Remove uses of container/list

graph/and_iterator.go

@@ -16,7 +16,6 @@
 package graph
 
 import (
-	"container/list"
 	"fmt"
 	"strings"
 )
@@ -28,7 +27,7 @@ type AndIterator struct {
 	internalIterators []Iterator
 	itCount           int
 	primaryIt         Iterator
-	checkList         *list.List
+	checkList         []Iterator
 }
 
 // Creates a new And iterator.
@@ -62,14 +61,12 @@ func (it *AndIterator) Clone() Iterator {
 	return and
 }
 
-// Returns a list.List of the subiterators, in order (primary iterator first).
-func (it *AndIterator) GetSubIterators() *list.List {
-	l := list.New()
-	l.PushBack(it.primaryIt)
-	for _, sub := range it.internalIterators {
-		l.PushBack(sub)
-	}
-	return l
+// Returns a slice of the subiterators, in order (primary iterator first).
+func (it *AndIterator) GetSubIterators() []Iterator {
+	iters := make([]Iterator, len(it.internalIterators)+1)
+	iters[0] = it.primaryIt
+	copy(iters[1:], it.internalIterators)
+	return iters
 }
 
 // Overrides BaseIterator TagResults, as it needs to add it's own results and
@@ -169,14 +166,14 @@ func (it *AndIterator) checkSubIts(val TSVal) bool {
 }
 
 func (it *AndIterator) checkCheckList(val TSVal) bool {
-	var isGood = true
-	for e := it.checkList.Front(); e != nil; e = e.Next() {
-		isGood = e.Value.(Iterator).Check(val)
-		if !isGood {
+	ok := true
+	for _, c := range it.checkList {
+		ok = c.Check(val)
+		if !ok {
 			break
 		}
 	}
-	return CheckLogOut(it, val, isGood)
+	return CheckLogOut(it, val, ok)
 }
 
 // Check a value against the entire iterator, in order.

graph/and_iterator_optimize.go

@@ -14,6 +14,10 @@
 
 package graph
 
+import (
+	"sort"
+)
+
 // Perhaps the most tricky file in this entire module. Really a method on the
 // AndIterator, but important enough to deserve its own file.
 //
@@ -31,42 +35,38 @@ package graph
 //
 // In short, tread lightly.
 
-import (
-	"container/list"
-)
-
 // Optimizes the AndIterator, by picking the most efficient way to Next() and
 // Check() its subiterators. For SQL fans, this is equivalent to JOIN.
 func (it *AndIterator) Optimize() (Iterator, bool) {
-	// First, let's get the list of iterators, in order (first one is Next()ed,
+	// First, let's get the slice of iterators, in order (first one is Next()ed,
 	// the rest are Check()ed)
-	oldItList := it.GetSubIterators()
+	old := it.GetSubIterators()
 
 	// And call Optimize() on our subtree, replacing each one in the order we
 	// found them. it_list is the newly optimized versions of these, and changed
 	// is another list, of only the ones that have returned replacements and
 	// changed.
-	itList := optimizeSubIterators(oldItList)
+	its := optimizeSubIterators(old)
 
 	// Close the replaced iterators (they ought to close themselves, but Close()
 	// is idempotent, so this just protects against any machinations).
-	closeIteratorList(oldItList, nil)
+	closeIteratorList(old, nil)
 
 	// If we can find only one subiterator which is equivalent to this whole and,
 	// we can replace the And...
-	out := it.optimizeReplacement(itList)
+	out := it.optimizeReplacement(its)
 	if out != nil {
 		// ...Move the tags to the replacement...
 		moveTagsTo(out, it)
 		// ...Close everyone except `out`, our replacement...
-		closeIteratorList(itList, out)
+		closeIteratorList(its, out)
 		// ...And return it.
 		return out, true
 	}
 
 	// And now, without changing any of the iterators, we reorder them. it_list is
 	// now a permutation of itself, but the contents are unchanged.
-	itList = optimizeOrder(itList)
+	its = optimizeOrder(its)
 
 	// Okay! At this point we have an optimized order.
 
@@ -75,8 +75,8 @@ func (it *AndIterator) Optimize() (Iterator, bool) {
 	newAnd := NewAndIterator()
 
 	// Add the subiterators in order.
-	for e := itList.Front(); e != nil; e = e.Next() {
-		newAnd.AddSubIterator(e.Value.(Iterator))
+	for _, sub := range its {
+		newAnd.AddSubIterator(sub)
 	}
 
 	// Move the tags hanging on us (like any good replacement).
@@ -93,35 +93,34 @@ func (it *AndIterator) Optimize() (Iterator, bool) {
 
 // Closes a list of iterators, except the one passed in `except`. Closes all
 // of the iterators in the list if `except` is nil.
-func closeIteratorList(l *list.List, except Iterator) {
-	for e := l.Front(); e != nil; e = e.Next() {
-		it := e.Value.(Iterator)
+func closeIteratorList(its []Iterator, except Iterator) {
+	for _, it := range its {
 		if it != except {
-			e.Value.(Iterator).Close()
+			it.Close()
 		}
 	}
 }
 
 // Find if there is a single subiterator which is a valid replacement for this
 // AndIterator.
-func (_ *AndIterator) optimizeReplacement(itList *list.List) Iterator {
+func (_ *AndIterator) optimizeReplacement(its []Iterator) Iterator {
 	// If we were created with no SubIterators, we're as good as Null.
-	if itList.Len() == 0 {
+	if len(its) == 0 {
 		return &NullIterator{}
 	}
-	if itList.Len() == 1 {
+	if len(its) == 1 {
 		// When there's only one iterator, there's only one choice.
-		return itList.Front().Value.(Iterator)
+		return its[0]
 	}
 	// If any of our subiterators, post-optimization, are also Null, then
 	// there's no point in continuing the branch, we will have no results
 	// and we are null as well.
-	if hasAnyNullIterators(itList) {
+	if hasAnyNullIterators(its) {
 		return &NullIterator{}
 	}
 
 	// If we have one useful iterator, use that.
-	it := hasOneUsefulIterator(itList)
+	it := hasOneUsefulIterator(its)
 	if it != nil {
 		return it
 	}
@@ -130,40 +129,40 @@ func (_ *AndIterator) optimizeReplacement(itList *list.List) Iterator {
 
 // optimizeOrder(l) takes a list and returns a list, containing the same contents
 // but with a new ordering, however it wishes.
-func optimizeOrder(l *list.List) *list.List {
-	out := list.New()
-	var bestIt Iterator
-	bestCost := int64(1 << 62)
-	// bad contains iterators that can't be (efficiently) nexted, such as
-	// "optional" or "not". Separate them out and tack them on at the end.
-	bad := list.New()
+func optimizeOrder(its []Iterator) []Iterator {
+	var (
+		// bad contains iterators that can't be (efficiently) nexted, such as
+		// "optional" or "not". Separate them out and tack them on at the end.
+		out, bad []Iterator
+		best     Iterator
+		bestCost = int64(1 << 62)
+	)
 
 	// Find the iterator with the projected "best" total cost.
 	// Total cost is defined as The Next()ed iterator's cost to Next() out
 	// all of it's contents, and to Check() each of those against everyone
 	// else.
-	for e := l.Front(); e != nil; e = e.Next() {
-		it := e.Value.(Iterator)
+	for _, it := range its {
 		if !it.Nextable() {
-			bad.PushBack(it)
+			bad = append(bad, it)
 			continue
 		}
-		rootStats := e.Value.(Iterator).GetStats()
-		projectedCost := rootStats.NextCost
-		for f := l.Front(); f != nil; f = f.Next() {
-			if !f.Value.(Iterator).Nextable() {
+		rootStats := it.GetStats()
+		cost := rootStats.NextCost
+		for _, f := range its {
+			if !f.Nextable() {
 				continue
 			}
-			if f == e {
+			if f == it {
 				continue
 			}
-			stats := f.Value.(Iterator).GetStats()
-			projectedCost += stats.CheckCost
+			stats := f.GetStats()
+			cost += stats.CheckCost
 		}
-		projectedCost = projectedCost * rootStats.Size
-		if projectedCost < bestCost {
-			bestIt = it
-			bestCost = projectedCost
+		cost *= rootStats.Size
+		if cost < bestCost {
+			best = it
+			bestCost = cost
 		}
 	}
 
@@ -172,63 +171,52 @@ func optimizeOrder(l *list.List) *list.List {
 	// useful (fail faster).
 
 	// Put the best iterator (the one we wish to Next()) at the front...
-	out.PushBack(bestIt)
-	// ...And push everyone else after...
-	for e := l.Front(); e != nil; e = e.Next() {
-		thisIt := e.Value.(Iterator)
-		if !thisIt.Nextable() {
+	out = append(out, best)
+
+	// ... push everyone else after...
+	for _, it := range its {
+		if !it.Nextable() {
 			continue
 		}
-		if thisIt != bestIt {
-			out.PushBack(thisIt)
+		if it != best {
+			out = append(out, it)
 		}
 	}
-	// ...And finally, the difficult children on the end.
-	out.PushBackList(bad)
-	return out
+
+	// ...and finally, the difficult children on the end.
+	return append(out, bad...)
 }
 
+type byCost []Iterator
+
+func (c byCost) Len() int           { return len(c) }
+func (c byCost) Less(i, j int) bool { return c[i].GetStats().CheckCost < c[j].GetStats().CheckCost }
+func (c byCost) Swap(i, j int)      { c[i], c[j] = c[j], c[i] }
+
 // optimizeCheck(l) creates an alternate check list, containing the same contents
 // but with a new ordering, however it wishes.
 func (it *AndIterator) optimizeCheck() {
-	subIts := it.GetSubIterators()
-	out := list.New()
-
-	// Find the iterator with the lowest Check() cost, push it to the front, repeat.
-	for subIts.Len() != 0 {
-		var best *list.Element
-		bestCost := int64(1 << 62)
-		for e := subIts.Front(); e != nil; e = e.Next() {
-			it := e.Value.(Iterator)
-			rootStats := it.GetStats()
-			projectedCost := rootStats.CheckCost
-			if projectedCost < bestCost {
-				best = e
-				bestCost = projectedCost
-			}
-		}
-		out.PushBack(best.Value)
-		subIts.Remove(best)
-	}
-
-	it.checkList = out
+	// GetSubIterators allocates, so this is currently safe.
+	// TODO(kortschak) Reuse it.checkList if possible.
+	// This involves providing GetSubIterators with a slice to fill.
+	// Generally this is a worthwhile thing to do in other places as well.
+	it.checkList = it.GetSubIterators()
+	sort.Sort(byCost(it.checkList))
 }
 
 // If we're replacing ourselves by a single iterator, we need to grab the
 // result tags from the iterators that, while still valid and would hold
 // the same values as this and, are not going to stay.
 // getSubTags() returns a map of the tags for all the subiterators.
-func (it *AndIterator) getSubTags() map[string]bool {
-	subs := it.GetSubIterators()
-	tags := make(map[string]bool)
-	for e := subs.Front(); e != nil; e = e.Next() {
-		it := e.Value.(Iterator)
-		for _, tag := range it.Tags() {
-			tags[tag] = true
+func (it *AndIterator) getSubTags() map[string]struct{} {
+	tags := make(map[string]struct{})
+	for _, sub := range it.GetSubIterators() {
+		for _, tag := range sub.Tags() {
+			tags[tag] = struct{}{}
 		}
 	}
 	for _, tag := range it.Tags() {
-		tags[tag] = true
+		tags[tag] = struct{}{}
 	}
 	return tags
 }
@@ -236,13 +224,13 @@ func (it *AndIterator) getSubTags() map[string]bool {
 // moveTagsTo() gets the tags for all of the src's subiterators and the
 // src itself, and moves them to dst.
 func moveTagsTo(dst Iterator, src *AndIterator) {
-	tagmap := src.getSubTags()
+	tags := src.getSubTags()
 	for _, tag := range dst.Tags() {
-		if tagmap[tag] {
-			delete(tagmap, tag)
+		if _, ok := tags[tag]; ok {
+			delete(tags, tag)
 		}
 	}
-	for k, _ := range tagmap {
+	for k := range tags {
 		dst.AddTag(k)
 	}
 }
@@ -251,24 +239,22 @@ func moveTagsTo(dst Iterator, src *AndIterator) {
 // of them. It returns two lists -- the first contains the same list as l, where
 // any replacements are made by Optimize() and the second contains the originals
 // which were replaced.
-func optimizeSubIterators(l *list.List) *list.List {
-	itList := list.New()
-	for e := l.Front(); e != nil; e = e.Next() {
-		it := e.Value.(Iterator)
-		newIt, change := it.Optimize()
-		if change {
-			itList.PushBack(newIt)
+func optimizeSubIterators(its []Iterator) []Iterator {
+	var optIts []Iterator
+	for _, it := range its {
+		o, changed := it.Optimize()
+		if changed {
+			optIts = append(optIts, o)
 		} else {
-			itList.PushBack(it.Clone())
+			optIts = append(optIts, it.Clone())
 		}
 	}
-	return itList
+	return optIts
 }
 
 // Check a list of iterators for any Null iterators.
-func hasAnyNullIterators(l *list.List) bool {
-	for e := l.Front(); e != nil; e = e.Next() {
-		it := e.Value.(Iterator)
+func hasAnyNullIterators(its []Iterator) bool {
+	for _, it := range its {
 		if it.Type() == "null" {
 			return true
 		}
@@ -280,11 +266,10 @@ func hasAnyNullIterators(l *list.List) bool {
 // nothing, and "all" which returns everything. Particularly, we want
 // to see if we're intersecting with a bunch of "all" iterators, and,
 // if we are, then we have only one useful iterator.
-func hasOneUsefulIterator(l *list.List) Iterator {
+func hasOneUsefulIterator(its []Iterator) Iterator {
 	usefulCount := 0
 	var usefulIt Iterator
-	for e := l.Front(); e != nil; e = e.Next() {
-		it := e.Value.(Iterator)
+	for _, it := range its {
 		switch it.Type() {
 		case "null", "all":
 			continue

graph/and_iterator_optimize_test.go

@@ -79,9 +79,8 @@ func TestReorderWithTag(t *testing.T) {
 	}
 	expectedTags := []string{"good", "slow"}
 	tagsOut := make([]string, 0)
-	l := newIt.GetSubIterators()
-	for e := l.Front(); e != nil; e = e.Next() {
-		for _, x := range e.Value.(Iterator).Tags() {
+	for _, sub := range newIt.GetSubIterators() {
+		for _, x := range sub.Tags() {
 			tagsOut = append(tagsOut, x)
 		}
 	}

graph/hasa_iterator.go

@@ -34,7 +34,6 @@ package graph
 // Alternatively, can be seen as the dual of the LinksTo iterator.
 
 import (
-	"container/list"
 	"fmt"
 	"strings"
 
@@ -63,11 +62,9 @@ func NewHasaIterator(ts TripleStore, subIt Iterator, dir string) *HasaIterator {
 	return &hasa
 }
 
-// Return our sole subiterator, in a list.List.
-func (it *HasaIterator) GetSubIterators() *list.List {
-	l := list.New()
-	l.PushBack(it.primaryIt)
-	return l
+// Return our sole subiterator.
+func (it *HasaIterator) GetSubIterators() []Iterator {
+	return []Iterator{it.primaryIt}
 }
 
 func (it *HasaIterator) Reset() {

graph/iterator.go

@@ -18,7 +18,6 @@ package graph
 // iterators can "inherit" from to get default iterator functionality.
 
 import (
-	"container/list"
 	"fmt"
 	"strings"
 
@@ -90,8 +89,9 @@ type Iterator interface {
 	// around internally. if it chooses to replace it with a better iterator,
 	// returns (the new iterator, true), if not, it returns (self, false).
 	Optimize() (Iterator, bool)
-	// Return a list of the subiterators for this iterator.
-	GetSubIterators() *list.List
+
+	// Return a slice of the subiterators for this iterator.
+	GetSubIterators() []Iterator
 
 	// Return a string representation of the iterator, indented by the given amount.
 	DebugString(int) string
@@ -170,18 +170,18 @@ func (it *BaseIterator) CopyTagsFrom(other_it Iterator) {
 }
 
 // Prints a silly debug string. Most classes override.
-func (n *BaseIterator) DebugString(indent int) string {
+func (it *BaseIterator) DebugString(indent int) string {
 	return fmt.Sprintf("%s(base)", strings.Repeat(" ", indent))
 }
 
 // Nothing in a base iterator.
-func (n *BaseIterator) Check(v TSVal) bool {
+func (it *BaseIterator) Check(v TSVal) bool {
 	return false
 }
 
 // Base iterators should never appear in a tree if they are, select against
 // them.
-func (n *BaseIterator) GetStats() *IteratorStats {
+func (it *BaseIterator) GetStats() *IteratorStats {
 	return &IteratorStats{100000, 100000, 100000}
 }
 
@@ -211,7 +211,7 @@ func (it *BaseIterator) Size() (int64, bool) {
 }
 
 // No subiterators. Only those with subiterators need to do anything here.
-func (it *BaseIterator) GetSubIterators() *list.List {
+func (it *BaseIterator) GetSubIterators() []Iterator {
 	return nil
 }
 
@@ -231,7 +231,8 @@ func (it *BaseIterator) TagResults(out_map *map[string]TSVal) {
 }
 
 // Nothing to clean up.
-//func (a *BaseIterator) Close() {}
+// func (it *BaseIterator) Close() {}
+
 func (it *NullIterator) Close() {}
 
 func (it *BaseIterator) Reset() {}

graph/leveldb/triplestore_iterator_optimize.go

@@ -28,21 +28,21 @@ func (ts *TripleStore) OptimizeIterator(it graph.Iterator) (graph.Iterator, bool
 }
 
 func (ts *TripleStore) optimizeLinksTo(it *graph.LinksToIterator) (graph.Iterator, bool) {
-	l := it.GetSubIterators()
-	if l.Len() != 1 {
+	subs := it.GetSubIterators()
+	if len(subs) != 1 {
 		return it, false
 	}
-	primaryIt := l.Front().Value.(graph.Iterator)
-	if primaryIt.Type() == "fixed" {
-		size, _ := primaryIt.Size()
+	primary := subs[0]
+	if primary.Type() == "fixed" {
+		size, _ := primary.Size()
 		if size == 1 {
-			val, ok := primaryIt.Next()
+			val, ok := primary.Next()
 			if !ok {
 				panic("Sizes lie")
 			}
 			newIt := ts.GetTripleIterator(it.Direction(), val)
 			newIt.CopyTagsFrom(it)
-			for _, tag := range primaryIt.Tags() {
+			for _, tag := range primary.Tags() {
 				newIt.AddFixedTag(tag, val)
 			}
 			it.Close()

graph/linksto_iterator.go

@@ -30,7 +30,6 @@ package graph
 // Can be seen as the dual of the HasA iterator.
 
 import (
-	"container/list"
 	"fmt"
 	"strings"
 )
@@ -58,120 +57,118 @@ func NewLinksToIterator(ts TripleStore, it Iterator, dir string) *LinksToIterato
 	return &lto
 }
 
-func (l *LinksToIterator) Reset() {
-	l.primaryIt.Reset()
-	if l.nextIt != nil {
-		l.nextIt.Close()
+func (it *LinksToIterator) Reset() {
+	it.primaryIt.Reset()
+	if it.nextIt != nil {
+		it.nextIt.Close()
 	}
-	l.nextIt = &NullIterator{}
+	it.nextIt = &NullIterator{}
 }
 
-func (l *LinksToIterator) Clone() Iterator {
-	out := NewLinksToIterator(l.ts, l.primaryIt.Clone(), l.direction)
-	out.CopyTagsFrom(l)
+func (it *LinksToIterator) Clone() Iterator {
+	out := NewLinksToIterator(it.ts, it.primaryIt.Clone(), it.direction)
+	out.CopyTagsFrom(it)
 	return out
 }
 
 // Return the direction under consideration.
-func (l *LinksToIterator) Direction() string { return l.direction }
+func (it *LinksToIterator) Direction() string { return it.direction }
 
 // Tag these results, and our subiterator's results.
-func (l *LinksToIterator) TagResults(out *map[string]TSVal) {
-	l.BaseIterator.TagResults(out)
-	l.primaryIt.TagResults(out)
+func (it *LinksToIterator) TagResults(out *map[string]TSVal) {
+	it.BaseIterator.TagResults(out)
+	it.primaryIt.TagResults(out)
 }
 
 // DEPRECATED
-func (l *LinksToIterator) GetResultTree() *ResultTree {
-	tree := NewResultTree(l.LastResult())
-	tree.AddSubtree(l.primaryIt.GetResultTree())
+func (it *LinksToIterator) GetResultTree() *ResultTree {
+	tree := NewResultTree(it.LastResult())
+	tree.AddSubtree(it.primaryIt.GetResultTree())
 	return tree
 }
 
 // Print the iterator.
-func (l *LinksToIterator) DebugString(indent int) string {
+func (it *LinksToIterator) DebugString(indent int) string {
 	return fmt.Sprintf("%s(%s %d direction:%s\n%s)",
 		strings.Repeat(" ", indent),
-		l.Type(), l.GetUid(), l.direction, l.primaryIt.DebugString(indent+4))
+		it.Type(), it.GetUid(), it.direction, it.primaryIt.DebugString(indent+4))
 }
 
 // If it checks in the right direction for the subiterator, it is a valid link
 // for the LinksTo.
-func (l *LinksToIterator) Check(val TSVal) bool {
-	CheckLogIn(l, val)
-	node := l.ts.GetTripleDirection(val, l.direction)
-	if l.primaryIt.Check(node) {
-		l.Last = val
-		return CheckLogOut(l, val, true)
+func (it *LinksToIterator) Check(val TSVal) bool {
+	CheckLogIn(it, val)
+	node := it.ts.GetTripleDirection(val, it.direction)
+	if it.primaryIt.Check(node) {
+		it.Last = val
+		return CheckLogOut(it, val, true)
 	}
-	return CheckLogOut(l, val, false)
+	return CheckLogOut(it, val, false)
 }
 
 // Return a list containing only our subiterator.
-func (lto *LinksToIterator) GetSubIterators() *list.List {
-	l := list.New()
-	l.PushBack(lto.primaryIt)
-	return l
+func (it *LinksToIterator) GetSubIterators() []Iterator {
+	return []Iterator{it.primaryIt}
 }
 
 // Optimize the LinksTo, by replacing it if it can be.
-func (lto *LinksToIterator) Optimize() (Iterator, bool) {
-	newPrimary, changed := lto.primaryIt.Optimize()
+func (it *LinksToIterator) Optimize() (Iterator, bool) {
+	newPrimary, changed := it.primaryIt.Optimize()
 	if changed {
-		lto.primaryIt = newPrimary
-		if lto.primaryIt.Type() == "null" {
-			lto.nextIt.Close()
-			return lto.primaryIt, true
+		it.primaryIt = newPrimary
+		if it.primaryIt.Type() == "null" {
+			it.nextIt.Close()
+			return it.primaryIt, true
 		}
 	}
 	// Ask the TripleStore if we can be replaced. Often times, this is a great
 	// optimization opportunity (there's a fixed iterator underneath us, for
 	// example).
-	newReplacement, hasOne := lto.ts.OptimizeIterator(lto)
+	newReplacement, hasOne := it.ts.OptimizeIterator(it)
 	if hasOne {
-		lto.Close()
+		it.Close()
 		return newReplacement, true
 	}
-	return lto, false
+	return it, false
 }
 
 // Next()ing a LinksTo operates as described above.
-func (l *LinksToIterator) Next() (TSVal, bool) {
-	NextLogIn(l)
-	val, ok := l.nextIt.Next()
+func (it *LinksToIterator) Next() (TSVal, bool) {
+	NextLogIn(it)
+	val, ok := it.nextIt.Next()
 	if !ok {
 		// Subiterator is empty, get another one
-		candidate, ok := l.primaryIt.Next()
+		candidate, ok := it.primaryIt.Next()
 		if !ok {
 			// We're out of nodes in our subiterator, so we're done as well.
-			return NextLogOut(l, 0, false)
+			return NextLogOut(it, 0, false)
 		}
-		l.nextIt.Close()
-		l.nextIt = l.ts.GetTripleIterator(l.direction, candidate)
+		it.nextIt.Close()
+		it.nextIt = it.ts.GetTripleIterator(it.direction, candidate)
 		// Recurse -- return the first in the next set.
-		return l.Next()
+		return it.Next()
 	}
-	l.Last = val
-	return NextLogOut(l, val, ok)
+	it.Last = val
+	return NextLogOut(it, val, ok)
 }
 
 // Close our subiterators.
-func (l *LinksToIterator) Close() {
-	l.nextIt.Close()
-	l.primaryIt.Close()
+func (it *LinksToIterator) Close() {
+	it.nextIt.Close()
+	it.primaryIt.Close()
 }
 
 // We won't ever have a new result, but our subiterators might.
-func (l *LinksToIterator) NextResult() bool {
-	return l.primaryIt.NextResult()
+func (it *LinksToIterator) NextResult() bool {
+	return it.primaryIt.NextResult()
 }
 
 // Register the LinksTo.
-func (l *LinksToIterator) Type() string { return "linksto" }
+func (it *LinksToIterator) Type() string { return "linksto" }
 
 // Return a guess as to how big or costly it is to next the iterator.
-func (l *LinksToIterator) GetStats() *IteratorStats {
-	subitStats := l.primaryIt.GetStats()
+func (it *LinksToIterator) GetStats() *IteratorStats {
+	subitStats := it.primaryIt.GetStats()
 	// TODO(barakmich): These should really come from the triplestore itself
 	fanoutFactor := int64(20)
 	checkConstant := int64(1)

graph/memstore/triplestore_iterator_optimize.go

@@ -28,21 +28,21 @@ func (ts *TripleStore) OptimizeIterator(it graph.Iterator) (graph.Iterator, bool
 }
 
 func (ts *TripleStore) optimizeLinksTo(it *graph.LinksToIterator) (graph.Iterator, bool) {
-	l := it.GetSubIterators()
-	if l.Len() != 1 {
+	subs := it.GetSubIterators()
+	if len(subs) != 1 {
 		return it, false
 	}
-	primaryIt := l.Front().Value.(graph.Iterator)
-	if primaryIt.Type() == "fixed" {
-		size, _ := primaryIt.Size()
+	primary := subs[0]
+	if primary.Type() == "fixed" {
+		size, _ := primary.Size()
 		if size == 1 {
-			val, ok := primaryIt.Next()
+			val, ok := primary.Next()
 			if !ok {
 				panic("Sizes lie")
 			}
 			newIt := ts.GetTripleIterator(it.Direction(), val)
 			newIt.CopyTagsFrom(it)
-			for _, tag := range primaryIt.Tags() {
+			for _, tag := range primary.Tags() {
 				newIt.AddFixedTag(tag, val)
 			}
 			return newIt, true

graph/mongo/triplestore_iterator_optimize.go

@@ -28,21 +28,21 @@ func (ts *TripleStore) OptimizeIterator(it graph.Iterator) (graph.Iterator, bool
 }
 
 func (ts *TripleStore) optimizeLinksTo(it *graph.LinksToIterator) (graph.Iterator, bool) {
-	l := it.GetSubIterators()
-	if l.Len() != 1 {
+	subs := it.GetSubIterators()
+	if len(subs) != 1 {
 		return it, false
 	}
-	primaryIt := l.Front().Value.(graph.Iterator)
-	if primaryIt.Type() == "fixed" {
-		size, _ := primaryIt.Size()
+	primary := subs[0]
+	if primary.Type() == "fixed" {
+		size, _ := primary.Size()
 		if size == 1 {
-			val, ok := primaryIt.Next()
+			val, ok := primary.Next()
 			if !ok {
 				panic("Sizes lie")
 			}
 			newIt := ts.GetTripleIterator(it.Direction(), val)
 			newIt.CopyTagsFrom(it)
-			for _, tag := range primaryIt.Tags() {
+			for _, tag := range primary.Tags() {
 				newIt.AddFixedTag(tag, val)
 			}
 			it.Close()

graph/or_iterator.go

@@ -22,7 +22,6 @@ package graph
 // May return the same value twice -- once for each branch.
 
 import (
-	"container/list"
 	"fmt"
 	"strings"
 )
@@ -75,13 +74,9 @@ func (it *OrIterator) Clone() Iterator {
 	return or
 }
 
-// Returns a list.List of the subiterators, in order.
-func (it *OrIterator) GetSubIterators() *list.List {
-	l := list.New()
-	for _, sub := range it.internalIterators {
-		l.PushBack(sub)
-	}
-	return l
+// Returns a list.List of the subiterators, in order. The returned slice must not be modified.
+func (it *OrIterator) GetSubIterators() []Iterator {
+	return it.internalIterators
 }
 
 // Overrides BaseIterator TagResults, as it needs to add it's own results and
@@ -236,17 +231,17 @@ func (it *OrIterator) Close() {
 }
 
 func (it *OrIterator) Optimize() (Iterator, bool) {
-	oldItList := it.GetSubIterators()
-	itList := optimizeSubIterators(oldItList)
+	old := it.GetSubIterators()
+	optIts := optimizeSubIterators(old)
 	// Close the replaced iterators (they ought to close themselves, but Close()
 	// is idempotent, so this just protects against any machinations).
-	closeIteratorList(oldItList, nil)
+	closeIteratorList(old, nil)
 	newOr := NewOrIterator()
 	newOr.isShortCircuiting = it.isShortCircuiting
 
 	// Add the subiterators in order.
-	for e := itList.Front(); e != nil; e = e.Next() {
-		newOr.AddSubIterator(e.Value.(Iterator))
+	for _, o := range optIts {
+		newOr.AddSubIterator(o)
 	}
 
 	// Move the tags hanging on us (like any good replacement).

graph/query_shape.go

@@ -105,12 +105,7 @@ func (qs *queryShape) StealNode(left *Node, right *Node) {
 }
 
 func (qs *queryShape) MakeNode(it Iterator) *Node {
-	var n Node
-	n.IsLinkNode = false
-	n.IsFixed = false
-	n.Id = qs.nodeId
-	n.Tags = make([]string, 0)
-	n.Values = make([]string, 0)
+	n := Node{Id: qs.nodeId}
 	for _, tag := range it.Tags() {
 		n.Tags = append(n.Tags, tag)
 	}
@@ -120,12 +115,10 @@ func (qs *queryShape) MakeNode(it Iterator) *Node {
 
 	switch it.Type() {
 	case "and":
-		list := it.GetSubIterators()
-		for e := list.Front(); e != nil; e = e.Next() {
-			subit := e.Value.(Iterator)
+		for _, sub := range it.GetSubIterators() {
 			qs.nodeId++
-			newNode := qs.MakeNode(subit)
-			if subit.Type() != "or" {
+			newNode := qs.MakeNode(sub)
+			if sub.Type() != "or" {
 				qs.StealNode(&n, newNode)
 			} else {
 				qs.AddNode(newNode)
@@ -149,12 +142,10 @@ func (qs *queryShape) MakeNode(it Iterator) *Node {
 		qs.AddNode(newNode)
 		qs.RemoveHasa()
 	case "or":
-		list := it.GetSubIterators()
-		for e := list.Front(); e != nil; e = e.Next() {
-			subit := e.Value.(Iterator)
+		for _, sub := range it.GetSubIterators() {
 			qs.nodeId++
-			newNode := qs.MakeNode(subit)
-			if subit.Type() == "or" {
+			newNode := qs.MakeNode(sub)
+			if sub.Type() == "or" {
 				qs.StealNode(&n, newNode)
 			} else {
 				qs.AddNode(newNode)