Hi! I'd like to use boost::tuple in a list-replacing multiindex and use the first entry in the tuple as key. The following fails to compile. Could you please provide a correction? #include <boost/tuple/tuple.hpp> #include <boost/multi_index_container.hpp> #include <boost/multi_index/sequenced_index.hpp> #include <boost/multi_index/key_extractors.hpp> namespace bm = ::boost::multi_index; class C { typedef boost::tuple<std::string, std::string> data_t; template <typename T> struct mutable_value { mutable_value(const T& t):t(t){} operator T&()const{return t;} private: mutable T t; }; typedef bm::multi_index_container <mutable_value<data_t>, bm::indexed_by <bm::sequenced<>, bm::ordered_unique <bm::mem_fun<data_t, std::string, &data_t::get<0> > > > > storage_t; storage_t storage_; }; int main() { C c; }