c++ - Handle partial type with Boost Hana -

what call partial type here that:

template < template <typename ...> typename skeleton,            template <typename ...> typename wrappertype,            typename ... pölicies > struct metastorage {    template < typename ... ts >   struct with_type {      using type = skeleton<wrappertype<ts...>, policies...>;   }; };  using partialtype = metastorage<sk, wt, p1, p2, p3>; using finaltype = partialtype::with_type<t1, t2>; 

i don't think fits hana philosophy , it's not readable if want split type more this.

so efficient way of doing boost hana?

edit :

by mean, way allow user create final type in several steps. can use partial type generate every final type. usual syntax , hana::type.

with boost.hana can lift types values hana::type , same templates using hana::template_. can following:

#include <boost/hana.hpp>  namespace hana = boost::hana;   template <typename ...x> struct skeleton_t { }; constexpr auto skeleton = hana::template_<skeleton_t>; template <typename ...x> struct wrapper_t { }; constexpr auto wrapper = hana::template_<wrapper_t>; template <int i> struct policy_t { }; template <int i> constexpr auto policy = hana::type_c<policy_t<i>>; template <int i> struct foo_t { }; template <int i> constexpr auto foo = hana::type_c<foo_t<i>>;  int main() {   auto meta_storage = [](auto s, auto w, auto ...policies) {     return [=](auto ...ts) {       return s(w(ts...), policies...);     };   };    auto partial = meta_storage(skeleton, wrapper, policy<1>, policy<2>);    auto final_ = partial(foo<1>, foo<2>);    skeleton_t<wrapper_t<foo_t<1>, foo_t<2>>, policy_t<1>, policy_t<2>> check     = typename decltype(final_)::type{}; } 

personally prefer not bother hana::template_ in cases can use function. use macro create tag type along corresponding hana::type value reduce of setup see above main function.