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I have encountered a puzzling issue where a *InvalidMutabilityException* is thrown when a function is invoked on a Object (not to be confused with a class object):
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Uncaught exception from Kotlin's main: kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen org.digieng.gobject_meta.NamespaceInfo@167e938
        at ThrowInvalidMutabilityException (0x2406f9)
        at  (0x24f4e6)
        at kfun:org.digieng.gobject_meta.NamespaceInfo.clearState#internal (0x258a00)
        at kfun:org.digieng.gobject_meta.NamespaceInfo.load(kotlin.String;kotlin.String) (0x256777)
        at Konan_start (0x21bac2)
        at Konan_run_start (0x21b870)
        at Konan_main (0x21b7a7)
        at __libc_start_main (0x7f15dd833f45)
        at  (0x21b029)
        at  ((nil))
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Why do you find it puzzling? Top level singleton objects are immutable after creation, so exception is thrown. 

Was expecting the behaviour of singleton objects on Kotlin Native to be the same as Kotlin JVM/JS. That is mutable properties on Objects (singleton classes) can be changed after being initialised.

Does a class have to be used instead in order to have mutable properties that aren't top level in a source file?

Is there a document that goes into detail on how Kotlin Native handles/approaches immutability?

<https://kotlinlang.org/docs/reference/native/immutability.html>

You could use @ThreadLocal annotation to have mutable top level objects

For a longer explanation on how threading works I wrote a set of blog posts: <https://medium.com/@kpgalligan/kotlin-native-stranger-threads-ep-1-1ccccdfe0c99>