* A class to allow {@link Graph} implementations to be backed by a {@link BaseGraph}. This is not
 * currently planned to be released as a general-purpose forwarding class.
 *
 * @author James Sexton
 */
abstract class ForwardingGraph<N> extends AbstractGraph<N> {

  abstract BaseGraph<N> delegate();

  @Override
  public Set<N> nodes() {
    return delegate().nodes();
  }

  /**

 * which is in O(d_node) where d_node is the degree of {@code node}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 */
final class StandardMutableGraph<N> extends ForwardingGraph<N> implements MutableGraph<N> {
  private final MutableValueGraph<N, Presence> backingValueGraph;

  /** Constructs a {@link MutableGraph} with the properties specified in {@code builder}. */

 * which is in O(d_node) where d_node is the degree of {@code node}.
 *
 * @author James Sexton
 * @param <N> Node parameter type
 */
final class StandardMutableGraph<N> extends ForwardingGraph<N> implements MutableGraph<N> {
  private final MutableValueGraph<N, Presence> backingValueGraph;

  /** Constructs a {@link MutableGraph} with the properties specified in {@code builder}. */

  // NOTE: this should work as long as the delegate graph's implementation of edges() (like that of
  // AbstractGraph) derives its behavior from calling successors().
  private static final class TransposedGraph<N> extends ForwardingGraph<N> {
    private final Graph<N> graph;

    TransposedGraph(Graph<N> graph) {
      this.graph = graph;
    }

    @Override
    Graph<N> delegate() {
      return graph;
    }

  // NOTE: this should work as long as the delegate graph's implementation of edges() (like that of
  // AbstractGraph) derives its behavior from calling successors().
  private static final class TransposedGraph<N> extends ForwardingGraph<N> {
    private final Graph<N> graph;

    TransposedGraph(Graph<N> graph) {
      this.graph = graph;
    }

    @Override
    Graph<N> delegate() {
      return graph;
    }