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

er

20 Sep 2009 20 Sep '09

3:07 a.m.

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);

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Christopher Schmidt

20 Sep 20 Sep

9:55 a.m.

New subject: [fusion] is there anything resembling a joint_view of 2 maps?

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:

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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);

er

3:50 p.m.

New subject: [fusion] is there anything resembling a joint_view of 2 maps?

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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?

Christopher Schmidt

4:23 p.m.

New subject: [fusion] is there anything resembling a joint_view of 2 maps?

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_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. -Christopher er schrieb:

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I guess it wouldn't be a good idea for me to mix files from c++0x-port and boost.

er

22 Oct 22 Oct

9:34 p.m.

New subject: [fusion] is there anything resembling a joint_view of 2 maps?

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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>()); ???? } };

Joel de Guzman

21 Sep 21 Sep

12:42 a.m.

New subject: [fusion] is there anything resembling a joint_view of 2 maps?

er wrote:

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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

Christopher Schmidt

5:20 p.m.

New subject: [fusion] is there anything resembling a joint_view of 2 maps?

I certainly am. Once the review of my port is done, I will start working on it. -Christopher Joel de Guzman schrieb:

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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,

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