If an exception is thrown from IEnumerator<T>.MoveNext() or .Current, must it be still be disposed?

Question

Intuitively I think yes, but I'm not sure if there's some convention I don't know about.

Answer 1

Since we can't know what the implementation is, the only safe answer is "yes".

However, it is very rare to use IEnumerator directly - foreach being more common. For the generic IEnumerator<T> you can use a using statement:

using(var iter = obj.GetEnumerator()) {
    ...
}

Even without the generic version, you can cheat:

IEnumerator iter = obj.GetEnumerator();
using(iter as IDisposable) {
    ...
}

Which will dispose iter if it is IDisposable

Answer 2

No disposable object MUST be disposed, ever.^[1]

But they should be. As a using block uses the finally clause to dispose and this is executed whether the using block is exited normally or via an exception, the default is to dispose even in the face of an exception.

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^[1] I suppose one could have a buggy implementation where a non-managed resource is held and there is no finaliser, but the correct action there is to implement a finaliser.