In C# is default case necessary on a switch on an enum?

Question

I've seen posts relating to C++, but am asking specifically for C# .NET (4.0+).

In the following example is a default case necessary?

public enum MyEnum : int {     First,     Second }  public class MyClass {      public void MyMethod(MyEnum myEnum)     {         switch (myEnum)         {             case MyEnum.First: /* ... */ break;             case MyEnum.Second: /* ... */ break;              default: /* IS THIS NECESSARY??? */ break;         }     } } 

Answer 1

It's a common misconception that .Net enum values are limited to the ones declared in the Enum. In reality though they can be any value in the range of the base type of the enum (int by default). For example the following is perfectly legal

MyMethod((MyEnum)42); 

This code will compile without warnings and hit none of your case labels.

Now whether your code chooses to handle this type of scenario is a policy decision. It's not necessary but I'd certainly recomend having one. I prefer to add a default to every switch on enum I write specifically for this scenario with the following pattern

switch (value) {    ...   default:      Debug.Fail(String.Format("Illegal enum value {0}", value));     FailFast();  // Evil value, fail quickly  }