Does kotlin native currently not support hash codes changing throughout the lifecycle of a class for...

# kotlin-native

[Todd]

Does kotlin native currently not support hash codes changing throughout the lifecycle of a class for data classes?
Details in 🧵

[Todd]

I have a data class

private data class Point(
    var x: Int,
    var y: Int
)

that I am modifying and then inserting into a hashSet. However when I do this I get an error:

kotlin.IllegalStateException: This cannot happen with fixed magic multiplier and grow-only hash array. Have object hashCodes changed?
	at kotlin.Throwable#<init>(/opt/buildAgent/work/5f69639f351c4725/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/Throwable.kt:25)
	at kotlin.Exception#<init>(/opt/buildAgent/work/5f69639f351c4725/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/Exceptions.kt:23)
	at kotlin.RuntimeException#<init>(/opt/buildAgent/work/5f69639f351c4725/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/Exceptions.kt:34)
	at kotlin.IllegalStateException#<init>(/opt/buildAgent/work/5f69639f351c4725/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/Exceptions.kt:70)
	at kotlin.collections.HashMap.rehash#internal(/opt/buildAgent/work/5f69639f351c4725/kotlin/libraries/stdlib/native-wasm/src/kotlin/collections/HashMap.kt:239)
	at kotlin.collections.HashMap.ensureCapacity#internal(/opt/buildAgent/work/5f69639f351c4725/kotlin/libraries/stdlib/native-wasm/src/kotlin/collections/HashMap.kt:193)
	at kotlin.collections.HashMap.ensureExtraCapacity#internal(/opt/buildAgent/work/5f69639f351c4725/kotlin/libraries/stdlib/native-wasm/src/kotlin/collections/HashMap.kt:181)
	at kotlin.collections.HashMap#addKey(/opt/buildAgent/work/5f69639f351c4725/kotlin/libraries/stdlib/native-wasm/src/kotlin/collections/HashMap.kt:292)
	at kotlin.collections.HashSet#add(/opt/buildAgent/work/5f69639f351c4725/kotlin/libraries/stdlib/native-wasm/src/kotlin/collections/HashSet.kt:34)

I tried this on jvm and it seems to work fine. Also just copying the object before putting it in the set fixes the issue as well.

[Todd]

Maybe it’s something about inserting the object into the set, mutating the object and then inserting it into the set again

[Todd]

Or wait, it’s probably just because I’m modifying the object after putting into the set. I wonder why the jvm doesn’t have an issue with this. I wonder if it creates a copy.

[ephemient]

this causes problems on JVM as well, it just doesn't have the same check

[ephemient]

https://docs.oracle.com/javase/8/docs/api/java/util/Set.html

Note: Great care must be exercised if mutable objects are used as set elements. The behavior of a set is not specified if the value of an object is changed in a manner that affects equals comparisons while the object is an element in the set.

[Todd]

Ahh makes sense. Thank you!!

[vsazel]

It would be better not to have mutable properties in data class at all. Make changes by copying copy() into new instance.

[Todd]

I 100% agree with you. I was more just curious about the behavior when it comes to having mutable structures in set.