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kotlinlang

Kotlin has a `Map/MutableMap` which is a `LinkedHashMap` which preserves the insertion order unlike `HashMap`. In Java/Android, if one is used to using `HashMap` then I would think I can continue using `Map/MutableMap` in Kotlin. Is that correct?

Yes, both `LinkedHashMap` and `HashMap` implement `MutableMap`, which extends `Map`.

Thanks. In that case, I will use `LinkedHashMap`. Although I don't think I need to maintain order but I might as well use it.

If you don't need order, you should use HashMap, it uses less memory than Linked

I'm annoyed that `LinkedHashSet` is the default, now everybody is paying this cost all over the code and you need to actively think about using `hashSetOf` instead of `setOf`.

I assume the performance cost of LinkedHashMap versus HashMap is completely negligible in 99.9% of all cases.
IMHO one should not even think about such micro (nano?) optimizations, but rather spend that effort towards cleaner code with better overall organization.

Is there no difference between `linkedMapOf(1 to "z")` and `mapOf(1 to "z")`?

Or is `LinkedHashMap` a Java class whereas `Map` is Kotlin class, if there is such a thing, and by extension I should use Kotlin specific classes where ever possible.

`linkedMapOf` always returns a `LinkedHashMap`, `mapOf` returns different types for an empty map. Also ´linkedMapOf` is mutable.

But it's a strange situation, sometimes I use `linkedMapOf` to emphasize that the order matters because `mutableMapOf` clearly doesn't signal that.

&gt;`mapOf` returns different types for an empty map.
What do you mean by different types?

```
println(mapOf&lt;String, Int&gt;()::class)
println(mapOf&lt;String, Int&gt;("a" to 0)::class)
println(mapOf&lt;String, Int&gt;("a" to 0, "b" to 1)::class)
println(mapOf&lt;String, Int&gt;("a" to 0, "b" to 1, "c" to 2)::class)

//prints:
//kotlin.collections.EmptyMap
//java.util.Collections$SingletonMap
//java.util.LinkedHashMap
//java.util.LinkedHashMap
```