C++ template that knows its argument's position

Question

I am new in c++ metaprogramming and few days ago I decided to write a template with variadic parameter pack, that knows in which position in parameter pack stands first int. More precisely I want to have a struct with name GetIntPos and with static constexpr int value which indicates the position of int in parameter pack starting with 1, and 0 if there is no int parameter type in parameter pack. For example

cout<<GetIntPos<long, char, int, long>::value; // must print 3
cout<<GetIntPos<int, int, long>::value; // must print 1

and

cout<<GetIntPos<long, long, char>::value; // must print 0;

How can it be done?

Answer 1

My recursive way

#include <iostream>
#include <type_traits>

template <std::size_t, typename ...>
struct GIP_helper
   : public std::integral_constant<std::size_t, 0u>
 { };

template <std::size_t N, typename T0, typename ... Ts>
struct GIP_helper<N, T0, Ts...>
   : public GIP_helper<N+1u, Ts...>
 { };

template <std::size_t N, typename ... Ts>
struct GIP_helper<N, int, Ts...>
   : public std::integral_constant<std::size_t, N>
 { };


template <typename... Ts>
struct GetIntPos : public GIP_helper<1u, Ts...>
 { };

int main()
 {
   std::cout << GetIntPos<long, char, int, long>::value << std::endl; 
   std::cout << GetIntPos<int, int, long>::value << std::endl;
   std::cout << GetIntPos<long, long, char>::value << std::endl;
 }

Works starting from C++11.