using System;

public class IncrementalSelection<T> where T : struct, IConvertible // reject all types other than enum
{
	public T selectedItem{ get; private set;}

	public IncrementalSelection(T initialSelection)
	{
	    if (!typeof(T).IsEnum)
	    {
      	   throw new ArgumentException("T must be an enumerated type");  // reject all types other than enum
        }
		selectedItem = initialSelection;
	}

	public void Increment()
	{
		selectedItem = (T)(object)(((int)(object)selectedItem)+1);
		if((int)(object)selectedItem >= Enum.GetNames(typeof(T)).Length)
		{
			selectedItem = (T)Enum.GetValues(typeof(T)).GetValue(0);
		}
	}
}

public class Program
{
	enum Focus {
		Narrow,
		Normal,
		Wide
	};

	public static void Main()
	{
		var focus = new IncrementalSelection<Focus>(Focus.Normal);

		System.Console.WriteLine(Enum.GetName(typeof(Focus), focus.selectedItem));
		focus.Increment();

		System.Console.WriteLine(Enum.GetName(typeof(Focus), focus.selectedItem));
		focus.Increment();

		System.Console.WriteLine(Enum.GetName(typeof(Focus), focus.selectedItem));
		focus.Increment();

		System.Console.WriteLine(Enum.GetName(typeof(Focus), focus.selectedItem));
		focus.Increment();
	}
}