Why no index or observable arguments in scan's accumulator?

[rickmed]

Sorry if this kind of question is out of place or out of format.

[kwonoj]

I don't recall why index is missing, but in general in RxJS 5 passing source observable is dropped by it doesn't have much use cases in general. It'd be appreciate if you can elaborate bit more if you'd like to have it, or else.

In case of index, it can be easily retrieved via accumulator of scan, something like

Rx.Observable.of('a','b','c','d').scan((acc, value) => {
  acc.idx++;
  acc.value = value;
  return acc;
}, { idx : -1, value: null }).subscribe(x => {
  console.log(`index: ${x.idx}, value: ${x.value}`);
});

(just wrote in a hurry only for pseudo purpose)

[rickmed]

@kwonoj I ended up doing something like that in my case but it felt forced. I understand the drop of observable but all (most?) of the operators with selector functions have an index argument, no?

[kwonoj]

Most of operators requiring predicate passes its index, yes. Some of resultSelectors are not while. For this one I don't have exact answers though. /cc @Blesh

[staltz]

I believe we could add at least the index without any negative impact. Should be there IMO.

[kwonoj]

I agree it can be added, just curious if there was reason to not to.

[lock]

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