Hello all, I've encountered some behaviour of maps in both fusion and mpl that I did not expect, when inserting elements with the same key. Both libraries behave the same. To illustrate, I wrote the code below (full source at the end of this post), where I create a map with a single element an then insert an element with the same key (int_<1>). I expected the size<> of the resulting map to be 1. Instead, the size is 2. (all on msvc9 and gcc 4.1.2 (MinGW), boost 1.35 and svn_head) ----------------------------------- typedef pair< int_<1>, vector< int> > first_element; typedef pair< int_<1>, vector< int, int> > second_element; typedef map< first_element> first_map; typedef insert< first_map, second_element>::type second_map; // it prints "2", I expected "1". std::cout << size< second_map>::type() << std::endl; ----------------------------------- Generally, when I inspect the type of the resulting map after several inserts, I see that all inserted elements are still there. What is wrong with the above code? What should I do if I wanted the original entry to be replaced with the new one? Danny. ------source------- #include <iostream> #include #include #include #include #include #include #include #include #include #include #include #include #include <utility> // std::pair //#define USE_FUSION int main(int argc, char* argv[]) { #ifdef USE_FUSION using namespace boost::fusion::result_of; using std::pair; using boost::fusion::vector; using boost::fusion::map; #else using namespace boost::mpl; #endif using boost::mpl::int_; typedef pair< int_<1>, vector< int> > first_element; typedef pair< int_<1>, vector< int, int> > second_element; typedef map< first_element> first_map; typedef insert< first_map, end< first_map>::type, second_element>::type second_map; std::cout << size< second_map>::type() << std::endl; return 0; }