How to add extension methods to Enums

Question

I have this Enum code:

enum Duration { Day, Week, Month };

Can I add a extension methods for this Enum?

Answer 1

You can also add an extension method to the Enum type rather than an instance of the Enum:

/// 
 Enum Extension Methods 
///  type of Enum 
public class Enum where T : struct, IConvertible
{
    public static int Count
    {
        get
        {
            if (!typeof(T).IsEnum)
                throw new ArgumentException("T must be an enumerated type");

            return Enum.GetNames(typeof(T)).Length;
        }
    }
}

You can invoke the extension method above by doing:

var result = Enum.Count;

It's not a true extension method. It only works because Enum<> is a different type than System.Enum.