#include <utility>
#include <iostream>

namespace
{
    template <typename T>
    auto priority_helper(T&& t, int, int, int) -> decltype(t.first())
    {
      return t.first();
    }

    template <typename T>
    auto priority_helper(T&& t, int, int, long) -> decltype(t.second())
    {
      return t.second();
    }

    template <typename T>
    auto priority_helper(T&& t, int, long, long) -> decltype(t.third())
    {
      return t.third();
    }

    template <typename T>
    int priority_helper(T&&, long, long, long)
    {
      return 4;
    }
}

template <typename T>
auto get_priority(T&& t)
{
  return priority_helper(std::forward<T>(t), 0, 0, 0);
}

struct X
{
  int first() const { return 1; }
};

struct Y
{
  int second() const { return 2; }
};

struct Z
{
  int third() const { return 3; }
};

struct XY
{
  int first() const { return 1; }
  int second() const { return 2; }
};

struct XZ
{
  int first() const { return 1; }
  int third() const { return 3; }
};

struct YZ
{
  int second() const { return 2; }
  int third() const { return 3; }
};

struct XYZ
{
  int first() const { return 1; }
  int second() const { return 2; }
  int third() const { return 3; }
};

/*
  Correct output should be:
1
2
3
1
1
2
1
4
 */
int main()
{
  using std::cout;
  using std::endl;
  
  cout << get_priority(X{}) << endl
       << get_priority(Y{}) << endl
       << get_priority(Z{}) << endl
       << get_priority(XY{}) << endl
       << get_priority(XZ{}) << endl
       << get_priority(YZ{}) << endl
       << get_priority(XYZ{}) << endl
       << get_priority(5) << endl;
}