The Kotlin runtime will add a little to your app size, adding around 1MB. The performance in simple terms would be the same, because both languages can be compiled down to the same byte codes. However, co-routines (finalised at the end of last year) allow you to use threads much more efficiently by writing your code in a different style. Therefore, you can more easily write code that will make use of CPU resources that would otherwise be blocked.
(Check out the appendix in Head First Kotlin where we write a drum machine on a single thread with coroutines...)
Thanks for the question
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