IEnumerable and loops
A bit of a rapid-fire question: if I only need to iterate on a collection once, is it OK to use IEnumerable? For example, using
Directory.EnumerateFiles(path) to filter out the files in separate lists.12 Replies
Unknown User•2w ago
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OK. But why would I use IEnumerable in a case like this, compared to saving the results to a List?
What do you mean?
If you only need to enumerate something, using IEnumerable gives more flexibility because the underlying type could be a List or an Array or a HashSet, etc.
Unknown User•2w ago
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The code doesn't care what the underlying type is.
Unknown User•2w ago
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It iterates on every entry in a collection.
Unknown User•2w ago
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I never used IEnumerator directly, oustide of LINQ and stuff like Directory.EnumerateFiles. So I was wondering if they could be used (and if yes, are they any performance penalties).
Unknown User•2w ago
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Using IEnumerable is fine. In fact it can be preferred. There is generally no performance issue.
IF the IEnumerable is backed by an expensive query then you may want to materialize it into a List or an Array if there is a chance you need to enumerate it more than once. Enumerating multiple times will cause the underlying query to be evaluated multiple times which can be a performance pitfall.
But if it's just backed by an in-memory data structure it's generally fine.
(Although usually if you can avoid enumerating something multiple times that is also preferred.)
Noted. Thank you very much.