How to make closed classes generic in Kotlin?
Can I use the AsyncResult class below to prevent UserDataAppResult and CreateUserResult from overriding InFlight, Error and InFlight?
//TODO: use this to make the below classes generic?
sealed class AsyncResult{
object InFlight : AsyncResult()
data class Error(val errorMessage: String) : AsyncResult()
data class Loaded<out T>(val users: T) : AsyncResult()
}
sealed class UserDataAppResult : AppResult() {
object InFlight : UserDataAppResult()
data class Error(val errorMessage: String) : UserDataAppResult()
data class Loaded(val users: List<User>) : UserDataAppResult()
}
sealed class CreateUserResult : AppResult() {
object InFlight : CreateUserResult()
data class Error(val errorMessage: String) : CreateUserResult()
data class Loaded(val users: User) : CreateUserResult()
}
Is it possible for the above code to look like this?
sealed class AsyncResult{
class InFlight : AsyncResult()
data class Error(val errorMessage: String) : AsyncResult()
data class Loaded<out T>(val users: T) : AsyncResult()
}
sealed class UserDataAppResult : AsyncResult()
sealed class CreateUserResult : AppResult()
val activeUsers: Flowable<UserDataAppResult> = appDatabase.userDao().getActiveUsers(appSettings.currentLanguage.ordinal)
.map<UserDataAppResult> { UserDataAppResult.Loaded(it) }
.onErrorReturn { UserDataAppResult.Error(it.localizedMessage) }
.startWith(UserDataAppResult.InFlight)
.observeOn(AndroidSchedulers.mainThread())
.share()
fun createUser(): Flowable<CreateUserResult> {
val userId = UUID.randomUUID().toString()
val user = User()
user.id = userId
return appDatabase.userDao().insertAll(user)
.map <CreateUserResult> { CreateUserResult.Loaded(user) }
.onErrorReturn { CreateUserResult.Error(it.localizedMessage) }
.startWith(CreateUserResult.InFlight)
}
Currently UserDataAppResult.Error was not found, which makes sense. But is it possible to reuse the private AppResult class hierarchy and introduce new types.
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This is not possible in Kotlin. Every type you use must have an explicitly declared class. Classes are not implicitly created by the compiler even when nested classes are declared in a superclass.
For your problem, I recommend that you rewrite the code from combining two inheritance-based hierarchies into one of two combinations of inheritance and composition, or simply rebuild the hierarchy in some way, for example (I suppose the exact instance of the result will be irrelevant to you if this is not Loaded
):
sealed class AsyncResult {
object InFlight : AsyncResult()
data class Error(val errorMessage: String) : AsyncResult()
sealed class Loaded<out T>(val result: T) : AsyncResult() {
sealed class UserDataAppResult(users: List<User>) : Loaded<List<User>>(users)
sealed class CreateUserResult(user: User) : Loaded<User>(user)
}
}
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