Re: [Boost-users] [fusion] is there anything resembling a joint_view of 2 maps?

22 Oct 2009

...
Either way, for now you can workaround your issue by providing your own 
extension implementations for 
fusion::extension::category_of_implfusion::joint_view_tag, 
fusion::extension::has_key_implfusion::joint_view_tag and 
fusion::extension::at_key_implfusion::joint_view_tag, or, even better, 
wrap the joint_view up in another view which implements both (forward 
and associative) extension backends.
Thanks, but the workaround you are suggesting is not obvious to me. 
Maybe you can help? I have started here :

         template <>
         template
         struct at_key_impl::apply<
             joint_view,Key
         >
         {
             typedef joint_view jv_;

             typedef fusion::result_of::has_key has_key1_;
             typedef typename mpl::if_<
                 has_key1_,
                 Seq1,
                 Seq2
             >::type seq_;

             typedef typename result_of::at_key::type type;

             static type
             call(jv_& m)
             {
                 // return m.at_impl(mpl::identity<Key>());
		????

             }
         };