graph: use iterators directly rather than copying into []graph.Node

There are still uses in test code; these can remain since they simplify
that code.

graph/flow/control_flow_lt.go

@@ -140,7 +140,9 @@ func (lt *lengauerTarjan) dfs(g graph.Directed, v graph.Node) {
 	ltv.label = ltv
 	lt.nodes = append(lt.nodes, ltv)
 
-	for _, w := range graph.NodesOf(g.From(v.ID())) {
+	to := g.From(v.ID())
+	for to.Next() {
+		w := to.Node()
 		wid := w.ID()
 
 		idx, ok := lt.indexOf[wid]

graph/flow/control_flow_slt.go

@@ -162,7 +162,9 @@ func (lt *sLengauerTarjan) dfs(g graph.Directed, v graph.Node) {
 	ltv.label = ltv
 	lt.nodes = append(lt.nodes, ltv)
 
-	for _, w := range graph.NodesOf(g.From(v.ID())) {
+	to := g.From(v.ID())
+	for to.Next() {
+		w := to.Node()
 		wid := w.ID()
 
 		idx, ok := lt.indexOf[wid]

graph/network/betweenness.go

@@ -117,7 +117,9 @@ func brandes(g graph.Graph, accumulate func(s graph.Node, stack linear.NodeStack
 			v := queue.Dequeue()
 			vid := v.ID()
 			stack.Push(v)
-			for _, w := range graph.NodesOf(g.From(vid)) {
+			to := g.From(vid)
+			for to.Next() {
+				w := to.Node()
 				wid := w.ID()
 				// w found for the first time?
 				if d[wid] < 0 {

graph/network/hits.go

@@ -33,10 +33,14 @@ func HITS(g graph.Directed, tol float64) map[int64]HubAuthority {
 	nodesLinkedFrom := make([][]int, len(nodes))
 	for i, n := range nodes {
 		id := n.ID()
-		for _, u := range graph.NodesOf(g.To(id)) {
+		from := g.To(id)
+		for from.Next() {
+			u := from.Node()
 			nodesLinkingTo[i] = append(nodesLinkingTo[i], indexOf[u.ID()])
 		}
-		for _, v := range graph.NodesOf(g.From(id)) {
+		to := g.From(id)
+		for to.Next() {
+			v := to.Node()
 			nodesLinkedFrom[i] = append(nodesLinkedFrom[i], indexOf[v.ID()])
 		}
 	}

graph/path/a_star.go

@@ -62,7 +62,9 @@ func AStar(s, t graph.Node, g traverse.Graph, h Heuristic) (path Shortest, expan
 		}
 
 		visited.Add(uid)
-		for _, v := range graph.NodesOf(g.From(u.node.ID())) {
+		to := g.From(u.node.ID())
+		for to.Next() {
+			v := to.Node()
 			vid := v.ID()
 			if visited.Has(vid) {
 				continue

graph/path/bellman_ford_moore.go

@@ -48,7 +48,9 @@ func BellmanFordFrom(u graph.Node, g graph.Graph) (path Shortest, ok bool) {
 		uid := u.ID()
 		j := path.indexOf[uid]
 
-		for _, v := range graph.NodesOf(g.From(uid)) {
+		to := g.From(uid)
+		for to.Next() {
+			v := to.Node()
 			vid := v.ID()
 			k := path.indexOf[vid]
 			w, ok := weight(uid, vid)

graph/path/dijkstra.go

@@ -58,7 +58,9 @@ func DijkstraFrom(u graph.Node, g traverse.Graph) Shortest {
 			continue
 		}
 		mnid := mid.node.ID()
-		for _, v := range graph.NodesOf(g.From(mnid)) {
+		to := g.From(mnid)
+		for to.Next() {
+			v := to.Node()
 			vid := v.ID()
 			j, ok := path.indexOf[vid]
 			if !ok {
@@ -123,7 +125,9 @@ func dijkstraAllPaths(g graph.Graph, paths AllShortest) {
 				paths.dist.Set(i, k, mid.dist)
 			}
 			mnid := mid.node.ID()
-			for _, v := range graph.NodesOf(g.From(mnid)) {
+			to := g.From(mnid)
+			for to.Next() {
+				v := to.Node()
 				vid := v.ID()
 				j := paths.indexOf[vid]
 				w, ok := weight(mnid, vid)

graph/path/dynamic/dstarlite.go

@@ -87,7 +87,9 @@ func NewDStarLite(s, t graph.Node, g graph.Graph, h path.Heuristic, m WorldModel
 
 	d.queue.insert(d.t, key{d.heuristic(s, t), 0})
 
-	for _, n := range graph.NodesOf(g.Nodes()) {
+	nodes := g.Nodes()
+	for nodes.Next() {
+		n := nodes.Node()
 		switch n.ID() {
 		case d.s.ID():
 			d.model.AddNode(d.s)
@@ -97,9 +99,13 @@ func NewDStarLite(s, t graph.Node, g graph.Graph, h path.Heuristic, m WorldModel
 			d.model.AddNode(newDStarLiteNode(n))
 		}
 	}
-	for _, u := range graph.NodesOf(d.model.Nodes()) {
+	model := d.model.Nodes()
+	for model.Next() {
+		u := model.Node()
 		uid := u.ID()
-		for _, v := range graph.NodesOf(g.From(uid)) {
+		to := g.From(uid)
+		for to.Next() {
+			v := to.Node()
 			vid := v.ID()
 			w := edgeWeight(d.weight, uid, vid)
 			if w < 0 {
@@ -195,8 +201,9 @@ func (d *DStarLite) findShortestPath() {
 		case u.g > u.rhs:
 			u.g = u.rhs
 			d.queue.remove(u)
-			for _, _s := range graph.NodesOf(d.model.To(uid)) {
+			from := d.model.To(uid)
-				s := _s.(*dStarLiteNode)
+			for from.Next() {
+				s := from.Node().(*dStarLiteNode)
 				sid := s.ID()
 				if sid != d.t.ID() {
 					s.rhs = math.Min(s.rhs, edgeWeight(d.model.Weight, sid, uid)+u.g)
@@ -212,7 +219,9 @@ func (d *DStarLite) findShortestPath() {
 				if s.rhs == edgeWeight(d.model.Weight, sid, uid)+gOld {
 					if s.ID() != d.t.ID() {
 						s.rhs = math.Inf(1)
-						for _, t := range graph.NodesOf(d.model.From(sid)) {
+						to := d.model.From(sid)
+						for to.Next() {
+							t := to.Node()
 							tid := t.ID()
 							s.rhs = math.Min(s.rhs, edgeWeight(d.model.Weight, sid, tid)+t.(*dStarLiteNode).g)
 						}
@@ -249,8 +258,9 @@ func (d *DStarLite) Step() bool {
 
 	var next *dStarLiteNode
 	dsid := d.s.ID()
-	for _, _s := range graph.NodesOf(d.model.From(dsid)) {
+	to := d.model.From(dsid)
-		s := _s.(*dStarLiteNode)
+	for to.Next() {
+		s := to.Node().(*dStarLiteNode)
 		w := edgeWeight(d.model.Weight, dsid, s.ID()) + s.g
 		if w < min || (w == min && s.rhs < rhs) {
 			next = s
@@ -319,7 +329,9 @@ func (d *DStarLite) UpdateWorld(changes []graph.Edge) {
 		} else if u.rhs == cOld+v.g {
 			if uid != d.t.ID() {
 				u.rhs = math.Inf(1)
-				for _, t := range graph.NodesOf(d.model.From(uid)) {
+				to := d.model.From(uid)
+				for to.Next() {
+					t := to.Node()
 					u.rhs = math.Min(u.rhs, edgeWeight(d.model.Weight, uid, t.ID())+t.(*dStarLiteNode).g)
 				}
 			}
@@ -364,8 +376,9 @@ func (d *DStarLite) Path() (p []graph.Node, weight float64) {
 			cost float64
 		)
 		uid := u.ID()
-		for _, _v := range graph.NodesOf(d.model.From(uid)) {
+		to := d.model.From(uid)
-			v := _v.(*dStarLiteNode)
+		for to.Next() {
+			v := to.Node().(*dStarLiteNode)
 			vid := v.ID()
 			w := edgeWeight(d.model.Weight, uid, vid)
 			if rhs := w + v.g; rhs < min || (rhs == min && v.rhs < rhsMin) {

graph/topo/johnson_cycles.go

@@ -145,7 +145,9 @@ func johnsonGraphFrom(g graph.Directed) johnsonGraph {
 	for i, u := range nodes {
 		uid := u.ID()
 		c.index[uid] = i
-		for _, v := range graph.NodesOf(g.From(uid)) {
+		to := g.From(uid)
+		for to.Next() {
+			v := to.Node()
 			if c.succ[uid] == nil {
 				c.succ[uid] = make(set.Int64s)
 				c.nodes.Add(uid)

graph/topo/paton_cycles.go

@@ -37,7 +37,9 @@ func UndirectedCyclesIn(g graph.Undirected) [][]graph.Node {
 			u := tree.Pop()
 			uid := u.ID()
 			adj := from[uid]
-			for _, v := range graph.NodesOf(g.From(uid)) {
+			it := g.From(uid)
+			for it.Next() {
+				v := it.Node()
 				vid := v.ID()
 				switch {
 				case uid == vid: