Kotlin Sealed Classes Cheat Sheet

sealed class Result<out T>data class Success<T>(val data: T) : Result<T>()data class Error(val message: String, val cause: Throwable? = null) : Result<Nothing>()object Loading : Result<Nothing>()// Kotlin 1.9+: sealed interfaces work the same waysealed interface UiStatedata class Content(val items: List<String>) : UiStatedata object Empty : UiState   // 'data object' since 1.9 gives toString/equals for freedata object Loading2 : UiState

fun render(result: Result<String>): String = when (result) {    is Success -> "Data: ${result.data}"    is Error   -> "Failed: ${result.message}"    Loading    -> "Loading..."    // no `else` branch required — compiler errors if a case is missing}// Adding a new subclass later triggers a compile error at every `when`// that isn't updated — this is the main safety win over open classes.

sealed class NetworkResponse {    sealed class Success : NetworkResponse() {        data class Ok(val body: String) : Success()        object NoContent : Success()    }    data class Failure(val code: Int) : NetworkResponse()}fun handle(r: NetworkResponse) = when (r) {    is NetworkResponse.Success.Ok -> println(r.body)    NetworkResponse.Success.NoContent -> println("204")    is NetworkResponse.Failure -> println("error ${r.code}")}