A CloseableIterator which contains exactly one item.
Using some Closeable resource and a function to create a CloseableIterator from it, return a wrapped CloseableIterator which closes the resource when itself gets closed.
Using some Closeable resource and a function to create a CloseableIterator from it, return a wrapped CloseableIterator which closes the resource when itself gets closed. If the function terminates abnormally, the resource is closed immediately.
An empty CloseableIterator