Question

I’m wondering about best practice here. Is it good practice for a factory method to return null if it can’t create anything? Here’s an example:

ICommand command = CommandFactory.CreateCommand(args);
if (command != null)
    command.Execute();
else
    // do something else if there is no command

An alternative would be to return a NullCommand or something, I guess, but what is best practice?

Answer 1

I think it’s potentially reasonable for a factory method to return null in some situations, but not if it’s a method called CreateCommand. If it were GetCommand or FetchCommand, that might be okay… but a Create method should throw an exception on failure, I would suggest.

Whether you really want it to return null in this situation depends on the bigger picture, of course. (Is there a reasonable null object implementation you could return instead, for example?)