Both OOP and type-classes are a form of ad-hoc polymorphism, but OOP is not a replacement for type-classes. The scope overlaps and personally I find both useful

Both OOP and type-classes are a form of ad-hoc polymorphism, but OOP is not a replacement for type-classes. The scope overlaps and personally I find both useful, but you're making the mistake to think that type-classes are about subtyping. They are not. Also, type-classes in Scala are not implemented by means of "implicit conversions". It has nothing to do with it. Type-classes in Scala are implemented by means of implicit parameters, also called context bounds, but that's different. Of course, you don't really need implicit parameters to work with type-classes. That's just syntactic sugar, because you can just pass dictionaries (type-class instances) around manually. No, the far bigger problem that Kotlin has is that it doesn't support higher-kinded types. Without higher-kinded types you can't express generic code for containers (e.g. M[T]). And without that, you can't do do type-classes and you can kiss most FP abstractions goodbye. If you don't believe me, try coming up with an interface for things that have "map", "filter" or "flatMap.