c++ - Get the type of a function parameter with boost::hana -

i know how type of function's parameter old way, wondering if there nice new way hana? example, want this:

struct foo {     int func(float); };  auto getfunctype(auto t) -> declval<decltype(t)::type>()::func(type?) {} getfuntype(type_c<foo>); // should equal type_c<float> or similar 

how type here?

edit 6/21/2016 - minor changes match current version of library (0.4).

i'm author of callabletraits, library mentioned above @ildjarn (although not yet included in boost). arg_at_t metafunction best way know parameter type member function, function, function pointer, function reference, or function object/lambda.

please keep in mind library undergoing significant changes, , linked documentation outdated (i.e. use @ own risk). if use it, recommend cloning develop branch. feature seeking, api not change.

for member function pointers, arg_at_t<0, mem_fn_ptr> aliases equivalent of decltype(*this), account implicit this pointer. so, case, this:

#include <type_traits> #include <callable_traits/arg_at.hpp>  struct foo {     int func(float); };  using func_param = callable_traits::arg_at_t<1, decltype(&foo::func)>;  static_assert(std::is_same<func_param, float>::value, "");  int main(){} 

then, can put boost::hana::type or whatever use case requires.

live example