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kotlinlang

how can I sort a `Map`? alternatively, is there a sorted map type other than `TreeMap` (because that one is a Java thing and gives me platform types)

Could you please explain a bit the use case / context for why you need a sorted map?

I ended up just implementing a flatmap into a list, which is then sorted.

Yes, usually maps are data structures meant for lookup, not iteration. So depending on the use case you can derive a list from it

yep. forcing a map to be sorted at all times is not what I want or need in this case (or in most cases, probably)

why can't you simply do `yourMap.toSortedMap().forEach(...)`?

why flatmap? I'd expect
```.entries.sortedBy { it.key }
```
to give you what you want

What exactly could you do if `TreeMap` was a Kotlin type that you can't do because it's a Java type?

nothing, this is just me making assumptions that Kotlin implementations are somehow preferred. which doesn't actually seem to be true in many cases.

re: flatmap - you're correct. I had to flatmap because the value of my map was more complex, and I forgot to mention this.

treemap's platform types in Kotlin aren't great, and its performance relative to hashmap isn't great in Java either, so I can understand wanting an alternative

Yeah `TreeMap` is actually most useful when you want to read or remove subtrees based on the sorting of the keys, like "give me the subtree of all keys below 42". If you just want sorted iteration, it's most likely better to just iterate on the sorted entries in the places where you need that.

Talking of platform types, I'm confused: `TreeMap` seems to behave as if Kotlin knows its nullability requirements, so the following doesn't compile:
```java.util.TreeMap&lt;String, String&gt;().put(null as String?, "")```
On the other hand, various other Java types that also require an argument to be non-null, do in fact compile:
```java.io.FileOutputStream(null as java.io.File?)```

might be relevant: <https://kotlinlang.slack.com/archives/C0B8MA7FA/p1674490254501389?thread_ts=1674480790.422839&amp;cid=C0B8MA7FA>

(please ignore the fact that I re-asked the same question :disappointed: )