Kotlin Inheritance / Declaration with Generics

Question

I'm trying to initiate the RoomAlarmRepository inside the RepoInit 1 & 2.

The first one says "Type mismatch", and wouldn't let me compile. That is, unless I cast it like in RepoInit2, at which point it tells me that the cast is unchecked.

class RepoInit1(app: App) {
internal val repo: AlarmRepository<AlarmModel> = RoomAlarmRepository(app.database)
}

class RepoInit2(app: App) {
internal val repo: AlarmRepository<AlarmModel> = RoomAlarmRepository(app.database) as AlarmRepository<AlarmModel>
}


class RoomAlarmRepository(val database: AppDatabase) : AlarmRepository<RoomAlarmModel> {

}

class RoomAlarmModel : AlarmModel {


}

I'm currently using the second one, as it actually works. I know I'm missing something where I declare the variable, but I'm not sure what it is.

Rene · Accepted Answer · 2018-11-10 18:26:36Z

1

Declare the generic type it with the out modifier as covariant. See here https://kotlinlang.org/docs/reference/generics.html for details.

class RepoInit2(...) {
    internal val repo: AlarmRepository<out AlarmModel> = RoomAlarmRepository(...)
}

answered Nov 10, 2018 at 18:26

Rene

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