Go has a similar feature, and while I don't know that I would say it's especially controversial or frowned upon, it's good form to only use it sparingly if at all. I still wouldn't say that it is anywhere near as fragile as inheritance; however--I think inheritance's fragility comes from its polymorphism (not sure about Kotlin, but in Go, the wrapper class/struct can't be passed into a function that expects the component's type).