code: @CanIgnoreReturnValue
    public static <T> boolean addAll(Collection<T> addTo, Iterable<? extends T> elementsToAdd) {
      if (elementsToAdd instanceof Collection) {
        Collection<? extends T> c = Collections2.cast(elementsToAdd);
        return addTo.addAll(c);
      }
      return Iterators.addAll(addTo, checkNotNull(elementsToAdd).iterator());
    }
docs: Adds all elements in {@code iterable} to {@code collection}.
  
  @return {@code true} if {@code collection} was modified as a result of this operation.