Methods overloading with value and reference parameter types

Question

I have the following code :

class Calculator
    {
        public int Sum(int x, int y)
        {
            return x + y;
        }



        public int Sum(out int x, out int y)
        {
            x = y = 10;
            return x + y;
        }


    }

    class Program
    {
        static void Main(string[] args)
        {
            int x = 10, y = 20;
            Calculator calculator = new Calculator();

            Console.WriteLine ( calculator.Sum ( x , y ) );
            Console.WriteLine ( calculator.Sum ( out x , out y ) );

        }
    }

This code work well despite that methods signature are differenciated only be the out keyword.

But the following code didn't work :

class Calculator
    {

        public int Sum(ref int x, ref int y)
        {
            return x + y;
        }

        public int Sum(out int x, out int y)
        {
            x = y = 10;
            return x + y;
        }

    }


    class Program
    {
        static void Main(string[] args)
        {
            int x = 10, y = 20;
            Calculator calculator = new Calculator();

            Console.WriteLine ( calculator.Sum ( ref x , ref y ) );
            Console.WriteLine ( calculator.Sum ( out x , out y ) );

        }
    }

Why this code didn't work ? Are keywords like ref and out part of methods signatures?

Answer 1

out parameter modifier (C# Reference)

Although the ref and out keywords cause different run-time behavior, they are not considered part of the method signature at compile time. Therefore, methods cannot be overloaded if the only difference is that one method takes a ref argument and the other takes an out argument.

Also see: ref (C# Reference)

Members of a class can't have signatures that differ only by ref and out. A compiler error occurs if the only difference between two members of a type is that one of them has a ref parameter and the other has an out parameter.