lihaoyi/scala.rx

An experimental library for Functional Reactive Programming in Scala

Peng Li

@freewind

Hi guys, I have some questions when testing scala.rx code, and post a question here: https://stackoverflow.com/questions/49073908/how-to-test-vars-of-scala-rx-with-scalatest

Thanks for helping

Nick Childers

@Voltir

@freewind i took a stab at answering it, let me know if you want any clarification

Peng Li

@freewind

@Voltir Thanks for your answer! It gives me some idea and I changed my test using scalatest's AsyncTestSuite and the code is:

test("watchOrders") {
  var result = List.empty[Order]
  val stream = client.watchOrders()
  val promise = Promise[Assertion]()
  stream.fold(List.empty[Order]) {
    case (acc, Some(elem)) =>
      val result = elem :: acc
      println("result size: " + result.size)
      if (result.size == 4) promise.success({
        assert(validateTheOrders(result))
      })
      result
  }
  promise.future
}

The good new is if the validateTheOrders(result) is passed, the test will pass and terminate as expected

But if the assertion is false, it will never stop, and the result size printed in console will be:

result size: 1
result size: 2
result size: 3
result size: 4
result size: 4
result size: 4
result size: 4
...

Peng Li

@freewind

@Voltir I just make it work inspired with the eventually method from haoyi's utest. Now I'm still using scalatest's SyncTestSuit, and the code is like:

  private def waitUntil[T](stream: Rx[T])(cond: T => Boolean, maxWait: Duration): T = {
    val promise = Promise[T]()
    Executors.newSingleThreadScheduledExecutor().scheduleAtFixedRate(() => {
      val list = stream.now
      if (cond(list)) {
        promise.success(list)
      }
    }, 0L, 100L, TimeUnit.MILLISECONDS)
    Await.result(promise.future, maxWait)
  }

  test("watchOrders") {
    val stream = client.watchOrders()
    val listRx: Rx[List[Order]] = stream.fold(List.empty[Order]) {
      case (acc, Some(elem)) => elem :: acc
      case (acc, _) => acc
    }
    val list = waitUntil(listRx)(_.size >= 4, 10.seconds)
    assert(validateTheOrders(list))
  }

It's working great now

Nick Childers

@Voltir

@/all scala.rx 0.4.0 was published

scalway

@scalway

@Voltir where? I cannot find sources.

Oh... there is still old documentation & there is no github release :).

moritz bust

@busti

Why do I have to have an implicit Owner in scope when using rx.fold()() in a class / trait, but not when I use it elsewhere? Can I avoid that somehow?

scalway

@scalway

https://github.com/lihaoyi/scala.rx#ownership-context

This is how scala.rx fights against memory leaks

moritz bust

@busti

Well yes, but if I understand it correctly, the context is generated automagically via macros most of the time? When I use fold in a repl, I do not need to declare an ownership context...

Is it okay to just include an implicit val ctx = Ctx.Owner.save() in my class? I have seen that somewhere...
But unfortunately .save() lacks documentation.

moritz bust

@busti

In this example:

class Foo {
  val a = Var(0)

  val b = a.fold(1)(_ * _)
}

how do I obtain / define / pass an Ownership Context?
It just is not very clear to me.

Nick Childers

@Voltir

Pass it in as an implicit class param on Foo

moritz bust

@busti

@Voltir But where does that implicit come from? I am not using any rx's elsewhere...

Nick Childers

@Voltir

so, if you have some object:

object Main {
  val foo = new Foo()
}

you will get a context for free

(magic macro stuff happens to make that possible)

if you are inside a class, then you can again make that outer class take an implicit ctx

if you know for sure that Foo (or the class that wraps it) is going to be instantiated a finite number of times, then its safe to use the "unsafe" owner ctx

moritz bust

@busti

That is what I wanted to know, thanks a lot!

sidnt

@sidnt

Weird: I've done import rx._ but my code says not found: value Obs in this code piece for providing the implicit conversion.

sidnt

@sidnt

Oh. So this:
https://stackoverflow.com/questions/35752639/scala-rx-with-scalatags-example-compilation-error

moritz bust

@busti

How would I merge two rx's of the same type into a single one, that updates whenever either of the source Rx's updates?

Sakib Hadžiavdić

@sake92

Hi all!, I'm struggling with this snippet: https://github.com/lihaoyi/hands-on-scala-js/blob/master/examples/demos/src/main/scala/advanced/BasicRx.scala#L68-L79

It's using "scalarx" % "0.2.8", but latest is "0.4.0"

This is what I got so far:

implicit def rxFrag[T](r: Rx[T])(implicit dataCtx:  Ctx.Data, ev: T => Frag): Frag = {
    import Ctx.Owner.Unsafe._

    def rSafe: dom.Node = span(r()).render

    var last = rSafe
    r.triggerLater {
      val newLast = rSafe
      js.Dynamic.global.last = last
      last.parentNode.replaceChild(newLast, last)
      last = newLast
    }

    last
  }

but now even the simplest code requires this implicit Ctx.Data...

Simon Morgan

@simon-morgan

@lihaoyi and other contributors, thank you for an excellent library. I'm more productive and concise than every I was with scalajs-react and scala.binding.

@lihaoyi will you be at ScalaDays Lausanne in a few weeks? Any one else who uses scala.rx going to be there? It would be great to meet up, discuss experiences and share a drink!! If you are interested, please post!!!

Kamil Kloch

@kamilkloch

Hi! I am struggling with generating table rows wrapped within Rx construct. The following code
```scala
Rx {
for (row <- rows()) yield tr(...)
}

produces a sequence of tr elements wrapped within an extra span. This kills the table column layout. Thanks in advance for any tips!

Rx {
for (row <- rows()) yield tr(...)
}

Marc Grue

@marcgrue

Wrapping a single element should do the trick I think:

Rx {
  tbody(
    for (row <- rows()) yield tr(...)
  )
}

Kamil Kloch

@kamilkloch

@marcgrue Thanks :)

Michal Lacko

@visox

hi, any chance for 2.13 ??

Grant

@gavares

+1 ^^. I know macro updates are tough but Scala.rx + scalatags seems like a great pairing to have available

I’m suffering from a recursion bomb right now with Scala.rx and I’m a bit unclear on Ctx.Owner and Ctx.Data which I suspect are somehow related. I know there are some open tickets related to documentation on that stuff. I’d be more than happy to translate a discussion here into a PR for the docs.

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