[Home]CPPTM Answers - Exercise 7-0

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 // (by Ariel Badichi)
 #include <boost/static_assert.hpp>
 #include <boost/mpl/iterator_tags.hpp>
 #include <boost/mpl/deref.hpp>
 #include <boost/mpl/transform.hpp>
 #include <boost/mpl/next.hpp>
 #include <boost/mpl/iterator_range.hpp>
 #include <boost/mpl/begin.hpp>
 #include <boost/mpl/end.hpp>
 #include <boost/mpl/transform_view.hpp>
 #include <boost/mpl/placeholders.hpp>
 #include <boost/mpl/vector_c.hpp>
 #include <boost/mpl/vector.hpp>
 #include <boost/mpl/unpack_args.hpp>
 #include <boost/mpl/plus.hpp>
 #include <boost/mpl/equal.hpp>

 namespace mpl = boost::mpl;
 using namespace boost::mpl::placeholders;

 template<typename IteratorSeq?>
 struct zip_iterator
 {
     typedef mpl::forward_iterator_tag category;

     typedef IteratorSeq? base;

     typedef typename mpl::transform<
         IteratorSeq?,
         mpl::deref<_1>
     >::type type;
 };

 namespace boost
 {
     namespace mpl
     {
         template<typename IteratorSeq?>
         struct next< ::zip_iterator<IteratorSeq?> >
         {
             typedef ::zip_iterator<
                 typename transform<
                     IteratorSeq?,
                     next<_1>
                 >::type
             > type;
         };
     }
 }

 // I use mpl::transform instead of mpl::transform_view written in the book.

 template<typename Sequences>
 struct zip_view
     : mpl::iterator_range<
           zip_iterator<
               typename mpl::transform<
                   Sequences, mpl::begin<_1>
               >::type
           >,
           zip_iterator<
               typename mpl::transform<
                   Sequences, mpl::end<_1>
               >::type
           >
       >
 {
 };

 int main()
 {
     typedef mpl::vector3_c<int, 1, 2, 3> v1;
     typedef mpl::vector3_c<int, 4, 5, 6> v2;
     typedef mpl::vector3_c<int, 7, 8, 9> v3;
     typedef mpl::vector3<v1, v2, v3> vecs;

     typedef mpl::transform_view<
         zip_view<vecs>, mpl::unpack_args<mpl::plus<_, _, _> >
     > view;

     typedef mpl::vector_c<int, 12, 15, 18> expected;
     BOOST_STATIC_ASSERT((mpl::equal<expected, view>::type::value));
 }


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Last edited March 27, 2005 11:52 am (diff)
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