How to indicate that a method was unsuccessful

Question

I have several similar methods, say eg. CalculatePoint(...) and CalculateListOfPoints(...). Occasionally, they may not succeed, and need to indicate this to the caller. For

Answer 1

I would say best practice is a return value means success, and an exception means failure.

I see no reason in the examples you provided that you shouldn't be using exceptions in the event of a failure.

Answer 2

To summarise there are a couple of approaches you can take:

1. When the return type is a value-type, like Point, use the Nullable feature of C# and return a Point? (aka Nullable), that way you can still return null on a failure
2. Throw an exception when there's a failure. The whole argument/discussion regarding what is and isn't "exceptional" is a moot point, it's your API, you decide what's exceptional behaviour.
3. Adopt a model similar to that implemented by Microsoft in the base types like Int32, provide a CalculatePoint and TryCalculatePoint (int32.Parse and int32.TryParse) and have one throw and one return a bool.
4. Return a generic struct from your methods that has two properties, bool Success and GenericType Value.

Dependent on the scenario I tend to use a combination of returning null or throwing an exception as they seem "cleanest" to me and fit best with the existing codebase at the company I work for. So my personal best practice would be approaches 1 and 2.

Answer 3

Return Point.Empty. It's a .NET design patter to return a special field when you want to check if structure creation was successful. Avoid out parameters when you can.

public static readonly Point Empty

Answer 4

If the failure is for a specific reason then I think its ok to return null, or bool and have an out parameter. If however you return null regardless of the failure then I don't recommend it. Exceptions provide a rich set of information including the reason WHY something failed, if all you get back is a null then how do you know if its because the data is wrong, you've ran out of memory or some other weird behavior.

Even in .net the TryParse has a Parse brother so that you can get the exception if you want to.

If I provided a TrySomething method I would also provide a Something method that threw an exception in the event of failure. Then it's up to the caller.