Kotlin extension function with Generic doesn't work with Any?

Question

I want to have an extension function from the RealmList class:

private inline fun RealmList<Any?>.saveAll() {
    this.forEach {
        item -> Realm.getDefaultInstance().insert(item!! as RealmModel)
    }
}

But whenever I use it, this error appears:

It's because of "covariance". `RealmList` is not a `RealmList` (in the latter you could put an `Int`, for instance) — user2340612, Jun 21 '18 at 09:57
Omg. Don't call `Realm.getDefaultInstance()` like that. You have to pair every getInstance() call with a close() call, it's in the docs — EpicPandaForce, Jun 21 '18 at 10:54

score 3 · Accepted Answer · answered Jun 21 '18 at 09:59

3

To achieve that add out to generic declaration of your extension function. It would work if such declaration was stated in the RealmList

private inline fun RealmList<out Any?>.saveAll() {
    this.forEach {
        item -> Realm.getDefaultInstance().insert(item!! as RealmModel)
    }
}

answered Jun 21 '18 at 09:59

Demigod

5,073
3
31
49

Omg. Don't call `Realm.getDefaultInstance()` like that. You have to pair every getInstance() call with a close() call, it's in the docs – EpicPandaForce Jun 21 '18 at 10:54

EpicPandaForce · Answer 2 · 2018-06-21T23:16:04.950

Your code is generally unsafe. Please fix your code, read the documentation, stuff like that.

Also, RealmList expects ? extends RealmModel, so you need to use T: RealmModel with out.

fun <T: RealmModel> RealmList<out T?>.saveAll() {
    Realm.getDefaultInstance().use { realm ->
        val wasInTransaction = realm.isInTransaction()
        try {
            if(!wasInTransaction) {
                realm.beginTransaction()
            }
            this.forEach {
                item -> item?.let { realm.insert(it) }
            }
            if(!wasInTransaction) {
                realm.commitTransaction()
            }
        } catch(e: Throwable) {
            if(realm.isInTransaction()) {
                realm.cancelTransaction()
            }
        }
    }
}

Downvote, huh. Well, I'll see you around when you get `mmap failed(): out of memory size: 1048576 offset: 3145728` — EpicPandaForce, Jun 22 '18 at 14:18

score -1 · Answer 3 · answered Jun 21 '18 at 10:14

-1

Maybe you should use Realms method to insert instead of performing your loop? That way your extension becomes a simple call:

fun <T: RealmModel> RealmList<out T?>.saveAll() = Realm.getDefaultInstance().insert(this)

answered Jun 21 '18 at 10:14

Pawel

15,548
3
36
36

Omg. Don't call `Realm.getDefaultInstance()` like that. You have to pair every getInstance() call with a close() call, it's in the docs – EpicPandaForce Jun 21 '18 at 10:53
I just wrote that off top of my head, I still think this is weird since insert should be wrapped within a transaction. – Pawel Jun 21 '18 at 11:59

Kotlin extension function with Generic doesn't work with Any?

3 Answers3