test.C

#include <iostream>
#include <vector>

template <typename T>
class ref_wrapper
{
public:
  ref_wrapper() = delete;
  ref_wrapper(T & obj) { ptr = &obj; }
  ref_wrapper(const ref_wrapper<T> & ref) { ptr = ref.ptr; }

  T & operator =(T value) { *ptr = value; return *ptr; }
private:
  T * ptr;
};


std::pair<unsigned int, ref_wrapper<int>>
getPair(std::vector<int> & vec, unsigned int index)
{
  // return std::make_pair(index, ref_wrapper<int>(vec[index]));
  return std::pair<unsigned int, ref_wrapper<int>>(index, ref_wrapper<int>(vec[index]));
}

int main()
{
  std::vector<int> test = { 1, 2, 3, 4 };

  for (auto i: test)
    std::cout << i << ' ';
  std::cout << '\n';

  auto access = getPair(test, 2);
  access.second = 22;

  auto wrap = ref_wrapper<int>(test[3]);
  wrap = 7;

  for (auto i: test)
    std::cout << i << ' ';
  std::cout << '\n';

  return 0;
}