Which features attract you to use Kotlin?

closures like in functional languages, native compiler, tail call optimisation

Shared code between jvm and ios (combination of performance and ease of use).

The ability to declare functions outside of classes. I mean come on Java

Honestly my favorite "feature" is that i seem to find myself thinking "oh man i have to do X small yet annoying thing" just to find out "oh no i don't, theres an ext function for that!" Also TornadoFX is fun.

that its not java and can be used in the same places

the combination of extension functions, ext functs with receiver, lambdas, and what i thought was a weird feature of putting the last function parameter on the outside of the

()

inside of

{}

instead ...that come together to make the various DSLs is quite nice.

yeah i still find that one odd

It's one of those things that sounds really arbitrary and useless until you see it in action. So if you've used .apply {} or .let {} or any of the DSLs like tornadofx or ktor it starts to click.

combine that with extension functions with receiver object inside your DSL objects/class and you get the power of the DSL, you can quite possibly model any arbitrarir nested configuration in a typesafe and readable way

yeah only starting to do stuff with a DSL now

But kotlin need remember more things then java.

do you mean when writing kotlin or the kotlin compiler ?

data class, null safety, less verbose code