Both ```when it is EventDriver Stop gt is EventDriver Go gt ``` and ```when it EventDriver Stop gt EventDriver Go gt ``` seem to compile and run fine What s the difference I would have expected `is` to be required here

```when it is EventDriver Go gt accelerate it mph is EventDriver Stop gt stop it car ```

Both ```when it is EventDriver Stop gt is EventDriver Go gt kotlinlang #getting-started

08/14/2020, 6:58 AM

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

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?

08/14/2020, 7:31 AM

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

08/14/2020, 8:01 AM

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?

08/14/2020, 8:29 AM

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 -> ...
}

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

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

08/14/2020, 1:51 PM

Thanks @phldavies I think I will opt to ALWAYS omit the

is

when working with sealed classes and

when

08/14/2020, 2:07 PM

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

08/14/2020, 3:07 PM

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

brandonmcansh

08/14/2020, 9:21 PM

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.

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