Base nexting on interface satisfaction

This is done unsubtlely at the moment and there is plenty of room for
optimisation of assertion location to prevent repeated reasserting as is
done now.

graph/iterator.go

@@ -14,8 +14,7 @@
 
 package graph
 
-// Define the general iterator interface, as well as the Base iterator which all
+// Define the general iterator interface.
-// iterators can "inherit" from to get default iterator functionality.
 
 import (
 	"strings"
@@ -86,19 +85,10 @@ type Iterator interface {
 	// All of them should set iterator.Last to be the last returned value, to
 	// make results work.
 	//
-	// Next() advances the iterator and returns the next valid result. Returns
-	// (<value>, true) or (nil, false)
-	Next() (Value, bool)
-
 	// NextResult() advances iterators that may have more than one valid result,
 	// from the bottom up.
 	NextResult() bool
 
-	// Return whether this iterator is reliably nextable. Most iterators are.
-	// However, some iterators, like "not" are, by definition, the whole database
-	// except themselves. Next() on these is unproductive, if impossible.
-	CanNext() bool
-
 	// Check(), given a value, returns whether or not that value is within the set
 	// held by this iterator.
 	Check(Value) bool
@@ -145,6 +135,25 @@ type Iterator interface {
 	UID() uint64
 }
 
+type Nexter interface {
+	// Next() advances the iterator and returns the next valid result. Returns
+	// (<value>, true) or (nil, false)
+	Next() (Value, bool)
+
+	Iterator
+}
+
+// Next is a convenience function that conditionally calls the Next method
+// of an Iterator if it is a Nexter. If the Iterator is not a Nexter, Next
+// return a nil Value and false.
+func Next(it Iterator) (Value, bool) {
+	if n, ok := it.(Nexter); ok {
+		return n.Next()
+	}
+	glog.Errorln("Nexting an un-nextable iterator")
+	return nil, false
+}
+
 // FixedIterator wraps iterators that are modifiable by addition of fixed value sets.
 type FixedIterator interface {
 	Iterator

graph/iterator/all_iterator.go

@@ -31,7 +31,6 @@ import (
 
 // An All iterator across a range of int64 values, from `max` to `min`.
 type Int64 struct {
-	Base
 	uid      uint64
 	tags     graph.Tagger
 	max, min int64

graph/iterator/and_iterator.go

@@ -22,10 +22,9 @@ import (
 	"github.com/google/cayley/graph"
 )
 
-// The And iterator. Consists of a Base and a number of subiterators, the primary of which will
+// The And iterator. Consists of a number of subiterators, the primary of which will
 // be Next()ed if next is called.
 type And struct {
-	Base
 	uid               uint64
 	tags              graph.Tagger
 	internalIterators []graph.Iterator
@@ -60,7 +59,7 @@ func (it *And) Tagger() *graph.Tagger {
 	return &it.tags
 }
 
-// Overrides Base TagResults, as it needs to add it's own results and
+// An extended TagResults, as it needs to add it's own results and
 // recurse down it's subiterators.
 func (it *And) TagResults(dst map[string]graph.Value) {
 	for _, tag := range it.tags.Tags() {
@@ -161,7 +160,7 @@ func (it *And) Next() (graph.Value, bool) {
 	var curr graph.Value
 	var exists bool
 	for {
-		curr, exists = it.primaryIt.Next()
+		curr, exists = graph.Next(it.primaryIt)
 		if !exists {
 			return graph.NextLogOut(it, nil, false)
 		}

graph/iterator/and_iterator_optimize.go

@@ -145,14 +145,14 @@ func optimizeOrder(its []graph.Iterator) []graph.Iterator {
 	// all of it's contents, and to Check() each of those against everyone
 	// else.
 	for _, it := range its {
-		if !it.CanNext() {
+		if _, canNext := it.(graph.Nexter); !canNext {
 			bad = append(bad, it)
 			continue
 		}
 		rootStats := it.Stats()
 		cost := rootStats.NextCost
 		for _, f := range its {
-			if !f.CanNext() {
+			if _, canNext := it.(graph.Nexter); !canNext {
 				continue
 			}
 			if f == it {
@@ -177,7 +177,7 @@ func optimizeOrder(its []graph.Iterator) []graph.Iterator {
 
 	// ... push everyone else after...
 	for _, it := range its {
-		if !it.CanNext() {
+		if _, canNext := it.(graph.Nexter); !canNext {
 			continue
 		}
 		if it != best {

graph/iterator/fixed_iterator.go

@@ -30,7 +30,6 @@ import (
 // A Fixed iterator consists of it's values, an index (where it is in the process of Next()ing) and
 // an equality function.
 type Fixed struct {
-	Base
 	uid       uint64
 	tags      graph.Tagger
 	values    []graph.Value

graph/iterator/hasa_iterator.go

@@ -46,7 +46,6 @@ import (
 // a primary subiterator, a direction in which the triples for that subiterator point,
 // and a temporary holder for the iterator generated on Check().
 type HasA struct {
-	Base
 	uid       uint64
 	tags      graph.Tagger
 	ts        graph.TripleStore
@@ -159,7 +158,7 @@ func (it *HasA) Check(val graph.Value) bool {
 // another match is made.
 func (it *HasA) GetCheckResult() bool {
 	for {
-		linkVal, ok := it.resultIt.Next()
+		linkVal, ok := graph.Next(it.resultIt)
 		if !ok {
 			break
 		}
@@ -198,7 +197,7 @@ func (it *HasA) Next() (graph.Value, bool) {
 	}
 	it.resultIt = &Null{}
 
-	tID, ok := it.primaryIt.Next()
+	tID, ok := graph.Next(it.primaryIt)
 	if !ok {
 		return graph.NextLogOut(it, 0, false)
 	}

graph/iterator/iterator.go

@@ -14,8 +14,7 @@
 
 package iterator
 
-// Define the general iterator interface, as well as the Base which all
+// Define the general iterator interface.
-// iterators can "inherit" from to get default iterator functionality.
 
 import (
 	"strings"
@@ -30,14 +29,6 @@ func NextUID() uint64 {
 	return atomic.AddUint64(&nextIteratorID, 1) - 1
 }
 
-// The Base iterator is the iterator other iterators inherit from to get some
-// default functionality.
-type Base struct {
-}
-
-// Accessor
-func (it *Base) CanNext() bool { return true }
-
 // Here we define the simplest iterator -- the Null iterator. It contains nothing.
 // It is the empty set. Often times, queries that contain one of these match nothing,
 // so it's important to give it a special iterator.
@@ -88,8 +79,6 @@ func (it *Null) DebugString(indent int) string {
 	return strings.Repeat(" ", indent) + "(null)"
 }
 
-func (it *Null) CanNext() bool { return true }
-
 func (it *Null) Next() (graph.Value, bool) {
 	return nil, false
 }

graph/iterator/linksto_iterator.go

@@ -40,7 +40,6 @@ import (
 // for each node) the subiterator, and the direction the iterator comes from.
 // `next_it` is the tempoarary iterator held per result in `primary_it`.
 type LinksTo struct {
-	Base
 	uid       uint64
 	tags      graph.Tagger
 	ts        graph.TripleStore
@@ -155,10 +154,10 @@ func (it *LinksTo) Optimize() (graph.Iterator, bool) {
 // Next()ing a LinksTo operates as described above.
 func (it *LinksTo) Next() (graph.Value, bool) {
 	graph.NextLogIn(it)
-	val, ok := it.nextIt.Next()
+	val, ok := graph.Next(it.nextIt)
 	if !ok {
 		// Subiterator is empty, get another one
-		candidate, ok := it.primaryIt.Next()
+		candidate, ok := graph.Next(it.primaryIt)
 		if !ok {
 			// We're out of nodes in our subiterator, so we're done as well.
 			return graph.NextLogOut(it, 0, false)

graph/iterator/optional_iterator.go

@@ -30,8 +30,6 @@ import (
 	"fmt"
 	"strings"
 
-	"github.com/barakmich/glog"
-
 	"github.com/google/cayley/graph"
 )
 
@@ -78,16 +76,6 @@ func (it *Optional) Clone() graph.Iterator {
 	return out
 }
 
-// FIXME(kortschak) When we create a Nexter interface the
-// following two methods need to go away.
-
-// Nexting the iterator is unsupported -- error and return an empty set.
-// (As above, a reasonable alternative would be to Next() an all iterator)
-func (it *Optional) Next() (graph.Value, bool) {
-	glog.Errorln("Nexting an un-nextable iterator")
-	return nil, false
-}
-
 // DEPRECATED
 func (it *Optional) ResultTree() *graph.ResultTree {
 	return graph.NewResultTree(it.Result())

graph/iterator/or_iterator.go

@@ -29,7 +29,6 @@ import (
 )
 
 type Or struct {
-	Base
 	uid               uint64
 	tags              graph.Tagger
 	isShortCircuiting bool
@@ -156,7 +155,7 @@ func (it *Or) Next() (graph.Value, bool) {
 			firstTime = true
 		}
 		curIt := it.internalIterators[it.currentIterator]
-		curr, exists = curIt.Next()
+		curr, exists = graph.Next(curIt)
 		if !exists {
 			if it.isShortCircuiting && !firstTime {
 				return graph.NextLogOut(it, nil, false)

graph/iterator/or_iterator_test.go

@@ -24,7 +24,7 @@ import (
 func iterated(it graph.Iterator) []int {
 	var res []int
 	for {
-		val, ok := it.Next()
+		val, ok := graph.Next(it)
 		if !ok {
 			break
 		}

graph/iterator/query_shape.go

@@ -129,7 +129,7 @@ func (qs *queryShape) MakeNode(it graph.Iterator) *Node {
 	case graph.Fixed:
 		n.IsFixed = true
 		for {
-			val, more := it.Next()
+			val, more := graph.Next(it)
 			if !more {
 				break
 			}

graph/iterator/value_comparison_iterator.go

@@ -46,7 +46,6 @@ const (
 )
 
 type Comparison struct {
-	Base
 	uid    uint64
 	tags   graph.Tagger
 	subIt  graph.Iterator
@@ -132,7 +131,7 @@ func (it *Comparison) Next() (graph.Value, bool) {
 	var val graph.Value
 	var ok bool
 	for {
-		val, ok = it.subIt.Next()
+		val, ok = graph.Next(it.subIt)
 		if !ok {
 			return nil, false
 		}

graph/leveldb/all_iterator.go

@@ -27,7 +27,6 @@ import (
 )
 
 type AllIterator struct {
-	iterator.Base
 	uid    uint64
 	tags   graph.Tagger
 	prefix []byte

graph/leveldb/iterator.go

@@ -27,7 +27,6 @@ import (
 )
 
 type Iterator struct {
-	iterator.Base
 	uid            uint64
 	tags           graph.Tagger
 	nextPrefix     []byte

graph/leveldb/leveldb_test.go

@@ -45,7 +45,7 @@ func makeTripleSet() []*graph.Triple {
 func iteratedTriples(ts graph.TripleStore, it graph.Iterator) []*graph.Triple {
 	var res ordered
 	for {
-		val, ok := it.Next()
+		val, ok := graph.Next(it)
 		if !ok {
 			break
 		}
@@ -85,7 +85,7 @@ func (o ordered) Swap(i, j int) { o[i], o[j] = o[j], o[i] }
 func iteratedNames(ts graph.TripleStore, it graph.Iterator) []string {
 	var res []string
 	for {
-		val, ok := it.Next()
+		val, ok := graph.Next(it)
 		if !ok {
 			break
 		}
@@ -265,7 +265,7 @@ func TestIterator(t *testing.T) {
 	it.Reset()
 
 	it = ts.TriplesAllIterator()
-	edge, _ := it.Next()
+	edge, _ := graph.Next(it)
 	triple := ts.Triple(edge)
 	set := makeTripleSet()
 	var ok bool
@@ -433,10 +433,10 @@ func TestOptimize(t *testing.T) {
 		t.Errorf("Optimized iteration does not match original")
 	}
 
-	oldIt.Next()
+	graph.Next(oldIt)
 	oldResults := make(map[string]graph.Value)
 	oldIt.TagResults(oldResults)
-	newIt.Next()
+	graph.Next(newIt)
 	newResults := make(map[string]graph.Value)
 	newIt.TagResults(newResults)
 	if !reflect.DeepEqual(newResults, oldResults) {

graph/leveldb/triplestore_iterator_optimize.go

@@ -37,7 +37,7 @@ func (ts *TripleStore) optimizeLinksTo(it *iterator.LinksTo) (graph.Iterator, bo
 	if primary.Type() == graph.Fixed {
 		size, _ := primary.Size()
 		if size == 1 {
-			val, ok := primary.Next()
+			val, ok := graph.Next(primary)
 			if !ok {
 				panic("Sizes lie")
 			}

graph/memstore/iterator.go

@@ -26,7 +26,6 @@ import (
 )
 
 type Iterator struct {
-	iterator.Base
 	uid       uint64
 	tags      graph.Tagger
 	tree      *llrb.LLRB

graph/memstore/triplestore_iterator_optimize.go

@@ -37,7 +37,7 @@ func (ts *TripleStore) optimizeLinksTo(it *iterator.LinksTo) (graph.Iterator, bo
 	if primary.Type() == graph.Fixed {
 		size, _ := primary.Size()
 		if size == 1 {
-			val, ok := primary.Next()
+			val, ok := graph.Next(primary)
 			if !ok {
 				panic("Sizes lie")
 			}

graph/memstore/triplestore_test.go

@@ -189,7 +189,7 @@ func TestRemoveTriple(t *testing.T) {
 	hasa := iterator.NewHasA(ts, innerAnd, graph.Object)
 
 	newIt, _ := hasa.Optimize()
-	_, ok := newIt.Next()
+	_, ok := graph.Next(newIt)
 	if ok {
 		t.Error("E should not have any followers.")
 	}

graph/mongo/iterator.go

@@ -27,7 +27,6 @@ import (
 )
 
 type Iterator struct {
-	iterator.Base
 	uid        uint64
 	tags       graph.Tagger
 	ts         *TripleStore

graph/mongo/triplestore_iterator_optimize.go

@@ -37,7 +37,7 @@ func (ts *TripleStore) optimizeLinksTo(it *iterator.LinksTo) (graph.Iterator, bo
 	if primary.Type() == graph.Fixed {
 		size, _ := primary.Size()
 		if size == 1 {
-			val, ok := primary.Next()
+			val, ok := graph.Next(primary)
 			if !ok {
 				panic("Sizes lie")
 			}

graph/result_tree_evaluator.go

@@ -40,7 +40,7 @@ func (t *ResultTree) AddSubtree(sub *ResultTree) {
 	t.subtrees = append(t.subtrees, sub)
 }
 
-func StringResultTreeEvaluator(it Iterator) string {
+func StringResultTreeEvaluator(it Nexter) string {
 	ok := true
 	out := ""
 	for {
@@ -59,6 +59,6 @@ func StringResultTreeEvaluator(it Iterator) string {
 	return out
 }
 
-func PrintResultTreeEvaluator(it Iterator) {
+func PrintResultTreeEvaluator(it Nexter) {
 	fmt.Print(StringResultTreeEvaluator(it))
 }

graph/sexp/parser_test.go

@@ -65,7 +65,7 @@ func TestMemstoreBackedSexp(t *testing.T) {
 		if it.Type() != test.typ {
 			t.Errorf("Incorrect type for %s, got:%q expect %q", test.message, it.Type(), test.expect)
 		}
-		got, ok := it.Next()
+		got, ok := graph.Next(it)
 		if !ok {
 			t.Errorf("Failed to %s", test.message)
 		}
@@ -86,7 +86,7 @@ func TestTreeConstraintParse(t *testing.T) {
 	if it.Type() != graph.And {
 		t.Error("Odd iterator tree. Got: %s", it.DebugString(0))
 	}
-	out, ok := it.Next()
+	out, ok := graph.Next(it)
 	if !ok {
 		t.Error("Got no results")
 	}
@@ -103,7 +103,7 @@ func TestTreeConstraintTagParse(t *testing.T) {
 		"(:like\n" +
 		"($a (:is :good))))"
 	it := BuildIteratorTreeForQuery(ts, query)
-	_, ok := it.Next()
+	_, ok := graph.Next(it)
 	if !ok {
 		t.Error("Got no results")
 	}
@@ -133,14 +133,14 @@ func TestMultipleConstraintParse(t *testing.T) {
 	if it.Type() != graph.And {
 		t.Error("Odd iterator tree. Got: %s", it.DebugString(0))
 	}
-	out, ok := it.Next()
+	out, ok := graph.Next(it)
 	if !ok {
 		t.Error("Got no results")
 	}
 	if out != ts.ValueOf("i") {
 		t.Errorf("Got %d, expected %d", out, ts.ValueOf("i"))
 	}
-	_, ok = it.Next()
+	_, ok = graph.Next(it)
 	if ok {
 		t.Error("Too many results")
 	}

graph/sexp/session.go

@@ -77,7 +77,7 @@ func (s *Session) ExecInput(input string, out chan interface{}, limit int) {
 	}
 	nResults := 0
 	for {
-		_, ok := it.Next()
+		_, ok := graph.Next(it)
 		if !ok {
 			break
 		}

query/gremlin/finals.go

@@ -151,7 +151,7 @@ func runIteratorToArray(it graph.Iterator, ses *Session, limit int) []map[string
 		if ses.doHalt {
 			return nil
 		}
-		_, ok := it.Next()
+		_, ok := graph.Next(it)
 		if !ok {
 			break
 		}
@@ -187,7 +187,7 @@ func runIteratorToArrayNoTags(it graph.Iterator, ses *Session, limit int) []stri
 		if ses.doHalt {
 			return nil
 		}
-		val, ok := it.Next()
+		val, ok := graph.Next(it)
 		if !ok {
 			break
 		}
@@ -208,7 +208,7 @@ func runIteratorWithCallback(it graph.Iterator, ses *Session, callback otto.Valu
 		if ses.doHalt {
 			return
 		}
-		_, ok := it.Next()
+		_, ok := graph.Next(it)
 		if !ok {
 			break
 		}
@@ -249,7 +249,7 @@ func runIteratorOnSession(it graph.Iterator, ses *Session) {
 		if ses.doHalt {
 			return
 		}
-		_, ok := it.Next()
+		_, ok := graph.Next(it)
 		if !ok {
 			break
 		}

query/mql/session.go

@@ -88,7 +88,7 @@ func (s *Session) ExecInput(input string, c chan interface{}, limit int) {
 		glog.V(2).Infoln(it.DebugString(0))
 	}
 	for {
-		_, ok := it.Next()
+		_, ok := graph.Next(it)
 		if !ok {
 			break
 		}