But what do I do about the reference type? I can't use std::pair<const KEY,VALUE>& because
Provided I understood correctly, would this be a possibility? #ifndef BOOST_MAP2_ZIP_FUNC #define BOOST_MAP2_ZIP_FUNC #include <boost/tuple/tuple.hpp> #include <boost/iterator/zip_iterator.hpp> #include <boost/iterator/transform_iterator.hpp> #include <boost/ref.hpp> #include <utility> namespace boost{ namespace map2{ template<typename Key,typename Value> struct zip_func { zip_func(){} typedef const boost::tuple< const Key&, Value& >& argument_type; typedef std::pair<Key,boost::reference_wrapper<Value> > result_type; result_type operator()(argument_type t) const { return result_type( boost::get<0>(t), boost::ref(boost::get<1>(t)) ); } }; template<typename ItK,typename ItV> struct iterator{ typedef boost::tuple< ItK, ItV > it_tuple_; typedef typename boost::zip_iterator<it_tuple_> zip_iter_; typedef typename boost::iterator_value<ItK>::type k_; typedef typename boost::iterator_value<ItV>::type v_; typedef zip_func<k_,v_> func_; typedef boost::transform_iterator<func_,zip_iter_> type; static type call(ItK it_k,ItV it_v){ return type(zip_iter_(it_tuple_(it_k,it_v)),func_()); } }; }// map2 }// boost #endif #include <vector> #include <iostream> #include <boost/assign/std/vector.hpp> #include <map2_iterator.hpp> int main (int argc, char * const argv[]) { typedef int key_; typedef int val_; typedef std::vector<key_> keys_; typedef std::vector<val_> vals_; using namespace boost::assign; keys_ keys; keys += 1,2,3; vals_ vals; vals += 1,2,3; typedef boost::range_iterator<keys_>::type it_k_; typedef boost::range_iterator<vals_>::type it_v_; typedef boost::map2::iterator<it_k_,it_v_> meta_map2_; typedef meta_map2_::type it_map_; it_map_ b_map = meta_map2_::call(boost::begin(keys),boost::begin(vals)); it_map_ e_map = meta_map2_::call(boost::end(keys),boost::end(vals)); int i = 1; while(b_map!=e_map){ BOOST_ASSERT(vals[i-1] == i); ++(b_map->second); BOOST_ASSERT(vals[i-1] == i+1); ++b_map; ++i; } return 0; }