What do you mean by inability to represent existential types? Kotlin has in/out/star projections, which are be used for corresponding Java variance. A note about Scala interop: forget the existential types, in Scala I cannot simply use interfaces with bounded type parameters without some dirty hacks, just because compiler will generate weird errors and/or incorrect bytecode. I am sorry, but this makes it just impossible to work with Java in Scala.
The whole point of Kotlin is that it does not need its own ecosystem - it is intended to be used seamlessly (unlike Scala or Ceylon) and, like, today with all existing Java libraries and frameworks. Sure, more idiomatic solutions would always be nicer to work with (and they would probably appear at some time), but you do not need to wait for them - just go with your existing codebase.
As for the tooling, Kotlin IDE support way better than Scala's. It is not surprising, however, due to the fact that main language kontributors are JetBrains.
> What do you mean by inability to represent existential types? Kotlin has in/out/star projections, which are be used for corresponding Java variance
Hmm ok, that does seem to provide equivalent functionality. Is it implemented?
> in Scala I cannot simply use interfaces with bounded type parameters without some dirty hacks, just because compiler will generate weird errors and/or incorrect bytecode
Example? I've never seen that happen and I've done a fair bit of mixed Java/Scala.
> The whole point of Kotlin is that it does not need its own ecosystem - it is intended to be used seamlessly (unlike Scala or Ceylon) and, like, today with all existing Java libraries and frameworks.
Scala was intended for that at first. It turned out to be a bad approach. Interfaces are important, library APIs have a surprisingly far-reaching impact on the code that calls them.
> As for the tooling, Kotlin IDE support way better than Scala's. It is not surprising, however, due to the fact that main language kontributors are JetBrains.
That one specific tool perhaps. In terms of the much larger ecosystem of third-party JVM tools, Scala support is naturally more mature.
The whole point of Kotlin is that it does not need its own ecosystem - it is intended to be used seamlessly (unlike Scala or Ceylon) and, like, today with all existing Java libraries and frameworks. Sure, more idiomatic solutions would always be nicer to work with (and they would probably appear at some time), but you do not need to wait for them - just go with your existing codebase. As for the tooling, Kotlin IDE support way better than Scala's. It is not surprising, however, due to the fact that main language kontributors are JetBrains.