<Tag, Args, 1> {
>    typename Args::arg0 arg0;
> };
> template<class Tag, class Args>
> struct expr<Tag, Args, 2> {
>    typename Args::arg0 arg0;
>    typename Args::arg1 arg1;
> };
> 

OK, and what is the advantage of the 3rd template argument Arity then?
AFAICS this is needed for the BOOST_PP_ITERATION magic, but strictly speaking
it is not necessary for the data _representation_, right?

Also I feel very uncomfortable about those typedefs above ... 
can't we get along accessing by index when in need for it?
 

Markus