In general Java it's still messy because although you can make the value of a variable immutable, the innards of the object it's holding are still mutable. Such

In general Java it's still messy because although you can make the value of a variable immutable, the innards of the object it's holding are still mutable. Such as appending to a list. You have to go as far as Clojure does and create a whole new suite of truly immutable data containers, for full safety. I dunno if Kotlin goes this far. But yeah, it's the right way.