1-Old.kt

class Success(val result: Any)
class Failure(val message: String)

fun main() {
    val result = getResult()

    val something = when (result) {
        is Success -> {}
        is Failure -> {}
        else -> { /* Unnecessary part */ }
    }
}

fun getResult() = listOf(Success(""), Failure("Failed")).random()

2-New.kt

sealed class Result {
    class Success(val result: Any): Result()
    class Failure(val message: String): Result()
}

fun main() {
    val result = getResult()

    val something = when (result) {
        is Result.Success -> {}
        is Result.Failure -> {}
    }
}

fun getResult(): Result = listOf(Result.Success(""), Result.Failure("Failed")).random()