Generic extending class AND implements interface in Kotlin
Solution 1:
Only one upper bound can be specified inside the angle brackets.
Kotlin offers different syntax for generic constraints when there is more than one constraint:
class Foo<T>(val t: T) where T : Bar, T : Baz { ... }
and for functions:
fun <T> f(): Foo where T : Bar, T : Baz { ... }
It is documented here.