Checking if no elements in IEnumerable(Of T) - Linq element and quantifier operators

Question

For my function

public static IEnumerable<CallbackListRecord> LoadOpenListToProcess(CallbackSearchParams usp){}

This line errors when the sequence contains no elements (as it should)

CallbackListRecord nextRecord = CallbackSearch.LoadOpenListToProcess(p).First();

I have changed it to the following

                CallbackListRecord nextRecord = null;
            IEnumerable<CallbackListRecord> nextRecords = CallbackSearch.LoadOpenListToProcess(p);
            if (nextRecords.Any())
            {
                nextRecord = nextRecords.First();
            }

Are there better, easier or more elegant ways to determine if the IEnumerable sequence has no elements?

Answer 1

You should try to avoid enumerating it more times than necessary (even if short-circuited, like First and Any) - how about:

var nextRecord = CallbackSearch.LoadOpenListToProcess(p).FirstOrDefault();
if(nextRecord != null) {
    // process it...
}

This works well with classes (since you can just compare the reference to null).

Answer 2

You can shorten the code to the following

var nextrecord = CallbackSearch.LoadOpenListToProcess(p).FirstOrDefault();

nextrecord will either contain the First element if there was one or null if the collection was empty.

Answer 3

If you are anticipating that there could be null values in the sequence, you could handle the enumerator yourself.

var enumerator = CallbackSearch.LoadOpenListToProcess(p).GetEnumerator();
if (enumerator.MoveNext()) {
  var item = enumerator.Current;
  ...
}