Hi, I have currently template <typename Key, typename Value> std::vector<Key> keys(const std::map<Key, Value> &m) { ... } I'd like to write an overload that works also with the indices interface of multi_index_container. Suppose I have a multi_index_container with ordered unique indexes tagged "by_id" and "by_name". struct by_id {}; struct by_name {}; using BMI = multi_index::multi_index_container<Value, multi_index::indexed_by< multi_index::ordered_unique<by_id, multi_index::key<&Value::id>>, multi_index::ordered_unique<by_name, multi_index::key<&Value::name>>
;
BMI bmi; auto k = keys(bmi.get<by_name>()); Based on the documentation, I tried template< typename Tag,typename Value,typename IndexSpecifierList,typename Allocator > auto keys(const typename multi_index::index< multi_index::multi_index_container<Value,IndexSpecifierList,Allocator>,Tag>::type& m) { typedef decltype(c.key_extractor()(*c.begin())) key_type; // A better definition would be welcome std::vector<key_type> result; result.reserve(c.size()); for (const auto &elem : c) { result.push_back(c.key_extractor()(elem)); } return result; } But the overload resolution fails. What should be the interface of keys in order to support indices interface of multi_index_container? Thank you, Christophe B