public void appendAll(Provider<? extends Iterable<? extends T>> provider) {
        withActualValue(it -> it.addAll(provider));
    }

    @Override
    public int size() {
        return calculateOwnPresentValue().getWithoutSideEffect().size();
    }

    /**
     * Adds the given supplier as the new root supplier for this collection.
     *
     * @param collector the collector to add