Sorry. This is off-topic. It really has nothing to...

# language-proposals

[elizarov]

Sorry. This is off-topic. It really has nothing to do with Kotlin. Designing parametrized type hierarchies is non trivial in any language. There is no difference between Java and Kotlin in this respect. You just have to make sure that the types in all the methods are properly specified and all the classes have all the type parameters with appropriate bounds.