when()

sealed class

sealed class NetworkOperationResult {
    class success(body: String): NetworkOperationResult()
    class failure(error: Throwable?): NetworkOperationResult
}

sealed class DriveWriteResult {
    object success: DriveWriteResult()
    object notEnoughSpace: DriveWriteResult()
    object insufficientPermissions: DriveWriteResult()
    object nonexistentDirectory: DriveWriteResult()
    class unknownFailure(error: Throwable): DriveWriteResult()
}

var netResult = myFancyNetworkOperation()
when (netResult) {
    is success -> print(netResult.body) // error
    is failure -> showAlert("Failure due to ${netResult.error ?: "an unknown error"}")
}

val writeResult = myFancyDriveWrite()

if (writeResult is success) { // error
    return
}
else {
    showAlert("Could not save: ${writeResult}")
}

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sealed class FacebookStatus

fun changeViewState()

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sealed class NewUserViewMode

FacebookStatusLoading

NewUserViewModeLoading