fun interface Observer<T> {
    fun onChange(t: T)
}

sealed class TaskState<out T> {
    class Initial<out T>(val d: T) : TaskState<T>()
}

class Container<T>(val t: T)

class ViewModel {
    sealed class AvailableTask<out T> {
        object AvailableTask1 : AvailableTask<Boolean>()
        object AvailableTask2 : AvailableTask<Boolean>()
    }

    val taskState: Container<TaskState<Boolean>> = Container(TaskState.Initial(false))

    fun <T> foo(
        availableTask: AvailableTask<T>,
        obs: Observer<TaskState<T>>
    ) {
        val concreteTaskState = when (availableTask) {
            is AvailableTask.AvailableTask1 -> taskState
            is AvailableTask.AvailableTask2 -> taskState
            else -> taskState
        }

        /**
         * Lint error:
         * Required: TaskState<T>
         * Found: TaskState<Boolean>
         */
        obs.onChange(concreteTaskState.t)
    }
}

val v = ViewModel()
v.foo(ViewModel.AvailableTask.AvailableTask1) { taskState: TaskState<Boolean> ->

}