gistfile1.cpp

template <typename T>
struct f_pair { T x; T y; };

template <typename T>
inline f_pair<T> make_square_pair(T x)
{
    return f_pair<T>{ x, x * x };
}

template <typename T>
inline T get_y(const f_pair<T>& p)
{
    return p.y;
}

#include <iostream>
#include <typeinfo>

template <typename T>
void display(T x)
{
    T y = get_y(make_square_pair(x));
    std::cout << y << " -> "<< (typeid(y).name()) << "\n";
}

...

display(2);                  //4 -> int
display(2.71828);            //7.38905 -> double
display(std::string("...")); //...... -> class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >