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In my everlasting quest to suck less I'm trying to understand the "yield" statement, but I keep encountering the same error. The body of [someMethod] cannot be an iterator block because 'System.Collections.Generic.List< AClass>' is not an iterator interface type. This is the code where I got stuck: foreach (XElement header in headersXml.Root.Elements()){ yield return (ParseHeader(header)); } What am I doing wrong? Can't I use yield in an iterator? Then what's the point? In this example it said that List<ProductMixHeader> is not an iterator interface type. ProductMixHeader is a custom class, but I imagine List is an iterator interface type, no? --Edit-- Thanks for all the quick answers. I know this question isn't all that new and the same resources keep popping up. It turned out I was thinking I could return List<AClass> as a return type, but since List<T> isn't lazy, it cannot. Changing my return type to IEnumerable<T> solved the problem :D A somewhat related question (not worth opening a new thread): is it worth giving IEnumerable<T> as a return type if I'm sure that 99% of the cases I'm going to go .ToList() anyway? What will the performance implications be?

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