[fusion] is there anything resembling a joint_view of 2 maps?
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);
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);
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
Thank you. I guess it wouldn't be a good idea for me to mix files from c++0x-port and boost. To those who support fusion: would it be wise to place a feature request for this, then?
My code is pretty much backwards compatible - there have not been any striking semantic changes and all testcases pass on gcc 3.4/4.4 and vc 9. Unfortunately I have not had the time to put the code up for review yet. I am pretty positive that the code is trunk-ready though, and I will try to post a report on my work within the next days. Either way, for now you can workaround your issue by providing your own extension implementations for fusion::extension::category_of_impl<fusion::joint_view_tag>, fusion::extension::has_key_impl<fusion::joint_view_tag> and fusion::extension::at_key_impl<fusion::joint_view_tag>, or, even better, wrap the joint_view up in another view which implements both (forward and associative) extension backends. -Christopher er schrieb:
I guess it wouldn't be a good idea for me to mix files from c++0x-port and boost.
Either way, for now you can workaround your issue by providing your own extension implementations for fusion::extension::category_of_impl<fusion::joint_view_tag>, fusion::extension::has_key_impl<fusion::joint_view_tag> and fusion::extension::at_key_impl<fusion::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<typename Seq1,typename Seq2,typename Key> struct at_key_impl<joint_view_tag>::apply< joint_view<Seq1,Seq2>,Key > { typedef joint_view<Seq1,Seq2> jv_; typedef fusion::result_of::has_key<Seq1,Key> has_key1_; typedef typename mpl::if_< has_key1_, Seq1, Seq2 >::type seq_; typedef typename result_of::at_key<seq_,Key>::type type; static type call(jv_& m) { // return m.at_impl(mpl::identity<Key>()); ???? } };
er wrote:
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
Thank you.
I guess it wouldn't be a good idea for me to mix files from c++0x-port and boost.
To those who support fusion: would it be wise to place a feature request for this, then?
Yes, please. Christopher, would you be interested to port to current fusion? That would provide a seamless integration from the current code to the future 0x code. Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net http://tinyurl.com/facebook-jdg
I certainly am. Once the review of my port is done, I will start working on it. -Christopher Joel de Guzman schrieb:
Yes, please. Christopher, would you be interested to port to current fusion? That would provide a seamless integration from the current code to the future 0x code.
Regards,
participants (3)
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Christopher Schmidt -
er -
Joel de Guzman