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kotlinlang

why is this not compiling (complains about lateinit)?
```
class SpySleeper: Sleeper {
    lateinit var sleepDuration: Duration

    override fun sleep(d: Duration) {
        sleepDuration = d
    }
}

interface Sleeper  {
    fun sleep(duration: Duration)
}```

What error do you see? This compiles fine for me.

‘lateinit’ modifier is not allowed on properties of inline class types

Ah, okay. I missed the fact that `Duration` is `kotlin.time.Duration`.

neither can i add `?` after `Duration` to make it nullable

well, this `var sleepDuration: Duration = Duration.ZERO` seem to have worked

how about the old-style notNull-Delegate? It might work with inline classes!?
```var sleepDuration: Duration by Delegates.notNull()```
that's basically what you'd have used before there was `lateinit` .
<https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.properties/-delegates/not-null.html>