template<typename T1, typename T2>
std::ostream &operator<<(std::ostream &stream, const std::map<T1, T2>& map)
{
    for (typename std::map<T1, T2>::const_iterator it = map.begin();
         it != map.end();
         ++it)
    {
        stream << (*it).first << " --> " << (*it).second << std::endl;
    }
    return stream;
}