> For example every element may have an epoch, and every time a new element is added the epoch is incremented. Then what you could do is to only remember elemen

> For example every element may have an epoch, and every time a new element is added the epoch is incremented. Then what you could do is to only remember elements with epoch <= the epoch at which you started iterating, so that all the new elements will not be returned. Do that and you will immediately have people wanting an equally transaction-like view of the iteration set in the face of updates. I think it's best to draw the line where you have and be specific about what this is or is not intended to support.