What is the reason behind

objects

being frozen - technical limitation or a language concept? What us then the alternative of keeping the global modifiable list of, say, users in the app?

Frozen objects are immutable, immutable objects are thread-safe, thread-safe objects remove multi-threading bugs

I see the logic here, but how do I implement [mutable] singleton multithreaded component in Kotlin?

AtomicReference? https://medium.com/@kpgalligan/kotlin-native-stranger-threads-ep-2-208523d63c8f

What's preventing you from declaring the fields inside an object as

var

, or setting a mutable object (like a

MutableList

) as a field?

Hm.. just checked - I have my mutable list declared inside the object like

private val fetchers: ArrayList<DataSourceFetcher> = ArrayList()

. Will try the same using `var`and report.

Once an object is frozen, all its children objects are also frozen. The only way to have mutable properties in an

object

for mutable singletons is to use

AtomicReference

or other atomic data structures. I was fighting this a while ago and that really is the only route, unfortunately

Oh, is this a KotlinJS or Android thing? Because JVM objects are just singletons. I just tested out some code with a mutableList field in an object.

@alan.kleiman This is a Kotlin/Native memory model restriction

Ah, I see, thanks.

Any ideas why

AtomicReference

is not available for me? Kotlin '1.3.30'

Is it available on Native only?

According to documentation - it should be in both Common and Native.

There's atomicfu that should have multiplaform atomic ops https://github.com/Kotlin/kotlinx.atomicfu

@Casey Brooks

Once an object is frozen, all its children objects are also frozen.

Is there any option to distinguish between real children (owned) and referenced objects? Currently if I pass some object in constructor to the frozen object, that one is also get frozen which is not what I want.