open class Parent {
  fun load() {
    return ... // don't know what to return here
  }
}

class ChildA : Parent () {
  fun methodA() = ...
}

class ChildB : Parent () {
  fun methodB() = ...
}

class Usage {
  fun fooA() {
    ChildA().load().methodA() // I want to achieve this chaining
  }

  fun fooA() {
    ChildB().load().methodB()
  }
}

abstract class Parent<T : Parent<T>> {
    abstract fun load(): T
}

class ChildA : Parent<ChildA> () {
    override fun load(): ChildA = TODO()

    fun methodA(): Int = TODO()
}

class ChildB : Parent<ChildB> () {
    override fun load(): ChildB = TODO()

    fun methodB(): Int = TODO()
}

class Usage {
    fun fooA() {
        ChildA().load().methodA()
    }

    fun fooB() {
        ChildB().load().methodB()
    }
}