function param deduction

function_types.cpp

#include <tuple>
#include <iostream>
#include <typeinfo>

template<typename Ret>
struct function_type
{
};

template<typename Ret>
struct function_type<Ret ()>
{
  typedef Ret return_type;
  typedef std::tuple<> arg_types;
  static const size_t arity = 0;
};

template<typename Ret, typename Arg1>
struct function_type<Ret (Arg1)>
{
  typedef Ret return_type;
  typedef std::tuple<Arg1> arg_types;
  static const size_t arity = 1;
};

template<typename Ret, typename Arg1, typename Arg2>
struct function_type<Ret (Arg1, Arg2)>
{
  typedef Ret return_type;
  typedef std::tuple<Arg1, Arg2> arg_types;
  static const size_t arity = 2;
};



int main()
{
  std::cout << "return type: " << typeid(function_type<void ()>::return_type).name() << std::endl;
  typedef std::tuple_element<0, function_type<void (const int &)>::arg_types>::type argtype0;
  std::cout << "0th arg type: " << typeid(argtype0).name() << std::endl;
  std::cout << "0th arg type is ref: " << std::is_lvalue_reference<argtype0>::value << std::endl;
  std::cout << "0th arg type is const: " << std::is_reference<argtype0>::value << std::endl;
}