So in some ways this is simpler:. But are there any problems performance, purity, other? You sometimes read it's expensive to throw an exception but I am not sure whether the author means it's expensive to build in exceptions using the Throw keyword which I am not doing or whether he means it's expensive to allow exceptions to occur as I would be doing.
If would definitely test for Nothing instead of relying on exceptions here. You code indicates that the scenario where foo. That sort of gives the answer.
Throwing an exception is a relatively expensive operation from a performance perspective. This is the case regardless of wheter you are throwing it in your code, or if it is thrown in library code; it's exactly the same operation.
However, I would not keep from throwing exceptions for performance reasons unless I had a real, measured, critical business case. In my opinion this is mostly a matter of showing intent; by testing for Nothing and acting gracefully on that, your code expresses the fact that this is not a strange thing to happen.
If you are worried about the performance in executing foo. If so, there are probably ways of solving that your code sample already contains a suggestion.
If later find yourself repeating the same portion of the code often, you can wrap this lookup into a generic function, such as this:. As far as the cost of catching exceptions, here is a link to my answer on a different question. It gives you an idea of how catching exception impacts debugging performance and that of your Release build.
Semantically, you better avoid throwing exceptions if it's non-exceptional situation, as already mentioned in other answers. You should always try testing for nothing when you are expecting it as a controlled condition, only use catches where possible to handle unwanted errors I use unwanted broadly as some errors produce wanted results.
The ability to handle null strings without catching an exception is there so use it. In perspective of your choices, the second one is closest to what I would recommend, put your functions result into a holding variable, then test this variable using String.
IsNullOrEmpt y or if you want to include whitespace checking then String. IsNullOrWhiteSpace this also tests for empty strings too. These operators help you write less code to handle null checks, especially when descending into data structures. For example:. For comparison, the alternative code for the first of these expressions without a null-conditional operator is:. Sometimes you need to take an action on an object that may be null, based on the value of a Boolean member on that object like the Boolean property IsAllowedFreeShipping in the following example :.
You can shorten your code and avoid manually checking for null by using the null-conditional operator as follows:. The null-conditional operators are short-circuiting. Another use for null-conditional member access is to invoke delegates in a thread-safe way with much less code. The following example defines two types, a NewsBroadcaster and a NewsReceiver.
News items are sent to the receiver by the NewsBroadcaster. A String sometimes has no valid characters. The reference itself may be Nothing. And if a String does exist, it may be empty or have only whitespace characters. These situations are detected with String. We often use these functions in an If-Then statement. If Then. This Function returns a Boolean.
It checks the String argument against the Nothing constant. And it checks its Length as well. Otherwise it returns False.
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