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

User · Answer

we have just made an enum extension for c# https://github.com/simonmau/enum_ext

It's just a implementation for the typesafeenum, but it works great so we made a package to share - have fun with it

public sealed class Weekday : TypeSafeNameEnum<Weekday, int>
{
    public static readonly Weekday Monday = new Weekday(1, "--Monday--");
    public static readonly Weekday Tuesday = new Weekday(2, "--Tuesday--");
    public static readonly Weekday Wednesday = new Weekday(3, "--Wednesday--");
    ....

    private Weekday(int id, string name) : base(id, name)
    {
    }

    public string AppendName(string input)
    {
        return $"{Name} {input}";
    }
}

I know the example is kind of useless, but you get the idea ;)

User · Answer

See MSDN   public static class Extensions     public static string SomeMethod this Duration enumValue            Do something here     return enumValue ToString  D

User · Answer

A Simple workaround   public static class EnumExtensions       public static int ToInt this Enum payLoad             return   int     IConvertible   payLoad            int num   YourEnum AItem ToInt    Console WriteLine  num      num

User · Answer

According to this site   Extension methods provide a way to write methods for existing classes in a way other people on your team might actually discover and use  Given that enums are classes like any other it shouldn   t be too surprising that you can extend them  like   enum Duration   Day  Week  Month     static class DurationExtensions      public static DateTime From this Duration duration  DateTime dateTime           switch  duration               case Day    return dateTime AddDays 1         case Week   return dateTime AddDays 7         case Month  return dateTime AddMonths 1         default     throw new ArgumentOutOfRangeException  duration                  I think enums are not the best choice in general but at least this lets you centralize some of the switch if handling and abstract them away a bit until you can do something better  Remember to check the values are in range too   You can read more here at Microsft MSDN

User · Answer

Of course you can  say for example  you want to use the DescriptionAttribue on your enum values   using System ComponentModel DataAnnotations   public enum Duration          Description  Eight hours        Day        Description  Five days        Week        Description  Twenty-one days         Month      Now you want to be able to do something like   Duration duration   Duration Week  var description   duration GetDescription       will return  Five days    Your extension method GetDescription   can be written as follows   using System ComponentModel  using System Reflection   public static string GetDescription this Enum value        FieldInfo fieldInfo   value GetType   GetField value ToString         if  fieldInfo    null  return null      var attribute    DescriptionAttribute fieldInfo GetCustomAttribute typeof DescriptionAttribute        return attribute Description

User · Answer

You can also add an extension method to the Enum type rather than an instance of the Enum        lt summary gt  Enum Extension Methods  lt  summary gt       lt typeparam name  T  gt  type of Enum  lt  typeparam gt  public class Enum lt T gt  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 lt Duration gt  Count    It s not a true extension method  It only works because Enum lt   is a different type than System Enum

User · Answer

You can create an extension for anything  even object although that s not considered best-practice   Understand an extension method just as a public static method  You can use whatever parameter-type you like on methods   public static class DurationExtensions     public static int CalculateDistanceBetween this Duration first  Duration last            Do something here

User · Answer

All answers are great  but they are talking about adding extension method to a specific type of enum   What if you want to add a method to all enums like returning an int of current value instead of explicit casting   public static class EnumExtensions       public static int ToInt lt T gt  this T soure  where T   IConvertible  enum               if   typeof T  IsEnum              throw new ArgumentException  T must be an enumerated type             return  int   IConvertible  soure               ShawnFeatherly funtion  above answer  but as extention method     public static int Count lt T gt  this T soure  where T   IConvertible  enum               if   typeof T  IsEnum              throw new ArgumentException  T must be an enumerated type             return Enum GetNames typeof T   Length            The trick behind IConvertible is its Inheritance Hierarchy see MDSN  Thanks to ShawnFeatherly for his answer

[c#] How to add extension methods to Enums

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