Re: [boost] [fusion]variadic template implications forcontainers(was Re: Variadic Templates Redux

From: Andy Little (andy_at_[hidden])
Date: 2006-09-28 12:13:32

"Doug Gregor" <dgregor_at_[hidden]> wrote in message
news:11FDF23E-AE83-484F-B34E-D03829821B55_at_cs.indiana.edu...
>
> On Sep 28, 2006, at 3:20 AM, Andy Little wrote:
>> And a Question to Doug Gregor Does ConceptGCC support decltype and
>> auto? Please
>> note: this is Not a feature request, just a simple question! :-)
>
> No, we don't have support for decltype or auto in ConceptGCC.
>
> Of course, you can fake decltype with concepts, if you want:
>
>   auto concept Callable2<typename F, typename T1, typename T2> {
>     typename result_type;
>     result_type operator()(F, T1, T2);
>   }
>
> Callable2<F, T1, T2>::result_type tells you the type returned by
> calling an object of type F with arguments of types T1 and T2.

I was just looking at the tutorial, wondering about whether I could do that...

...And if I couldnt,  I was going to suggest that I should be able to. :-)

>> Of course if I really want it, then I guess I ought to try sorting
>> it out myself
>> though shouldnt I?  :-)
>
> If be "sorting it out myself" you mean implementing decltype and auto
> in GCC, then "yes"! :)

hmm... (actually that Was a feature request... ;-) )  *Interesting* idea though,
trying to hack Gcc....  very foolhardy IMO, unwise, very unwise...

 :-)

Am I right that I can add  conditional Concept support to headers by :

 # ifdef __GXX_CONCEPTS__

... concept stuff

?

And what happens if I have for example a Numeric concept (float, int,
boost::numeric::interval) and I want to make Integer a 'member'( model?). How
would that work? And integer is also a fundamental type of course

Would I be able somehow to express that I don't want potentially 'lossy'
division. e.g int / int ?

Anyway  I will have to see how well it works in my physical quantities library.
I'm glad I finally got round to trying it out :-)

regards
Andy Little