abstract class Base
    interface Stackable
    class SubA : Base(), Stackable
    class SubB: Base()

    val things: List<Base> = listOf(SubA(), SubB())
    fun <T: Base> get(type: KClass<T>): T {
        return things.first { it::class == type } as T
    }
    fun <T: Stackable> get(type: KClass<T>): List<T> {
        return things.first { it::class == type } as List<T>
    }