* @param <V> Value parameter type
 */
final class UndirectedGraphConnections<N, V> implements GraphConnections<N, V> {
  private final Map<N, V> adjacentNodeValues;

  private UndirectedGraphConnections(Map<N, V> adjacentNodeValues) {
    this.adjacentNodeValues = checkNotNull(adjacentNodeValues);
  }

  static <N, V> UndirectedGraphConnections<N, V> of(ElementOrder<N> incidentEdgeOrder) {

    return graph.isDirected()
        ? DirectedGraphConnections.ofImmutable(
            node, graph.incidentEdges(node), successorNodeToValueFn)
        : UndirectedGraphConnections.ofImmutable(
            Maps.asMap(graph.adjacentNodes(node), successorNodeToValueFn));
  }

  /**
   * A builder for creating {@link ImmutableValueGraph} instances, especially {@code static final}