Operator: takeUntil

[OliverJAsh]

Hi!

Are there plans to add a takeUntil operator to this library?

If so, I was wondering if we would have inclusive (take until and including) and exclusive versions (take until and excluding the first falsy predicate).

[OliverJAsh]

An example of where this would be useful:

[1,2,3,4].takeUntil(x => x >= 3)
// [ 1, 2 ]
[1,2,3,4].takeUntilInclusive(x => x >= 3)
// [ 1, 2, 3 ]

I'm not sure if takeUntilInclusive is a bad idea or not, or it the same can be achieved with other operators?

[OliverJAsh]

Upon investigation, it looks like takeWhileInclusive might be a better idea here: http://stackoverflow.com/a/22472610/5932012

[mattpodwysocki]

@OliverJAsh added takeUntil as per spec for AsyncIterableX

[OliverJAsh]

Hi @mattpodwysocki. The takeUntil included accepts a promise parameter, however I would like a version that accepts a function parameter, like what you see in RxJava http://reactivex.io/RxJava/javadoc/rx/Observable.html#takeUntil(rx.functions.Func1)

Would you consider adding this?

[OliverJAsh]

To anyone who comes here needing this. Here's a custom implementation you can use:

export const takeUntil = <T>(fn: (value: T) => boolean) => (
    asyncIterable: AsyncIterable<T>,
): AsyncIterable<T> =>
    Ix.AsyncIterable
        .from(asyncIterable)
        .map(value => {
            const shouldEnd = fn(value);
            return shouldEnd
                ? [{ value, done: false }, { value: undefined, done: true }]
                : [{ value, done: false }];
        })
        .flatMap(iterable => Ix.AsyncIterable.from(iterable))
        // We know `value` has type `T` because of the `takeWhile` guard
        // https://github.com/ReactiveX/IxJS/issues/44
        .takeWhile(x => !x.done)
        .map(({ value }) => value as T);

[OliverJAsh]

Similar feature request for RxJS, which seems to have a good amount of support: ReactiveX/rxjs#2420.

If I sent a PR for this, would it be reviewed and potentially accepted?

Related: https://github.com/martinsik/rxjs-plus#takewhileinclusive

[trxcllnt]

@OliverJAsh yes, definitely! @mattpodwysocki might have more time than me, I'm pretty slammed till the end of the month, but we should be able to work it in.