c++ - Overload operator>> for std::pair<int, int> -

i trying use boost::lexical_cast on std::pair<int, int>.

#include <iostream> #include <utility> #include <boost/lexical_cast.hpp>  namespace {   // when my_pair user defined type, program compiles   // , runs without problems.   // when declaring my_pair alias of std::pair<int, int>,   // fails compile    /*   struct my_pair   {       int first;       int second;   };   */    using my_pair = std::pair<int, int>;    std::istream& operator>>(std::istream& stream, my_pair& pair)   {     stream >> pair.first;     stream >> std::skipws;     stream >> pair.second;     return stream;   } }  int main() {   my::my_pair p = boost::lexical_cast<my::my_pair>("10 10");   std::cout << p.first << " " << p.second << std::endl;   return 0; } 

if understand right, in order make adl work, operator>> has in same namespace my_pair, std.

doing so, result in undefined behavior, because adding functions namespace std.

i avoid inheritance, in struct my_pair : std::pair<int, int>.

what solution problem?

i using clang++-3.6 on os x.

instead of adl-hooking on value stream, overload on stream (tagging in way):

int main() {     std::map<int, std::string> standback { { 42, "i'm gonna try" }, { 1729, "science" } };      streaming::tag_ostream out = std::cout;      (auto& entry : standback)         out << entry << "\n"; } 

this way, can adl-hook on namespace under control. can make tagging more generic (think auto out = streaming::tag(std::cout)).

now, simple implementation of like

namespace streaming {      template <typename t>     struct tag : std::reference_wrapper<t> {         using std::reference_wrapper<t>::reference_wrapper;     };      using tag_ostream = tag<std::ostream>;      template <typename t1, typename t2>     static inline tag_ostream operator<<(tag_ostream os, std::pair<t1, t2> const& p) {         os.get() << "std::pair{" << p.first << ", " << p.second  << "}";         return os;     }      template <typename other>     static inline tag_ostream operator<<(tag_ostream os, other const& o) {         os.get() << o;         return os;     } } 

see live on coliru, prints:

std::pair{42, i'm gonna try} std::pair{1729, science}