Andreas Pokorny wrote:
On Sat, Dec 03, 2005 at 03:56:09PM +0100, Andreas Pokorny <andreas.pokorny@gmx.de> wrote:
On Sat, Dec 03, 2005 at 08:21:04AM +0800, Joel de Guzman <joel@boost-consulting.com> 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.
Ah yes :) That's because fusion::map is not tied to a specific pair implementation. In fact it is ignorant of the fusion::pair. "boost/fusion/core/pair.hpp" is included in map only as a convenience to users. Regards, -- Joel de Guzman http://www.boost-consulting.com http://spirit.sf.net