How to add methods to an enum in C#

The problem

In C#, enums are simple value types which just contain a bunch of constants. No other type of member can be included.

Given that C# was influenced by C and C++, this is no surprise as enums in those languages only contain constants as well. However, Java allows enums to include methods so how can we do something similar in C#? 

The solution

The answer is to use extension methods which were introduced in C# 3.0.

Here's an example where we (effectively) add some methods to a Colors enum.

using System;

public enum Colors

{

    White,

    Red,

    Blue,

    Green

}

// extension methods for the Colors enum

public static class ColorsExtensions

{

    public static bool IsWhite(this Colors c)

    {

        return c == Colors.White;

    }

    public static bool IsRedOrBlue(this Colors c)

    {

        return c == Colors.Red || c == Colors.Blue;

    }

}

class Test

{

    static void Main()

    {

        Colors c = Colors.Red;

        Console.WriteLine(c.IsWhite()); // False

        Console.WriteLine(c.IsRedOrBlue());  // True

        Console.ReadKey();

    }

}