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kotlinlang

I appear to be confused about snapshot state. The following code crashes with a ConcurrentModificationException, presumably when the source SnapshotStateList is modified while sorting in `derivedStateOf`.

```private val list = mutableStateListOf&lt;Thing&gt;()

val sortedList by derivedStateOf {
    list.sorted()
}```

Do I need to be protecting against modifications to the state I read in `derivedStateOf` blocks?

I see now that `toList()` is intended to be used to get the PersistentList for the current snapshot record, so you can iterate without dealing with concurrent modifications. It's a bit concerning that using standard Kotlin library functions such as `map`, `fold`, `filter`, etc. run the risk of crashing unless this is used. Would it make sense to have `iterator()` return `toList().iterator()` instead of the SnapshotStateList's `ListIterator` implementation?

Ah, that wouldn't work because of the `MutableList` interface's contract that `iterator()` returns a `MutableIterator`. Feels like a footgun inherited by Java.

List.sorted doesnt realy make sense for derived state &amp; snapshot state list because you are modifying the snapshot state list *while its trying to run the derived block*.

You need List.sort() which creates a new list that is sorted from the first one.

That's backward, MutableList.sort is the in-place version

Oh woops, my bad, then something is wrong somewhere

Yeah, it's because I need to call `list.toList()` to get the underlying immutable list for the snapshot

Yeah I use the `toList()` version everywhere (i also have a derived sorted list too) so I haven’t run into this. But I agree it should be somewhat clarified

This seems like a bug to me… if sorted doesn’t mutate the underlying list. Can you file?

I'm reporting now, but as I'm writing this it strikes me that it's not really a problem with Compose, but more of a problem with the List/MutableList interface.

Like, this would happen if it were a `MutableList` instead of a `SnapshotStateList`.

<https://issuetracker.google.com/issues/272334463>