Base class for slots. std::vector<implementation-detail> bool true if any tracked object has expired. locked_container_type A container holding shared_ptrs to each of the slot's tracked objects. As long as the returned container is kept in scope, none of the slot's tracked objects can expire. expired_slot if any of the slot's tracked objects have expired. bad_weak_ptr Indicates at least one of a slot's tracked objects has expired. The expired_slot exception is thrown to indicate at least one of a slot's tracked objects has expired. const char *