sealed_classes_enum.kt

enum class ScreenState {
    LOADING,
    ERROR,
    SUCCESS
}

class Response(val state: ScreenState, val data: String?, val error: Throwable?)

fun main(args: Array<String>) {

    val response = Response(ScreenState.SUCCESS, "yay", null)

    when (response.state) {
        ScreenState.SUCCESS -> doStuff(response.data!!)
        ScreenState.LOADING -> { }
        ScreenState.ERROR -> { }
    }
}

fun doStuff(data: String) {
    //NO-OP
}