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.NET Forum / Languages / C# / August 2007Why can we use foreach without IEnumerator/IEnumerable
Why was this design decision to use this kind of "duck typing" in that case? All you have to do is have a method GetEnumerator() which returns an object providing Current and MoveNext(). IEnumerator and IEnumerable are not necessary. Why is that? And what are these interface good for then? Just dummy/marker interfaces like Cloneable in java? The interface is handy for when you need to talk about an abstract "something that is enumerable, but I don't know what yet" - for instance in the ctor of List<T>(IEnumerable<T>) I can't explain the duck-typing ;-p Marc > Why was this design decision to use this kind of "duck typing" in that case? So that you could do strongly typed enumerations (including there being no boxing penalty) before generics came along. I suspect that if it was designed today with generics already present, it wouldn't be done the same way. Having said that, I believe the query expression transformations performed by the C# 3 compiler require appropriate method names but not any particular interface. > All you have to do is have a method GetEnumerator() which returns an > object providing Current and MoveNext(). IEnumerator and IEnumerable are > not necessary. Why is that? And what are these interface good for then? > Just dummy/marker interfaces like Cloneable in java? No, there are lots of things which *do* require IEnumerable. It's not just for foreach! Jon >> Why was this design decision to use this kind of "duck typing" in that case? > [quoted text clipped - 5 lines] > query expression transformations performed by the C# 3 compiler > require appropriate method names but not any particular interface. Yes, I also heard of that. >> All you have to do is have a method GetEnumerator() which returns an >> object providing Current and MoveNext(). IEnumerator and IEnumerable are [quoted text clipped - 5 lines] > > Jon Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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