#include <tuple>

template<class T>
struct callable_trait
{};

template<class R, class... Args>
struct callable_trait<R(Args...)>
{
    using return_type    = R;
    using argument_types = std::tuple<Args...>;
};

template<auto callable>
using return_type = typename callable_trait<decltype(callable)>::return_type;

void f();
void g(return_type<f>);

error: no type named 'return_type' in 'callable_trait<void (*)()>'
using return_type = typename callable_trait<decltype(callable)>::return_type;
^~~~~

auto lambda= [](){};
void h(return_type<lambda>);

error: a non-type template parameter cannot have type '(lambda at <source>:19:14)'
void h(return_type<lambda>);
                   ^