kotlin override property from interface with subtype

Question

I have the following situation:

interface AbstractState {...}
interface SubState {...}

interface NiceInterface {
  var currentState: AbstractState
  ...
}

Furthermore I have a class which implements this interface.

class Class : NiceInterface {
  override var currentState: AbstractState = SubState()
}

This implies that I have to write the following at every use of it in the class:

(currentState as SubState).doSomething()

Is there a way to avoid the "as SubState" part? Or some kind of smart way to do it?

Like with generics:

interface => val currentStates: List<out AbstractState>
class     => override val currentStates = ArrayList<SubState>()

Related: https://stackoverflow.com/questions/2701182/call-a-method-of-subclass-in-java — user202729, Aug 01 '18 at 07:15
(tl;dr. the top answer there says that you're doing something wrong) — user202729, Aug 01 '18 at 07:15

score 1 · Answer 1 · answered Sep 28 '19 at 10:47

As Alexey Romanov said the problem with setter, so there is a workaround, replace var by val:

interface AbstractState {}
class SubState : AbstractState{}

interface NiceInterface {
    val currentState: AbstractState
}

class Class : NiceInterface {
    override val currentState: SubState by lazy {
        SubState()
    }
}

So now you don't need to cast:

currentState.doSomething()

kotlin override property from interface with subtype

1 Answers1