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`sealed class` vs `enum` — when would you choose `sealed`?

Tags

#sealed#enum#when

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Answer

Use `sealed` when you need a closed set of variants that can carry different data and types (sum type). It enables exhaustive `when` checks, while `enum` is a fixed set of instances of one type.

sealed interface Result

data class Ok(val value: Int) : Result

data class Err(val message: String) : Result

fun handle(r: Result) = when (r) {
  is Ok -> r.value
  is Err -> 0
}

Advanced answer

Deep dive

Use `enum` when you need a small fixed set of constants of one type (singletons).

Use `sealed` when variants can have different shapes/data:

`sealed interface Result { data class Ok(val v: Int): Result; data class Err(val msg: String): Result }`

Benefits of `sealed`:

Exhaustive `when` (compiler can force handling all cases).
Each variant can carry different fields and behavior.

Common pitfalls

Using enums to model cases that need payload (you end up with nullable fields / awkward state).
Forgetting that sealed is “closed”: subclasses must be in the same package/module (depending on Kotlin version).

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