Operator TakeUntil with predicate

[akarnokd]

Take values and check the condition after the value is emitted.

For enhancement request #1649.

[benjchristensen]

Thanks for adding this! Not convinced on the name though. The 'do' prefix is used to represent side-effects everywhere else. I think the prefix should still be take-something.

[akarnokd]

The question then remains, should it stop if predicate turns into false or should it stop if predicate turns into true? Because, classically do { } while (true) and repeat until false (Pascal).

[benjchristensen]

I like it how it's currently implemented ... do until true.

It fits the "takeUntil" term ... "take until a value == predicate".

        System.out.println("------------------------");
        Observable.just(1, 2, 3, 4, 5, 6, 7)
                .doOnEach(System.out::println)
                .takeUntil(i -> i == 3)
                .forEach(System.out::println);

        System.out.println("------------------------");
        Observable.just(1, 2, 3, 4, 5, 6, 7)
                .doOnEach(System.out::println)
                .takeWhile(i -> i <= 3)
                .forEach(System.out::println);

That code shows the difference with takeWhile and it works well. We emit 1, 2, 3 and then stop.

------------------------
[rx.Notification@891cd479 OnNext 1]
1
[rx.Notification@891cd47a OnNext 2]
2
[rx.Notification@891cd47b OnNext 3]
3
------------------------
[rx.Notification@891cd479 OnNext 1]
1
[rx.Notification@891cd47a OnNext 2]
2
[rx.Notification@891cd47b OnNext 3]
3
[rx.Notification@891cd47c OnNext 4]