Must a reference type be initialized in constructor initialization list?

Question

As self-exercise, I have written this simple code:

#include 

int gIndex = 3;

template  class Array
{
public:
    explicit Ar         


        

Answer 1

Must any class-member reference type be initialized in the constructor initialization list?

Yes.

Is that related somehow to the fact that a reference type can never be reassigned?

Yes, plus the fact that there is no "null" or default construction for a reference. It is an alias for another object, and it has to be bound to it from the outset. You cannot do this (this is not inside a class definition):

int main()
{
  int& iref; // ERROR
  int i = 42;
  int& iref2 = i; // OK
}

because iref must alias something.