Hana does not provide a way to merge two maps out of the box, although that would be very useful. I added a feature request at [1]. For now, you can use `fold_left` with `insert` to insert each element of the #include <boost/hana.hpp> #include <string> namespace hana = boost::hana; using namespace hana::literals; constexpr auto m1 = hana::make_map( hana::make_pair("key1"_s, hana::type_c<std::string>), hana::make_pair("key2"_s, hana::type_c<std::string>) ); constexpr auto m2 = hana::make_map( hana::make_pair("key3"_s, hana::type_c<std::string>), hana::make_pair("key4"_s, hana::type_c<std::string>), hana::make_pair("key5"_s, hana::type_c<std::string>) ); constexpr auto result = hana::fold_left(m1, m2, hana::insert); constexpr auto expected = hana::make_map( hana::make_pair("key1"_s, hana::type_c<std::string>), hana::make_pair("key2"_s, hana::type_c<std::string>), hana::make_pair("key3"_s, hana::type_c<std::string>), hana::make_pair("key4"_s, hana::type_c<std::string>), hana::make_pair("key5"_s, hana::type_c<std::string>) ); static_assert(result == expected, ""); int main() { } Also, while posting on this list is OK, please note that the preferred way to ask Hana-related questions is on StackOverflow with the [boost-hana] tag, as documented at [2]. This allows everybody to benefit from questions and answers, and I am registered to the tag so there's no chance that I miss your question as on this list. Regards, Louis [1]: https://github.com/boostorg/hana/issues/299 [2]: http://boostorg.github.io/hana/#tutorial-support -- View this message in context: http://boost.2283326.n4.nabble.com/Boost-Hana-how-to-merge-two-or-more-maps-... Sent from the Boost - Users mailing list archive at Nabble.com.