-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Steven Watanabe Sent: Friday, August 03, 2012 7:40 PM To: boost@lists.boost.org Subject: Re: [boost] [type_erasure] Review started (July 18-27, 2012)
AMDG
Further to my enthusiastic welcome to print sequence example, I have extended this to other types, but come unstuck for std::map :-( I've created a map std::map<int, double> my_map; my_map.insert(std::make_pair(1, 9.9)); my_map.insert(std::make_pair(2, 8.8)); and made sure I can output the values using a forward iterator for (std::map<int, double>::iterator it = my_map.begin(); it != my_map.end(); ++it) { std::cout << *it << std::endl; } with an operator<< for pair (untidily in global namespace for the purpose of this example). template <typename K, typename T> std::ostream& operator<< (std::ostream& os, std::pair<K, T>& p) { /*! Output a pair of values. \details For example: "1.23 , 3.45". */ os << p.first << ", " << p.second; return os; } And I can echo the input as expected 1, 9.9000 2, 8.8000 but when I try to use the sequence printer p2.print(std::cout, my_map); the compiler (VC10) complains the there is no operator<< I:\boost-sandbox\type_erasure\boost/type_erasure/operators.hpp(422): error C2679: binary '<<' : no operator found which takes a right-hand operand of type 'const std::pair<_Ty1,_Ty2>' (or there is no acceptable conversion) with [ _Ty1=const int, _Ty2=double ] (I've tried several combinations of const or not, const int or int, and pair<K, T> and <K, T>& so I can't see that this is a const issue or ref issue). What am I doing wrong? Paul PS I'm not sure I understand the base_and_derived and concept_interface structs and how they are used. Some explanation would be useful for the novice. --- Paul A. Bristow, Prizet Farmhouse, Kendal LA8 8AB UK +44 1539 561830 07714330204 pbristow@hetp.u-net.com