Associating Additional Information with .NET Enum

Question

My question is best illustrated with an example.

Suppose I have the enum:

public enum ArrowDirection {     North,     South,     East,     West } 

I want to associate the unit vector corresponding to each direction with that direction. For example I want something that will return (0, 1) for North, (-1, 0) for West, etc. I know in Java you could declare a method inside the enum which could provide that functionality.

My current solution is to have a static method -- inside the class that defines the enum -- that returns a vector corresponding to the passed in ArrowDirection (the method uses a HashTable to accomplish the lookup but that's not really important). This seems... unclean.

Question:
Is there a best-practice solution for storing additional information corresponding to an enum in .NET?

Answer 1

There's a FANTASTIC new way to do this in C# 3.0. The key is this beautiful fact: Enums can have extension methods! So, here's what you can do:

public enum ArrowDirection {     North,     South,     East,     West }  public static class ArrowDirectionExtensions {      public static UnitVector UnitVector(this ArrowDirection self)      {          // Replace this with a dictionary or whatever you want ... you get the idea          switch(self)          {              case ArrowDirection.North:                  return new UnitVector(0, 1);              case ArrowDirection.South:                  return new UnitVector(0, -1);              case ArrowDirection.East:                  return new UnitVector(1, 0);              case ArrowDirection.West:                  return new UnitVector(-1, 0);              default:                  return null;          }      } } 

Now, you can do this:

var unitVector = ArrowDirection.North.UnitVector(); 

Sweet! I only found this out about a month ago, but it is a very nice consequence of the new C# 3.0 features.

Here's another example on my blog.