Both ```when (it) { is EventDriver.Stop ->...

# getting-started

[Colton Idle]

Both

when (it) {
    is EventDriver.Stop -> ...
    is EventDriver.Go -> ...
}

and

when (it) {
    EventDriver.Stop -> ...
    EventDriver.Go -> ...
}

seem to compile and run fine. What's the difference? I would have expected is to be required here?

[phldavies]

The first is doing a type check, the second is doing equality.

[Colton Idle]

Hm. I'm not sure which one I want? I'm just sending an eventDriver type which is a sealed class. Is there a typical route to use here?

[phldavies]

if it’s a sealed class with only object leafs, equality is fine. If you had something like:

sealed class EventDriver {
  sealed class Go: EventDriver() {
    object Forward: Go()
    object Backward: Go()
  }
  object Stop: EventDriver()
}

Then you would either want to do:

when(it) {
  EventDriver.Stop -> ...
  EventDriver.Go.Forward -> ...
  EventDriver.Go.Backward -> ...
}

or

when(it) {
  is EventDriver.Go -> ...
  EventDriver.Stop -> ...
}

[phldavies]

You can still do type checking with Stop for consistency if you wanted, as only that single object will satisfy the type check, but the is in that case would be superfluous

[Colton Idle]

Thanks @phldavies I think I will opt to ALWAYS omit the is when working with sealed classes and when statement

[nanodeath]

the sealed class part isn't the key part here -- it's that the "classes" you're testing are in fact objects.

[Colton Idle]

Oh. So its that I have objects... this is making more sense.

[brandonmcansh]

If you have data classes in your sealed class will auto type cast it when using is and give you direct access to its members.

[brandonmcansh]

when (it) {
   is EventDriver.Go -> accelerate(it.mph)
   is EventDriver.Stop -> stop(it.car)
}