Method removeOnlySortedSet

guava/src/com/google/common/collect/Maps.java:1130–1163

(SortedSet<E> set)

  }

  private static <E extends @Nullable Object> SortedSet<E> removeOnlySortedSet(SortedSet<E> set) {
    return new ForwardingSortedSet<E>() {
      @Override
      protected SortedSet<E> delegate() {
        return set;
      }

      @Override
      public boolean add(@ParametricNullness E element) {
        throw new UnsupportedOperationException();
      }

      @Override
      public boolean addAll(Collection<? extends E> es) {
        throw new UnsupportedOperationException();
      }

      @Override
      public SortedSet<E> headSet(@ParametricNullness E toElement) {
        return removeOnlySortedSet(super.headSet(toElement));
      }

      @Override
      public SortedSet<E> subSet(
          @ParametricNullness E fromElement, @ParametricNullness E toElement) {
        return removeOnlySortedSet(super.subSet(fromElement, toElement));
      }

      @Override
      public SortedSet<E> tailSet(@ParametricNullness E fromElement) {
        return removeOnlySortedSet(super.tailSet(fromElement));
      }
    };
  }

  @GwtIncompatible // NavigableSet
  private static <E extends @Nullable Object> NavigableSet<E> removeOnlyNavigableSet(