[Boost-users] [Phoenix] : Using phoenix with zip_iterator

Subject: [Boost-users] [Phoenix] : Using phoenix with zip_iterator
From: Manjunath Kudlur (keveman_at_[hidden])
Date: 2010-03-15 23:17:03

I have the following program where I make_zip_iterator on 2
vector<int>::iterator's and am trying to pass a Phoenix expression to
std::for_each on the iterator. I wrote a lazy version of tuple.get<N>
for that purpose. I get a compile error because the phoenix functor
only accepts references, whereas the tuple element seems to get passed
by value. What am I doing wrong?

Manjunath

#include <iostream>
#include <vector>
#include <algorithm>

#include <boost/iterator/zip_iterator.hpp>
#include <boost/tuple/tuple.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_statement.hpp>
#include <boost/spirit/include/phoenix_scope.hpp>
#include <boost/spirit/home/phoenix/function/function.hpp>

using namespace boost::phoenix;
using namespace boost::phoenix::arg_names;
using namespace boost::phoenix::local_names;
using namespace std;
namespace fusion = boost::fusion;

struct print_tuple {
  void operator()(const boost::tuple<int&, int&>& t) const {
    cout << t.get<0>() << " " << t.get<1>() << "\n";
  }
};

struct get0_ {
  template<typename Arg>
  struct result {
    typedef int type;
  };

  template<typename Arg>
  int operator()(Arg a1) const {
    return a1.get<0>();
  }
};

function<get0_> get0;

int main()
{
  vector<int> a(10), b(10);

  for(unsigned i=0, e=a.size(); i!=e; ++i) {
    a[i] = i;
    b[i] = i;
  }

  std::for_each(a.begin(), a.end(), cout << arg1);

  std::for_each(boost::make_zip_iterator(boost::make_tuple(a.begin(),
b.begin())),
                boost::make_zip_iterator(boost::make_tuple(a.end(),
b.end())), cout << get0(arg1));
}