Modeling and testing a basic stopwatch

[mcallisto]

Hi, I am new to Kyo.

I have modeled a very basic stopwatch (using also the Clock.Stopwatch case class).
My final goal would be to use it as a foundation for a client-side app.

The code can be seen here on Scastie https://scastie.scala-lang.org/mcallisto/29P0lehNTyCHOkHMWRvdmA/4

Questions I have in mind:

1. Is the code correct and idiomatic? I tested it and it works, but I would be more confident after some expert advice
2. Is the approach robust enough / recommended for a production app?
3. Does it make sense to test it with Clock.withTimeControl? Any hint on how to actually write such a simple test?

Thank you in advance for your ideas

[mcallisto]

Since I was not confident it worked 100%, I created an alternate version based on Clock.nowMonotonic

The new code on Scastie as well, see https://scastie.scala-lang.org/mcallisto/UJJDRcSgSSapscFjSr9LxA

[johnhungerford]

Hi @mcallisto -- sorry we missed this back in may. None of us have really been monitoring discussions...

1. Looks good to me! (That's how I would do it.) Maybe the only thing I would change is updateAndGetTotalElapsedTime to currentTime or something. The name exposes implementation details. I might also hide everything behind a trait.
2. Kyo isn't currently recommended for production, but it looks pretty solid to me
3. Yes I would test with Clock.withTimeControl:

Clock.withTimeControl: timeControl =>
  for
    stopWatch <- AltStopWatch.create
    initialTimeStopped <- stopWatch.updateAndGetTotalElapsedTime
    _ <- timeControl.advance(1.hour)
    timeAfterOneHourStopped <- stopWatch.updateAndGetTotalElapsedTime
    _ <- stopWatch.start
    timeAfterStarted <- stopWatch.updateAndGetTotalElapsedTime
    _ <- timeControl.advance(1.hour)
    timeAfterOneHourStarted <- stopWatch.updateAndGetTotalElapsedTime
    _ <- stopWatch.reset
    timeAfterReset <- stopWatch.updateAndGetTotalElapsedTime
    _ <- timeControl.advance(30.minutes)
    timeAfterThirtyMinsAfterReset <- stopWatch.updateAndGetTotalElapsedTime
  yield assert(
     initalTimeStopped == Duration.Zero
       && timeAfterOneHourStopped == Duration.Zero
       && timeAfterStarted == Duration.Zero
       && timeAfterOneHourStarted == 1.hour
       && timeAfterReset == Duration.Zero
       && timeAfterThirtyMinsAfterReset == Duration.Zero
  )

[fwbrasil]

LGTM as well! A few suggestions:

• There's use of flatMap in a few places. We recommend map instead since it supports both non-effectful and effectful functions. Basically map == flatMap.
• We typically name constructor methods init instead of create or make in case you want to keep a similar naming
• I'd return a Bollean < IO in start indicating if it was successful. If the condition should never happen, maybe aborting is better
• It seems both versions with Clock.Stopwatch and Clock.nowMonotonic should work fine
• In the version with Clock.nowMonotonic it seems you could use Duration directly instead of transforming it to Long since it has + and - methods.

Kyo isn't currently recommended for production, but it looks pretty solid to me

@johnhungerford I wouldn't say Kyo isn't recommended for production since we're now going to avoid major breaking changes but it's important to keep in mind that it isn't still 1.0. There isn't a binary compatibility guarantee yet and migration to new versions might still require adaptations or executing scalafix migration rules.

[mcallisto]

Thank you @johnhungerford and @fwbrasil for your detailed replies!

Sorry for starting the Discussions empty space 😅, if it was not intended for this. Hope the question was interesting enough for a place in the Q&A category.

In general I think some space where questions like this can be filed (and not lost) is needed. I know @fwbrasil is quite active on Discord but it is a little bit too chaotic there on the Scala channels without threads. Maybe I could have posted it to Stack Overflow but here it felt more like "home".