Hey all, have a quick question: if I have a class which has a property whose type will always defini...

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[Shan]

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:

Untitled.kt

[Czar]

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.

[Shan]

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

[Czar]

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)
    }
}

[SiebelsTim]

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

[Shan]

Thank you for the example @Czar! @SiebelsTim 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

[Czar]

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.

[Shan]

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.

[Shan]

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

[Hamza]

Use sealed classes

[LeoColman]

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

[LeoColman]

Perhaps it gets somewhat ugly