[Boost-users] [mpl] Problem comparing iterators

From: Küppers, Ben (ben.kuppers_at_[hidden])
Date: 2007-01-18 09:22:20

Gents,

For illustration purposes I created the following code that iterates through a sequence and accumulates the distances between the current iterator and the beginning of the sequence. Somehow this code works for normal ranges (range1 and range2) but fails to compile for joint_view range3 (80-plus errors). Changing the call to distance to compare between begin and end or between _2 and _2 (self) works. I am at a loss here. Can someone point out what I am doing wrong?

Thanks
Ben

#include <iostream>

#include <boost/mpl/arithmetic.hpp>
#include <boost/mpl/begin.hpp>
#include <boost/mpl/distance.hpp>
#include <boost/mpl/for_each.hpp>
#include <boost/mpl/iter_fold.hpp>
#include <boost/mpl/joint_view.hpp>
#include <boost/mpl/plus.hpp>
#include <boost/mpl/push_back.hpp>
#include <boost/mpl/range_c.hpp>
#include <boost/mpl/vector_c.hpp>

namespace mpl = boost::mpl;

template< class _Sequence >
struct distances {
   typedef typename mpl::iter_fold<
      _Sequence,
      mpl::long_< 0 >,
      mpl::plus<
         mpl::_1,
         mpl::distance<
            typename mpl::begin< _Sequence >::type,
//            typename mpl::end< _Sequence >::type
//            mpl::_2,
            mpl::_2
         >
      >
   >::type type;
};

int main( int argc, char* argv[] )
{
   typedef mpl::range_c< char, 'a', 'd' >::type range1;
   typedef mpl::range_c< char, 'm', 'q' >::type range2;
   typedef mpl::joint_view< range1, range2 >::type range3;
   typedef distances< range3 >::type type1;

   std::cout << type1();

   std::cout << std::endl;

   return 0;
}

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