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No, because an iterator block is simply a state machine built on your behalf by the compiler. This feature allows you to "yield" and item as a portion of a sequence.
If the return type was other than IEnumerable<T> (like IDictionary for example) the compiler would have to generate methods to implement that interface and at that point it wouldn't make much sense because you would be working with a collection rather than a sequence.
nope, just ienumerable :-)