JEP 473: Proposal for new built-in gatherer `indexed`

[Henrik Wall]

Hey folks,

Not having access to the index of an element of a stream is often a
reason to fall back to a traditional loop, at least for me. I'd love
to have `Gatherers.indexed()` that looks something like this:

public static <TR> Gatherer<TR, ?, Map.Entry<Integer, TR>> indexed() {
    return Gatherer.ofSequential(
            () -> new int[1],
            Gatherer.Integrator.ofGreedy((state, element, downstream) ->
                    downstream.push(Map.entry(state[0]++, element)))
    );
}

(Potentially with a custom pair class to avoid auto-boxing.)

In other popular languages like Python or Rust, this is also called `enumerate`.

Any chance to get that in a future release?

Regards,
Henrik