Re: [boost] [fusion-2] compile time pair

From: Andreas Pokorny (andreas.pokorny_at_[hidden])
Date: 2005-12-03 12:23:36

On Sat, Dec 03, 2005 at 03:56:09PM +0100, Andreas Pokorny <andreas.pokorny_at_[hidden]> wrote:
> On Sat, Dec 03, 2005 at 08:21:04AM +0800, Joel de Guzman <joel_at_[hidden]> wrote:
> > > There are entries in the map that do not require runtime data at all,
> > > for these entries all information is coverd by the second template 
> > > parameter of pair. And others like the dimension_tag which require 
> > > an instance of the second type stored in the container. 
> > > 
> > > How can I acchieve that with fusion?
> > 
> > If both the key and the data need to be just types, then what
> > immediately comes to my mind is an mpl::map. What am I missing?
> > Pure types == MPL. Half type/data == Fusion.
> 
> But I need both in the same associative container. What changes are
> required to make fusion deal with:
> template<typename F,typename S> struct ct_pair {
>   typedef F first_type;
>   typedef S second_type;
> };
> 
> It would be acceptable if fusion::at<key>(seq), or deref on a ct_pair causes 
> compile errors, provided that the pair entries in the same container
> still work. 

Oh, simpler than I thought. Kudos to you two, Dan and Joel. 
Fusion-2 is great, looking forward to write a review. I now use some
ct_pairs next to fusion::pairs in fusion::map. The meta stuff seems to work, 
only the runtime access functions deref and at fail to compile if they get 
applied on a ct_pair.

Regards
Andreas Pokorny