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

Subject: Re: [Boost-users] [fusion] is there anything resembling a joint_view of 2 maps?
From: Christopher Schmidt (mr.chr.schmidt_at_[hidden])
Date: 2009-09-20 05:55:41

The current implementation of views do not preserve the associative-ness 
of the underlying sequence(s). In your specific example, the joint_view 
is a plain forward sequence.

You could try my c++0x-port of Boost.Fusion. My implementation correctly 
preserves the category. You can find the code in the sandbox 
(https://svn.boost.org/trac/boost/browser/sandbox/SOC/2009/fusion).

-Christopher

er schrieb:
> 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<key1_,int> pair1_;
>    typedef pair<key2_,int> pair2_;
> 
>     typedef map<pair1_> map1_;
>     typedef map<pair2_> map2_;
> 
>     map1_ m1( make_pair<key1_>(1) );
>     map2_ m2( make_pair<key2_>(2) );
>     typedef joint_view<
>         map1_,
>         map2_
>     > jv_;
> 
>     // not supposed to compile (?), yet it does:
>     jv_ view(m1,m2);
>     // but not this:
>     // at_key<key1_>(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<key1_>(m3);
>     BOOST_ASSERT(n1 == 1);
>     int n2 = fusion::at_key<key2_>(m3);
>     BOOST_ASSERT(n2 == 2);