Component.kt

interface Component {
   val children: Iterable<Component>
   fun requestFocus()
   fun clearFocus()
}

class MyComponent(
       override val children: Iterable<Component>,
       val drawSurface: DrawSurface) : Component {

   override fun requestFocus() {
   }

   override fun clearFocus() {
   }

   fun render() {
   }

   fun attachTo(container: Container) {
   }
}