Take a look at Gosu. It provides:

  - Reification
  - Declaration-site generics
  - Default covariance when variance not specified
  - Variance inference!

In practice default covariance is usually the most suitable; it's the pragmatic approach. But you can make a generic type super sound, if that's what you need. And with variance inference your generic type can safely inherit from generic Java types.

http://gosu-lang.github.io/2015/11/22/threading-the-needle.h...

Is there a reason to take a look at Gosu instead of Kotlin?

You mean aside from it providing better and easier generics support? I personally like Kotlin, but I think Gosu has some advantages that should not be overlooked e.g,. Generics support.

The problem with Gosu is that it never gained any significant traction.