Readme.md

Views

In many cases, rather than copy the memory of an object, we just need an alternative view of it (like another way to iterate through the collection).

For example, the ImmutableSet check if the elements actually is another ImmutableSet; if yes, just create another View of the same object.

// see https://guava.dev/releases/snapshot/api/docs/src-html/com/google/common/collect/ImmutableSet.html#line.218
public static <E> ImmutableSet<E> copyOf(Collection<? extends E> elements) {
  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;  // Another View!
    }
  } else if (elements instanceof EnumSet) {
    return copyOfEnumSet((EnumSet) elements);
  }
  Object[] array = elements.toArray();
  if (elements instanceof Set) {
    // assume probably no duplicates (though it might be using different equality semantics)
    return construct(array.length, array.length, array);
  } else {
    return constructUnknownDuplication(array.length, array);
  }
}