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kotlinlang

It’s just saying that it can’t do the *smart* cast for you. As in: The compiler is not sure if curr.left is really a Node&lt;T&gt;. Should work fine with an explicit cast: `curr = curr.left as Node&lt;T&gt;`

yep, it works, you are right.
Very strange, that compiler can’t do smart cast in such simple case.
Anyway, thank you.

because compiler cannot guarantee you that this variable doesn’t changes (property getter can be dynamic, reflections)

you can cache it to local variable for smart cast:
```
   var curr = root
   val left = curr.left
   while (left != null) {
      curr = left
   }
   return curr```

+1 to local cache. I still don't know if that's best practice, but I often do that in these errors where it can't smart cast because it could change (even though that's highly unlikely in the time it takes to enter the if statement.)

imo it’s good practice and improve readability in many cases, much better than nested let for instance.
And of course help with smart cast