[Boost-users] [type_traits][function_traits] generic way of obtaining argument of *both* a function and function object

Subject: [Boost-users] [type_traits][function_traits] generic way of obtaining argument of *both* a function and function object
From: alfC (alfredo.correa_at_[hidden])
Date: 2011-09-06 17:48:36

Hi,

 Is there a uniform way to obtain the argument type of function object and 
of a function at the same time.

For example:

double fun(int a){ return ... ;}
struct A{
  double operator()(int a){ return ...;}
  typedef int argument_type; // or something like this (if needed)
};

template<class F> print_argument_type(F f){
   std::cout << typeid(
          argument_of<F>::type // or something like this ?? 
   ).name() << std::endl;
}

A a;
print_argument(fun); //should print  "int"
print_argument(a); //should print  "int"

Of course I am asking for something that at least works on objects in which 
operator() is not overloaded. 
For functions we have function_traits< ... >::arg1_type (and other MPL 
variants) but I can not find a generic solution that also works for objects.

In other words I need something like boost/std::result_of but for the 
argument type; if this is not possible in general because of language 
limitations (e.g. because operator() can be overloaded) I am willing to 
accept any convention from out there that works both for functions and 
funciton objects. Just wanted to know what boost can say about this problem.

Maybe something that looks into the arguments of the member-function 
A::operator() via type_traits in case A is a class?

Thanks,
Alfredo