We’ve done a simple test with serializations. We send a list to a rest endpoint which iterated through it. We compared serializing to

java.util.List

with

kotlin.collections.List

and were surprised to find that the Kotlin serialization took twice the time. The theory is that Jackson serializes to a Java list, and then Kotlin converts it to a Kotlin list. If that is true, then it would be worth the time experimenting with native Kotlin serializers.

There is no "kotlin list".

kotlin.collections.List

is

java.util.List

from a Java standpoint.

As Take mentioned, Kotlin List interface is just Java List on runtime and implemented by default by java's array list. So performance of lists is exactly the same and from point of view of Jackson there is no such thing as Kotlin list, most probably you have same problem in your benchmark