is there a kotlin native way to have a `SortedMap`...

# kotlin-native

[Rohde Fischer]

is there a kotlin native way to have a SortedMap? E.g., when I'm deserializing a json map where the order is important 🙂 It seems that Map happens to be sorted, but I assume it's the same as for Java - there is no guarantee it will stay that way, am I correct in that assumption? If so what can/should I do?

[ephemient]

I am not sure which behavior you are talking about

[ephemient]

Kotlin/JVM has a .toSortedMap() extension function, which returns a java.util.SortedMap. this is a map whose keys are always iterated in comparator order. this is not available on Kotlin/Native

[ephemient]

most of the Map-returning functions in Kotlin stdlib return an order-preserving map: entries are iterated in insertion order (kotlin.collections.HashMap being an exception and explicitly guaranteeing no particular order)

[ephemient]

do you actually want a SortedMap, e.g.

mapOf("b" to 1, "a" to 2).toSortedMap().entries.toList() // [a=2, b=1]

or do you want an order-preserving map, e.g.

mapOf("b" to 1, "a" to 2).entries.toList() // [b=1, a=2]

[ephemient]

if you are using kotlinx.serialization, the default Map deserialization uses LinkedHashMap, which preserves order

[Rohde Fischer]

good point, I see the difference. What I want is an order preserving map indeed 🙂 and I am using kotlinx.serialization, so sounds like I'm well off already 🙂 can I trust that it will stay an order preserving map (would make sense to me, but some times there are reasons 😉 )?

[ephemient]

I would expect so - that is the behavior of all standard maps across all of Kotlin, and I would consider a change to that to be breaking - but it doesn't appear to be documented in kotlinx.serialization

[Michael Paus]

It is documented here for example: https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/mutable-map-of.html

The returned map preserves the entry iteration order.

[Rohde Fischer]

nice, thanks 🙂

[ephemient]

right, it's documented on the Kotlin stdlib side, but there's nothing in the kotlinx.serialization documentation (as far as I can see) that states that it's using that when decoding JSON

[Michael Paus]

But it would be strange if not, wouldn’t it?

[Rohde Fischer]

@Michael Paus it would, but it's programming, I mean I've seen people do some weird things