I would have thought that one could do this? Yet, it doesn't seem to be the case. Why? Or am I doing something wrong?

#include<vector>
#include<initializer_list>
#include<iostream>

using namespace std;

void fn(std::initializer_list<int> i)
{
  for(int ivalue:i)
  {
    cout << ivalue << endl;
  }
}

int main()
{
  fn({1,2,3});
  fn(vector<int>{4,5,6})
  return 0;
}

demo