scalaobservablerx-scala

Observables created at time interval

I was looking at the RxScala observables which are created at a given time interval:

val periodic: Observable[Long] = Observable.interval(100 millis)

periodic.foreach(x => println(x))

If I put this in a worksheet, I get this result:

periodic: rx.lang.scala.Observable[Long] = rx.lang.scala.JavaConversions$$anon$2@2cce3493

res0: Unit = ()

This leaves me confused: What do the elements of periodic actually contain?

Do they contain some index? Do they contain the time interval at which they were created?

Solution

  • As you can read here http://reactivex.io/documentation/operators/interval.html produced elements are Long values incrementing from 0.

    As for your code and results:

    Here, you create the observable, and get Observable[Long] assigned to periodic. Everything as expected.

    scala> val periodic: Observable[Long] = Observable.interval(100 millis)
periodic: rx.lang.scala.Observable[Long] = rx.lang.scala.JavaConversions$$anon$2@2cce3493

    Here, you register a callback, i.e. what happens when value is emmited. The return type of foreach method is Unit as it doesn't have a reasonable value and happens just for the side effect of registering callbacks.

    periodic.foreach(x => println(x))
res0: Unit = ()

    You don't see actual values because execution stops. Try to insert Thread.sleep.

    val periodic: Observable[Long] = Observable.interval(100.millis)
periodic.foreach(x => println(x))
Thread.sleep(1000)

    Gives output similar to

    periodic: rx.lang.scala.Observable[Long] = rx.lang.scala.JavaConversions$$anon$2@207cb62f

res0: Unit = ()

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res1: Unit = ()