C#: Where to implement a custom IEnumerator<T>

Question

Say I have a class that implements IEnumerable<T>. It currently uses the yield keyword in the GetEnumerator() method. But now I need to do a bit more, for example I would like to clean up after myself. To do this, unless I have overlooked anything, I need to implement the IEnumerator<T> interface. But where would you say I should do that?

Should the class itself implement it and GetEnumerator() return this? Or would it be better to hide it in a private class? Or should it maybe just be an entirely different class? What are some common practices to this?

Answer 1

I would go with a class for the IEnumerator<T>. This will need to store state (current position) that is not part of the collection, but rather part of the process of enumerating.

Answer 2

If all you need to do is clean up some resources when the enumerator is disposed of, like at the end of a foreach loop, then you can do that with what you have, just add a try/finally block to your iterator method.

Like this:

public IEnumerator<T> GetEnumerator()
{
    try
    {
        // your iterator code here
    }
    finally
    {
        // cleanup code here
    }
}

That's all there is to it.

Answer 3

You may not need to write class for this at all. An iterator method can return IEnumerable<T>, so if your class only needs to implement IEnumerable<T> and nothing else, just write an iterator method for the whole thing.

If not, and you have to stick with an outer class that implements IEnumerable<T> by having an iterator method to do GetEnumerator, then you don't have to do anything very difficult to clean up after iteration.

IEnumerator<T> derives from IDisposable. An iterator method implements Dispose by executing finally blocks or any code after the last yield return.