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

20 Sep 2009

      Hi All,

I am wondering if anyone knows of anything that resembles a joint_view 
of a pair of maps.

    typedef mpl::int_<1> key1_;
    typedef mpl::int_<2> key2_;

    typedef pair pair1_;
    typedef pair pair2_;

     typedef map map1_;
     typedef map map2_;

     map1_ m1( make_pair(1) );
     map2_ m2( make_pair(2) );
     typedef joint_view<
         map1_,
         map2_
     > jv_;

     // not supposed to compile (?), yet it does:
     jv_ view(m1,m2);
     // but not this:
     // at_key(view)

     // I have no choice (?) but create a new map,
     // although view helps a bit for initializing it:
     typedef map<
         pair1_,
         pair2_
     > map3_;

     map3_ m3 = fusion::as_map(view);

     int n1 = fusion::at_key(m3);
     BOOST_ASSERT(n1 == 1);
     int n2 = fusion::at_key(m3);
     BOOST_ASSERT(n2 == 2);