I have this Repository class in the `commonMain`: ...

# kotlin-native

[Daniele B]

I have this Repository class in the `commonMain`:

class Repository {
    companion object Data {
        var lastUpdate: String? = null
        var countriesListWithSummary: List<CountrySummary> = emptyList()
    }
}

when I compile it for iOS, I get these warnings:
Variable in singleton without @ThreadLocal can't be changed after initialization

and on runtime I actually get this crash:
kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen mypackage.Repository.Data@3310e88

How should I handle this situation?

[aleksey.tomin]

val lastUpdate: AtominRef<String?> = AtominRef(null)
        val countriesListWithSummary: AtominRef<List<CountrySummary>> = AtominRef(emptyList())

…

countriesListWithSummary.value = someList.freeze()

[louiscad]

@Daniele B You need to decide whether you want it to be thread local, and in this case annotate it with @ThreadLocal, and only mutate it from the same thread (e.g. the main thread), or you need to have it immutable (the default, that can be made explicit with @SharedImmutable, at which point it wouldn't make sense to have a var, or, if you really need to have it mutable from multiple threads, you can use an atomic reference as Alexey Tomin is suggesting with his snippet.

[Daniele B]

I am actually going to modify them only from Dispatchers.Main

[louiscad]

Then use @ThreadLocal

[Daniele B]

so can @ThreadLocal be ok for that?

[louiscad]

As the compiler is suggesting

[louiscad]

yes, it will be local to the main thread

[Daniele B]

what about if there are concurrent coroutines on Dispatchers.Main ?

[aleksey.tomin]

@ThreadLocal variable has different states for each thread - isn’t it?

[aleksey.tomin]

Dispatchers.Main thread set some state but another thread will be read initial state 🙂

[louiscad]

@Daniele B It's no problem, just don't do the following:
Reading the value, run suspending code and updating the value base on what you've read.

[Daniele B]

@louiscad it seems ok then! many thanks