using System;

namespace DemoTypes
{
    struct Point
    {
        public int X, Y;

        public Point(int X, int Y)
        {
            this.X = Y;
            this.Y = Y;
        }
    }

    static class NullableDemo
    {
        public static void DoDemo()
        {
            Console.WriteLine("\nNullableDemo");
            Console.WriteLine("------------------------------------------------------");

            // To declare a nullable variable, append ? to value-type name.
            int? myNullableInt;         // Nullable primitive.
            Point? myNullablePoint;     // Nullable struct.
            DayOfWeek? myNullableDow;   // Nullable enum.

            // Alternative syntax.
            //   Nullable<int> myNullableInt2;       
            //   Nullable<Point> myNullablePoint2;   
            //   Nullable<DayOfWeek> myNullableDow2; 

            // You can assign null to any nullable-type variable.
            myNullableInt = null;       // Converts null to int?
            myNullablePoint = null;     // Converts null to Point?
            myNullableDow = null;       // Converts null to DayOfWeek?

            // .NET allows implicit conversion from T to T?
            myNullableInt = 10;                     // int to int?
            myNullablePoint = new Point(10, 20);    // Point to Point?
            myNullableDow = DayOfWeek.Friday;       // DayOfWeek to DayOfWeek?

            DisplayValues(myNullableInt, myNullablePoint, myNullableDow);
        }

        private static void DisplayValues(int? myNullableInt, Point? myNullablePoint, DayOfWeek? myNullableDow)
        {
            // Nullable types provide the HasValue and Value properties.
            if (myNullablePoint.HasValue)    
            {
                Point p = myNullablePoint.Value;
                Console.WriteLine("X coordinate: " + p.X);
                Console.WriteLine("Y coordinate: " + p.Y);
            }
            else
            {
                Console.WriteLine("No Point value at the moment");
            }

            if (myNullableInt.HasValue)
            {
                Console.WriteLine("Integer value: " + myNullableInt.Value);
            }
            else
            {
                Console.WriteLine("No integer value at the moment");
            }

            if (myNullableDow.HasValue)
            {
                Console.WriteLine("DayOfWeek value: " + myNullableDow.Value);
            }
            else
            {
                Console.WriteLine("No DayOfWeek value at the moment");
            }
        }
    }
}