#585 – Optional Parameters Must Come Last

If you define a method that includes optional parameters, they must come after any required parameters.  This means that your options for required vs. optional parameters are:

• No parameters at all
• 1 or more required parameters (no default values)
• 1 or more optional parameters (with default values)
• 1 or more required parameters, followed by 1 or more optional parameters

        static void NoParams() { }
        static void RequiredOnly(int x, int y) { }
        static void OptionalOnly(int x = 5, int y = 10) { }
        static void RequiredAndOptional(int x, int y, int a = 1, int b = 2) { }

        static void Main()
        {
            NoParams();
            RequiredOnly(5, 10);

            OptionalOnly();
            OptionalOnly(1);
            OptionalOnly(1, 2);

            RequiredAndOptional(1, 1);
            RequiredAndOptional(1, 2, 3);
            RequiredAndOptional(1, 2, 3, 4);
        }