[Boost-users] [Iterator] zip iterator with std::tuple or std::pair

Subject: [Boost-users] [Iterator] zip iterator with std::tuple or std::pair
From: Matthias Wohlgemuth (mail_at_[hidden])
Date: 2017-03-23 13:30:39

Hello,

as far as I understand the zip_iterator is compatible also with STL 
tuple and pair.
However, when I try to create a zip_iterator with std::pair it fails to 
compile.

Here, a simple test code:

#include <vector>
#include <utility>
#include <boost/iterator/zip_iterator.hpp>
int main () {
   std::vector<int> v(4);
   boost::make_zip_iterator(std::make_pair(v.begin(), v.begin()));
   return 0;
}

compiled with gcc 4.9.2 and boost 1.62 returns me (tested also with 
1.63):

In file included from 
/software/boost-1.62/include/boost/iterator/zip_iterator.hpp:26:0,
                  from test.cpp:3:
/software/boost-1.62/include/boost/mpl/at.hpp: In instantiation of 
‘struct boost::mpl::at_c<std::pair<__gnu_cxx::__normal_iterator<int*, 
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int> 
 > >, 0l>’:
/software/boost-1.62/include/boost/iterator/zip_iterator.hpp:180:17:   
required from ‘struct 
boost::iterators::detail::zip_iterator_base<std::pair<__gnu_cxx::__normal_iterator<int*, 
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int> 
 > > >’
/software/boost-1.62/include/boost/iterator/zip_iterator.hpp:237:9:   
required from ‘class 
boost::iterators::zip_iterator<std::pair<__gnu_cxx::__normal_iterator<int*, 
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int> 
 > > >’
test.cpp:8:64:   required from here
/software/boost-1.62/include/boost/mpl/at.hpp:42:8: error: no class 
template named ‘apply’ in ‘struct 
boost::mpl::at_impl<boost::mpl::non_sequence_tag>’
  struct at_c
         ^
In file included from test.cpp:3:0:
/software/boost-1.62/include/boost/iterator/zip_iterator.hpp: In 
instantiation of ‘struct 
boost::iterators::detail::zip_iterator_base<std::pair<__gnu_cxx::__normal_iterator<int*, 
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int> 
 > > >’:
/software/boost-1.62/include/boost/iterator/zip_iterator.hpp:237:9:   
required from ‘class 
boost::iterators::zip_iterator<std::pair<__gnu_cxx::__normal_iterator<int*, 
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int> 
 > > >’
test.cpp:8:64:   required from here
/software/boost-1.62/include/boost/iterator/zip_iterator.hpp:180:17: 
error: no type named ‘type’ in ‘struct 
boost::mpl::at_c<std::pair<__gnu_cxx::__normal_iterator<int*, 
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int> 
 > >, 0l>’
          >::type difference_type;
                  ^
/software/boost-1.62/include/boost/iterator/zip_iterator.hpp:198:11: 
error: no type named ‘type’ in ‘struct 
boost::mpl::at_c<std::pair<__gnu_cxx::__normal_iterator<int*, 
std::vector<int> >, __gnu_cxx::__normal_iterator<int*, std::vector<int> 
 > >, 0l>’
          > type;

I get a similar results for std::tuple compiled c++11 enabled gcc.

I did not find any solution, except a 3 year old patch, which is said to 
be applied to the boost::iterator library.

Any suggestions?

Best regards,

Matthias