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kotlinlang

Untitled.kt

Hey all, have a quick question: if I have a class which has a property whose type will _always_ definitely be a certain type, is there a way I can specify that in my code so I don't have to do exhaustive when checks constantly? I tried using `as` but I couldn't get it to work, probably doing it wrong. My use-case:

You could put `when` into an extension property, e.g. `deviceScope`. That way `when` will still be there but you won't have to repeat yourself.

Thanks for the reply <@U0CP8EBRV>. I'm having a hard time visualizing your suggestion, could you provide a brief example perhaps?

```
open class Scope

class DeviceScope(val name: String) : Scope()

open class Fragment {
    val scope: Scope = DeviceScope("Example device scope")
}

val Fragment.deviceScope: DeviceScope
    get() {
        check(scope is DeviceScope) {
            "Non-DeviceScope scopes are not allowed"
        }
        return scope
    }

class MyFragment : Fragment() {
    init {
        println(deviceScope.name)
    }
}
```

`scope as DeviceScope` should work as well. I don't know why it wouldn't work for you. 

Thank you for the example <@U0CP8EBRV>! <@U9UUA8L66> I'm not sure, maybe I was doing something wrong when I tried it before. I'll try it again I suppose and see if that works

```
class MyFragment : Fragment() {
    init {
        (scope as DeviceScope).name
    }
}
```
This works but is again repetitive.
You could combine both to avoid it:
```
val Fragment.deviceScope: DeviceScope
    get() = scope as DeviceScope

class MyFragment : Fragment() {
    init {
        deviceScope.name
    }
}
```
I would leave my original one though with the `check(){}`, I think that makes the intent more obvious.

Ah okay, I see what I was doing now before when I was trying to use `as`. I was setting it to a value `val deviceScope = scope as DeviceScope` which was throwing a NPE... for reasons I'm still not sure I understand. When I use it like `(scope as DeviceScope).name` it works fine. I will probably make extension functions for Fragment class though as that is quite handy.

Yup, the extension properties work great and are very clean. Thanks again!

The issue with sealed classes is that you'd have to declare everything in the same file