What is the reason behind `objects` being frozen - technical limitation or a language concept? What ...

# announcements

[Andy Victors]

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?

[Marko Mitic]

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

[Andy Victors]

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

[Marko Mitic]

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

[Marko Mitic]

Notify me if this helps, I'm also interested in solution but I don't have time to allocate to this right now

[obobo]

What's preventing you from declaring the fields inside an object as var, or setting a mutable object (like a MutableList) as a field?

[Andy Victors]

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.

[Casey Brooks]

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

[obobo]

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.

[ilya.gorbunov]

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

[obobo]

Ah, I see, thanks.

[Andy Victors]

Any ideas why AtomicReference is not available for me? Kotlin '1.3.30'

[Marko Mitic]

Is it available on Native only?

[Andy Victors]

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

[Marko Mitic]

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

[Marko Mitic]

Not sure if that is the right way to go. Can somebody help? @ilya.gorbunov

[Andy Victors]

@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.