# IT:AD:Patterns:Enums Start with Undefined Strategy #



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## Process ##

Consider 

<sxh>
public enum Gender{
  Male =1,
  Female =2
}
</sxh>

Much as you don't want to admit it...zero's are a common source of bugs. So if your code somehow ends up setting a property to:

<sxh>
  person.Gender=  (Gender)0
</sxh>

You'll be surprised to know that it won't complain, even if 0 is not a member of the enum list.

The only way that you can Validate such a scenario is by doing something like the following.

<sxh>
public static void Validate(this Person person){
   if ( ((int)person.Gender) == 0){throw ....}
}
</sxh>

which of course nobody will do (as they'll be thinking about using the enum, not the unitituive int).


So just account for the use of a zero getting in there somehow. Put it at the beginning of the enum:


<sxh>
public enum Gender{
  Undefined=0
  Male =1,
  Female =2
}
</sxh>

Now you can test for it. 

<sxh>
public static void Validate(this Person person){
   if (person.Gender == Gender.Undefined){throw ....}
}
</sxh>


While you're at it, you might as well consider whether there is such a case as Unknown. In which case, give it a value of 1:

<sxh>
public enum Gender{
  Undefined=0,
  Unknown=1,
  Male =2,
  Female =3,
}
</sxh>


Now it's clearer.