Applying scan after delay will delay the initial value

[mbrandonw]

Consider the following observable:

Observable.just(1)
  .delay(10, TimeUnit.Seconds)
  .scan(2, (accum, x) -> accum + x)

I would expect this to emit 2 immediately, and then 10 seconds later emit 3. Instead it waits 10 seconds, and then emits 2 and 3 immediately.

Am I interpreting this incorrectly?

[artem-zinnatullin]

You're delaying emission of just(1), then operator scan() does it's job and emits two values without delay.

Try:

Observable
  .just(1)
  .scan(2, (accum, x) -> accum + x)
  .delay(10, SECONDS)

[akarnokd]

This is a bug with the scan operator emitting its initial value only when the first value arrived and has been fixed via #3171. It will be part of the next release.

[mbrandonw]

Thanks @akarnokd. I only just realized this issue is related to #3168, which I also filed.

So just to confirm, the expected behavior of scan is to emit the initial value immediately, and then the accumulated values as they come?

[akarnokd]

Exactly.

[mbrandonw]

perf thanks!