which is better, using a nullable or a boolean return+out parameter

Question

Lets say I have a function that needs to return some integer value. but it can also fail, and I need to know when it does.

Which is the better way?

public int? DoSomethingWonderful()

or

public bool DoSomethingWonderful(out int parameter)

this is probably more of a style question, but I'm still curious which option people would take.

Edit: clarification, this code talks to a black box (lets call it a cloud. no, a black box. no, wait. cloud. yes). I dont care why it failed. I would just need to know if I have a valid value or not.

Answer 1

I like the nullable version better, because you can use the null coalesce operator ?? on it, e.g.:

int reallyTerrible = 0;
var mightBeWonderful = DoSomethingWonderful() ?? reallyTerrible;

Answer 2

It depends on how you think the calling code should look like. And therefore what your function is used for.

Generally, you should avoid out arguments. On the other hand, it could be nice to have code like this:

int parameter;
if (DoSomething(out paramameter))
{
  // use parameter
}

When you have a nullable int, it would look like this:

int? result = DoSomething();
if (result != null)
{
  // use result
}

This is somewhat better because you don't have an out argument, but the code that decides if the function succeeded doesn't look very obvious.

Don't forget that there is another option: use Exeptions. Only do this if the case where your function fails is really an exceptional and kind of a error-case.

try
{
  // normal case
  int result = DoSomething()
}
catch (SomethingFailedException ex)
{
  // exceptional case
}

One advantage of the exception is that you can't just ignore it. The normal case is also straight forward to implement. If the exceptional case something you could ignore, you shouldn't use exceptions.

Edit: Forgot to mention: another advantage of an Exception is that you also can provide information why the operation failed. This information is provided by the Exception type, properties of the Exception and the message text.