#include <string>
#include <iostream>

template<typename Ret>
Ret foo(const char *,int);
template<>
std::string foo<std::string>(const char *s,int) { return s; }
template<>
int         foo<int        >(const char *,int i) { return i; }


#include<tuple>

template<size_t num_args, typename ...T>
class Foo;
template<typename ...T>
class Foo<2,T...> : public std::tuple<T&&...>
{
public: 
        Foo(T&&... args) :
                std::tuple<T&&...>(std::forward<T>(args)...)
        {}
        template< typename Return >
        operator Return() { return foo<Return>(std::get<0>(*this), std::get<1>(*this)); }
};
template<typename ...T>
class Foo<3,T...> : std::tuple<T&&...>
{
public: 
        Foo(T&&... args) :
                std::tuple<T&&...>(std::forward<T>(args)...)
        {}
        template< typename Return >
        operator Return() { return foo<Return>(std::get<0>(*this), std::get<1>(*this), std::get<2>(*this)); }
};

template<typename ...T>
auto
auto_foo(T&&... args)
        // -> Foo<T&&...> // old, incorrect, code
        -> Foo< sizeof...(T), T&&...> // to count the arguments
{
        return              {std::forward<T>(args)...};
}




int main() {
        std::string s = auto_foo("hi",5); std::cout << s << std::endl;
        int         i = auto_foo("hi",5); std::cout << i << std::endl;
}