Question

I have a question that I am surprised hasn’t already been asked in exactly this format.

If I have an IEnumerable that is generated based on iterating through a source of data, (and using a yield return statement), how can I detect when there has been a modification to the source after an access via an Enumerator that was generated via a GetEnumerator call?

Here is the strange part: I’m not multi-threading. I think my question has a flaw in it somewhere, because this should be simple. . . I just want to know when the source has changed and the iterator is out of date.

Thank you so much.

Answer 1

You would need to handle creating the enumerator yourself in order to track this information, or, at a minimum use yield return; with your own type of modification tracking in place.

Most of the framework collection classes, for example, keep a “version” number. When they make an enumerator, they keep a snapshot of that version number, and check it during MoveNext(). You could make the same check before calling yield return XXX;