#217 – T? Is Equivalent to Nullable<T>

You can always use the form T?, rather than Nullable<T>, to declare a variable whose type is a nullable value type.  The type T can be any built-in or custom value type.

This means that you can use this syntax for your own custom enum or struct types.

For example, if you have the following custom types:

        public enum Mood
        {
            Crabby,
            Happy,
            Petulant,
            Elated
        }

        public struct Point3D
        {
            public float X, Y, Z;
            public string Name;
            public Point3D(float x, float y, float z, string name)
            {
                X = x;
                Y = y;
                Z = z;
                Name = name;
            }
        }

You can use the T? format as follows:

            Mood? myMood = null;
            Mood mood2 = myMood ?? Mood.Elated;

            Point3D? somePoint = null;
            Point3D defaultPoint = new Point3D(0.0f, 0.0f, 0.0f, "Origin");
            Point3D aPoint = somePoint ?? defaultPoint;