* currently planned to be released as a general-purpose forwarding class.
 *
 * @author James Sexton
 * @author Joshua O'Madadhain
 */
abstract class ForwardingNetwork<N, E> extends AbstractNetwork<N, E> {

  abstract Network<N, E> delegate();

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

  @Override
  public Set<E> edges() {

      return delegate().edgeValueOrDefault(transpose(endpoints), defaultValue);
    }
  }

  private static final class TransposedNetwork<N, E> extends ForwardingNetwork<N, E> {
    private final Network<N, E> network;

    TransposedNetwork(Network<N, E> network) {
      this.network = network;
    }

    @Override
    Network<N, E> delegate() {

      return delegate().edgeValueOrDefault(transpose(endpoints), defaultValue);
    }
  }

  private static final class TransposedNetwork<N, E> extends ForwardingNetwork<N, E> {
    private final Network<N, E> network;

    TransposedNetwork(Network<N, E> network) {
      this.network = network;
    }

    @Override
    Network<N, E> delegate() {