binary mpl::transform fails to compile with fusion::vector
I am hoping someone can point me the in right direction regarding this code snippit failing to compile. My suspicion is that it is a header problem but any help would be appreciated. In short, I seem to be missing why the binary form of mpl::transform won't work with fusion::vector. (unary form works just fine). The code below just attempts to make a std::pair<> from the contents of two sequences (this is just an example to illustrate the transform problem). If the two sequences are mpl::vectors, everything is fine. If they are fusion::vectors then 'lots of errors'. I'm fairly new to both mpl and fusion so I am not ruling out the fact that I have done something stupid. Thanks in advance, Mike See code below. #include <boost/mpl/transform.hpp> #include <boost/mpl/vector.hpp> #include <boost/fusion/include/mpl.hpp> #include <boost/fusion/container/vector.hpp> #include <utility> using namespace boost; struct my_make_pair { template<typename T1, typename T2> struct apply { typedef std::pair<T1,T2> type; }; }; int main(int argc, char *argv[]) { #if 0 typedef mpl::vector<int,long> seq1; typedef mpl::vector<float,double> seq2; typedef mpl::vector<std::pair<int,float>,std::pair<long,double> > pairs; typedef mpl::transform<seq1,seq2,my_make_pair>::type result; BOOST_MPL_ASSERT(( equal<result,pairs> )); #endif typedef fusion::vector<int,long> seq1; typedef fusion::vector<float,double> seq2; typedef fusion::vector<std::pair<int,float>,std::pair<long,double> > pairs; typedef mpl::transform<seq1,seq2,my_make_pair>::type result; BOOST_MPL_ASSERT(( equal<result,pairs> )); return 0; }
Mike Tegtmeyer wrote:
I am hoping someone can point me the in right direction regarding this code snippit failing to compile. My suspicion is that it is a header problem but any help would be appreciated.
In short, I seem to be missing why the binary form of mpl::transform won't work with fusion::vector. (unary form works just fine).
The code below just attempts to make a std::pair<> from the contents of two sequences (this is just an example to illustrate the transform problem). If the two sequences are mpl::vectors, everything is fine. If they are fusion::vectors then 'lots of errors'.
I'm fairly new to both mpl and fusion so I am not ruling out the fact that I have done something stupid.
Trying the code, it seems mpl::(binary)transform is looking for Seq::tag which is not a requirement for MPL::Forward Sequence which mpl::transform requires (http://tinyurl.com/l6kcb4). fusion::vector adheres fully to an MPL::Forward Sequence. I'm guessing this is an MPL problem, but I may be wrong, so I'll leave it to the better hands of Aleksey. Aleksey, can you help? Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net
On Wed, 17 Jun 2009 12:07:33 -0500, Joel de Guzman <djowel@gmail.com> wrote:
Mike Tegtmeyer wrote:
I am hoping someone can point me the in right direction regarding this code snippit failing to compile. My suspicion is that it is a header problem but any help would be appreciated. In short, I seem to be missing why the binary form of mpl::transform won't work with fusion::vector. (unary form works just fine). The code below just attempts to make a std::pair<> from the contents of two sequences (this is just an example to illustrate the transform problem). If the two sequences are mpl::vectors, everything is fine. If they are fusion::vectors then 'lots of errors'. I'm fairly new to both mpl and fusion so I am not ruling out the fact that I have done something stupid.
Trying the code, it seems mpl::(binary)transform is looking for Seq::tag which is not a requirement for MPL::Forward Sequence which mpl::transform requires (http://tinyurl.com/l6kcb4). fusion::vector adheres fully to an MPL::Forward Sequence.
No, the error is caused by the following code in MPL's pair_view (which is the underlying implementation mechanism for the binary transform): typedef typename min< typename iterator_category<iter1_>::type , typename iterator_category<iter2_>::type >::type category_; That is, as per iterator_category's requirements [1], pair_view assumes that the iterator_category's result would be model of MPL's Integral Constant, which does not seem to be the case with Fusion categories. [1] http://www.boost.org/doc/libs/1_39_0/libs/mpl/doc/refmanual/iterator-categor... HTH, -- Aleksey Gurtovoy MetaCommunications Engineering
Aleksey Gurtovoy wrote:
No, the error is caused by the following code in MPL's pair_view (which is the underlying implementation mechanism for the binary transform):
typedef typename min< typename iterator_category<iter1_>::type , typename iterator_category<iter2_>::type >::type category_;
That is, as per iterator_category's requirements [1], pair_view assumes that the iterator_category's result would be model of MPL's Integral Constant, which does not seem to be the case with Fusion categories.
[1] http://www.boost.org/doc/libs/1_39_0/libs/mpl/doc/refmanual/iterator-categor...
I see. It's a fusion bug then. I'll see what I can do. In the meantime, may I request the OP to add a trac ticket entry for this? Thank you, Aleksey! Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net
Done. Ticket #3204 Thanks for the help. Mike On Mon, 22 Jun 2009, Joel de Guzman wrote:
Aleksey Gurtovoy wrote:
No, the error is caused by the following code in MPL's pair_view (which is the underlying implementation mechanism for the binary transform):
typedef typename min< typename iterator_category<iter1_>::type , typename iterator_category<iter2_>::type >::type category_;
That is, as per iterator_category's requirements [1], pair_view assumes that the iterator_category's result would be model of MPL's Integral Constant, which does not seem to be the case with Fusion categories.
[1] http://www.boost.org/doc/libs/1_39_0/libs/mpl/doc/refmanual/iterator-categor...
I see. It's a fusion bug then. I'll see what I can do. In the meantime, may I request the OP to add a trac ticket entry for this?
Thank you, Aleksey!
Regards, -- Joel de Guzman http://www.boostpro.com http://spirit.sf.net
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participants (3)
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Aleksey Gurtovoy -
Joel de Guzman -
Mike Tegtmeyer