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Minimal Exceptions Types in .NET

The absolute minimum a new custom exception class needs to have is a name. Let’s say you are designing the login mechanism for a database application and as part of this job you need to create a custom exception which is thrown if a login attempt fails. A good name for such an exception would be LoginFailedException. An absolute minimum implementation in C# then looks like:

public class LoginFailedException: System.Exception
{
}

As you can see, all you need to do to create a basic custom exception is to derive from the Exception class. There’s only one problem with this definition. Since C# unfortunately doesn’t inherit constructors of base classes, this new type only has the standard constructor with no parameters and is therefore relatively useless. So, we need to add at least one constructor which does something useful:

public class LoginFailedException: System.Exception
{
   // The default constructor needs to be defined
   // explicitly now since it would be gone otherwise.

   public LoginFailedException()
   {
   }

   public LoginFailedException(string message): base(message)
   {
   }
}