Method copyOf

corpus/java/training/guava/collect/ImmutableSet.java:232–248

Returns an immutable set containing each of elements, minus duplicates, in the order each appears first in the source collection. Performance note: This method will sometimes recognize that the actual copy operation is unnecessary; for example, copyOf(copyOf(anArrayList))

(Collection<? extends E> elements)

   * @since 7.0 (source-compatible since 2.0)
   */
  public static <E> ImmutableSet<E> copyOf(Collection<? extends E> elements) {
    /*
     * TODO(lowasser): consider checking for ImmutableAsList here
     * TODO(lowasser): consider checking for Multiset here
     */
    if (elements instanceof ImmutableSet && !(elements instanceof ImmutableSortedSet)) {
      @SuppressWarnings("unchecked") // all supported methods are covariant
      ImmutableSet<E> set = (ImmutableSet<E>) elements;
      if (!set.isPartialView()) {
        return set;
      }
    } else if (elements instanceof EnumSet) {
      return copyOfEnumSet((EnumSet) elements);
    }
    Object[] array = elements.toArray();
    return construct(array.length, array);
  }

  /**
   * Returns an immutable set containing each of {@code elements}, minus duplicates, in the order