Common types in two TypeSets / Tuples

Question

I have two tuples -- TypeSets modeled as tuples, and thus guaranteed to contain each type at maximum once in their parameter packs, to be exact -- (say A = std::tuple and B = std::tuple), and I wish to obtain a typedef that corresponds to a tuple of types in the intersection of A and B (in this case, tuple_intersect::type = std::tuple). How do I go about this? JavaScript questions and answers, JavaScript questions pdf, JavaScript question bank, JavaScript questions and answers pdf, mcq on JavaScript pdf, JavaScript questions and solutions, JavaScript mcq Test , Interview JavaScript questions, JavaScript Questions for Interview, JavaScript MCQ (Multiple Choice Questions)

Answer 1

You can use the indices trick along with has_type (from here): #include #include // ############################################## // from https://stackoverflow.com/a/25958302/678093 template struct has_type; template struct has_type> : std::false_type {}; template struct has_type> : has_type> {}; template struct has_type> : std::true_type {}; // ############################################## template struct intersect { template static constexpr auto make_intersection(std::index_sequence ) { return std::tuple_cat( std::conditional_t< has_type< std::tuple_element_t, S2 >::value, std::tuple>, std::tuple<> >{}...); } using type = decltype(make_intersection(std::make_index_sequence::value>{})); }; struct T1{}; struct T2{}; struct T3{}; using A = std::tuple; using B = std::tuple; int main() { static_assert(std::is_same, intersect::type>::value, ""); } live example