Hello to everybody. Im using the great library Boost.Foreach and very happy with it, however currently I met some strange issue I want to show you. Im using custom wrappers to iterate over mapped values in std::map<> container. Here is the wrapper: template<typename CONT> struct Select2ndIt { CONT& cont; Select2ndIt(CONT& cont) : cont(cont) {} typedef typename CONT::mapped_type value_type; struct iterator : public std::iterator { typename CONT::iterator it; // typedef typename CONT::iterator::difference_type difference_type; typedef value_type* pointer; typedef value_type& reference; iterator(typename CONT::iterator it) : it(it) {} bool operator==(const iterator& other) const { return it == other.it; } bool operator!=(const iterator& other) const { return it != other.it; } iterator& operator++() { ++it; return *this; } iterator& operator++(int) { it++; return *this; } iterator& operator--() { --it; return *this; } iterator& operator--(int) { it--; return *this; } reference operator*() const { return it->second; } pointer operator->() const { return &it->second; } }; struct const_iterator : public std::iterator { typename CONT::const_iterator it; // typedef typename CONT::const_iterator::difference_type difference_type; typedef const value_type* pointer; typedef const value_type& reference; const_iterator(typename CONT::const_iterator it) : it(it) {} bool operator==(const const_iterator& other) const { return it == other.it; } bool operator!=(const const_iterator& other) const { return it != other.it; } const_iterator& operator++() { ++it; return *this; } const_iterator& operator++(int) { it++; return *this; } const_iterator& operator--() { --it; return *this; } const_iterator& operator--(int) { it--; return *this; } reference operator*() const { return it->second; } pointer operator->() const { return &it->second; } }; iterator begin() { return iterator(cont.begin()); } iterator end() { return iterator(cont.end()); } const_iterator begin() const { return const_iterator(cont.begin()); } const_iterator end() const { return const_iterator(cont.end()); } }; template<typename CONT> Select2ndIt<CONT> select2nd(CONT& cont) { return Select2ndIt<CONT>(cont); } And usage: std::map cont; BOOST_FOREACH(unsigned& value, alg::select2nd(cont)) value = 0; And MSVS 8.0 tells: error C2440: 'initializing' : cannot convert from 'const unsigned int' to 'unsigned int &' Without wrappers I can easily iterate as a non-const value: std::map cont; typedef std::pair value_type; BOOST_FOREACH(value_type& value, cont) value.second = 0; works great. I guess my wrappers very close to STL iterators (they even inherit from std::iterator), however some unwanted constness is appearing, so I afraid it is some issue with Boost.Foreach library. I hope for some help or advice about this problem. Thanks. Evgeny.