Sealed data class in Kotlin

Question

I have the following sealed classes

sealed class DownloadWallpaper : Result() {
    data class Progress(val hd: Boolean = false, ...) : DownloadWallpaper() 
    data class Success(val hd: Boolean = false, ...) : DownloadWallpaper()
    data class Error(val hd: Boolean = false, ...) : DownloadWallpaper()
}

And I am trying to do the following.

//obs is of type Observable<Detail.Result.DownloadWallpaper> 
obs.map{ it.copy(hd = true) }

But I cant, for two reasons since DownloadWallpaper isn't a data class. There's not .copy() method. How can I tell Kotlin that all classes in this seal class are in fact data classes?

Secondly, DownloadWallpaper it self doesn't have an 'hd' field. I could cast this using when How can fix this elegantly? This solution is quite ugly:

when (it) {
           is Detail.Result.DownloadWallpaper.Success -> it.copy(hd = true)
           is Detail.Result.DownloadWallpaper.Progress -> it.copy(hd = true)
           is Detail.Result.DownloadWallpaper.Error -> it.copy(hd = true)
 }

Answer 1

By adding a few abstract methods to your sealed class I was able to access copy methods without explicit type check. See for yourself:

sealed class DownloadWallpaper {
    abstract val hd: Boolean
    abstract fun copy(hd: Boolean): DownloadWallpaper
}

data class Progress(override val hd: Boolean = false, val a: Any) : DownloadWallpaper() {
    override fun copy(hd: Boolean) = copy(hd = hd, a = a)
}
data class Success(override val hd: Boolean = false, val s: String) : DownloadWallpaper() {
    override fun copy(hd: Boolean) = copy(hd = hd, s = s)
}
data class Error(override val hd: Boolean = false, val c: Int) : DownloadWallpaper() {
    override fun copy(hd: Boolean) = copy(hd = hd, c = c)
}

fun main() {
    val dw: DownloadWallpaper = Progress()
    val newDw = dw.copy(hd = false)
    val newDwSameHd = dw.copy(hd = dw.hd)
}