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kotlinlang

is it an anti-pattern to use sealed classes/interfaces as an approximation of an algebraic data type? i've been doing things like below, but it seems that this causes `instanceof` checks -- so naturally various stack overflow answers mentioned "code smell", and i'm wondering if there's truth to that :slightly_smiling_face:
```sealed class Node

data class Leaf(x: Int): Node()
data class Tree(left: Node, right: Node?): Node()```

I do the same thing to get a DU type, it's really your only choice ( at least that I've found ) for that more functional style so far.

it also seems like `instanceof` is much more optimized than it used to be, so maybe this is more FUD than anything

Actually it's one of main usecases for sealed hierarchies

`instanceof` -checks of normal classes in Java is a code smell, `is`-checks of sealed classes in Kotlin isn't. Mostly because the compiler can check that you covered all cases, I guess. (maybe also because of smart cast :thinking_face:)