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What is the best way to deserialize a heterogenous array that looks like this in JSON? I can write a custom serializer, but I am stuck on which descriptor to use, because `listSerialDescriptor` assumes a homogenous array.
```[{"key": "value"}, "string"]```
In Swift, I can pull arbitrary types out of an `UnkeyedDecodingContainer` in any order I need

It seems like the best i can do is use polymorphic serialization for the entire array with a fixed set of subtypes and then runtime cast them, hoping that the object shapes are distinct enough to not be confused for one another

because I cannot use the position in the array as a hint to the serializer even though I know the types ahead of time

You could also maybe serialize it into JsonElements and write something to manually walk the tree… It’s definitely not ideal, but it lets you do stuff like use the positions in the list in some more manual serialization logic

<https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/json.md#json-elements>

I might have to do that because even Polymorphic does not work here – Polymorphic seems to assume JsonObject and not JsonElement

yeah, <https://github.com/Kotlin/kotlinx.serialization/blob/920f58979990bace9aaecd300e59bee89a4b0dec/formats/json/commonMain/src/kotlinx/serialization/json/internal/Polymorphic.kt#L62|https://github.com/Kotlin/kotlinx.serialization/blob/920f58979990bace9aaecd300e59b[…]mmonMain/src/kotlinx/serialization/json/internal/Polymorphic.kt>

it requires a discriminator, too, so only supports
“internal tagging” in <http://serde.rs|serde.rs> parlance

there is Json.useArrayPolymorphism but that isn't what you want either

you'll have to write a custom serializer, it doesn't have to be too hard if you use `ListSerializer(JsonElement.serializer())` (or equivalents) as a <https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/serializers.md#composite-serializer-via-surrogate|surrogate>. It won't work for any format other than JSON, but this kind of structure also doesn't work with other formats so you're not really losing anything

Yep, totally. JsonElement ended up working pretty well!