Why can't the elements of the list be ref?

Question

Answer 1

@명관 송 , based on my test, I reproduced your problem.

According to the Microsoft doc ref said, An argument that is passed to a ref or in parameter must be initialized before it is passed.

Therfore, we could use the following code to initialize the argument.

  public static void GetSuffleList<T>(ref List<T>_list)  
        {  
            for (int i = 0; i < _list.Count; i++)  
            {  
                Random random = new Random();  
                int rnd = random.Next(0, i);  
                T t1= _list[i];  
                T t2= _list[rnd];  
                Swap(ref t1 ,ref t2);  
  
            }  
        }  
   

Hope this coudl help you.

Best Regards,
Jack

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Answer 2

Pass by ref means you pass the address of the variable, rather than the address of the value. But indexing into an array is really method that return a value, not a variable.

As suggested above you could copy the indexed values to variable, but calling your swap would swap the values in variables not the list.