Multiset<? extends E> multiset) {
    if (multiset instanceof UnmodifiableMultiset || multiset instanceof ImmutableMultiset) {
      @SuppressWarnings("unchecked") // Since it's unmodifiable, the covariant cast is safe
      Multiset<E> result = (Multiset<E>) multiset;
      return result;
    }
    return new UnmodifiableMultiset<>(checkNotNull(multiset));
  }

  /**
   * Simply returns its argument.

      Multiset<? extends E> multiset) {
    if (multiset instanceof UnmodifiableMultiset || multiset instanceof ImmutableMultiset) {
      @SuppressWarnings("unchecked") // Since it's unmodifiable, the covariant cast is safe
      Multiset<E> result = (Multiset<E>) multiset;
      return result;
    }
    return new UnmodifiableMultiset<>(checkNotNull(multiset));
  }

  /**
   * Simply returns its argument.

        checkNotNull(cell.getRowKey(), "row");
        checkNotNull(cell.getColumnKey(), "column");
        checkNotNull(cell.getValue(), "value");
        @SuppressWarnings("unchecked") // all supported methods are covariant
        Cell<R, C, V> immutableCell = (Cell<R, C, V>) cell;
        cells.add(immutableCell);
      } else {
        put(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
      }
      return this;

        checkNotNull(entry.getKey());
        checkNotNull(entry.getValue());
      }
      @SuppressWarnings({"unchecked", "rawtypes"})
      // immutable collections are safe for covariant casts
      // and getting the generics right for EnumMap is difficult to impossible
      ImmutableMap<K, V> result = ImmutableEnumMap.asImmutable(new EnumMap(enumMap));
      return result;
    }

        checkNotNull(cell.getRowKey(), "row");
        checkNotNull(cell.getColumnKey(), "column");
        checkNotNull(cell.getValue(), "value");
        @SuppressWarnings("unchecked") // all supported methods are covariant
        Cell<R, C, V> immutableCell = (Cell<R, C, V>) cell;
        cells.add(immutableCell);
      } else {
        put(cell.getRowKey(), cell.getColumnKey(), cell.getValue());
      }
      return this;

   */
  public static <E> ImmutableList<E> copyOf(Collection<? extends E> elements) {
    if (elements instanceof ImmutableCollection) {
      @SuppressWarnings("unchecked") // all supported methods are covariant
      ImmutableList<E> list = ((ImmutableCollection<E>) elements).asList();
      return list.isPartialView() ? asImmutableList(list.toArray()) : list;
    }
    return construct(elements.toArray());
  }

 * href="https://github.com/google/guava/wiki/UsingAndAvoidingNullExplained#optional">using {@code
 * Optional}</a>.
 *
 * @param <T> the type of instance that can be contained. {@code Optional} is naturally covariant on
 *     this type, so it is safe to cast an {@code Optional<T>} to {@code Optional<S>} for any
 *     supertype {@code S} of {@code T}.
 * @author Kurt Alfred Kluever
 * @author Kevin Bourrillion
 * @since 10.0
 */

 * href="https://github.com/google/guava/wiki/UsingAndAvoidingNullExplained#optional">using {@code
 * Optional}</a>.
 *
 * @param <T> the type of instance that can be contained. {@code Optional} is naturally covariant on
 *     this type, so it is safe to cast an {@code Optional<T>} to {@code Optional<S>} for any
 *     supertype {@code S} of {@code T}.
 * @author Kurt Alfred Kluever
 * @author Kevin Bourrillion
 * @since 10.0
 */

       * ...> or ImmutableEnumMap<K, ...> along the way because our own <K> isn't <K extends
       * Enum<K>>.
       *
       * We are also performing a covariant cast, potentially from ImmutableMap<K, Sub> to
       * ImmutableMap<K, Super>. That is safe because no one can add elements to the map.
       */
      @SuppressWarnings("unchecked")

    // Don't refer to ImmutableSortedSet by name so it won't pull in all that code
    if (elements instanceof ImmutableSet && !(elements instanceof SortedSet)) {
      @SuppressWarnings("unchecked") // all supported methods are covariant
      ImmutableSet<E> set = (ImmutableSet<E>) elements;
      if (!set.isPartialView()) {
        return set;
      }
    }
    Object[] array = elements.toArray();
    return construct(array.length, array);