b1a70d99aa
This change allows a Nexter to be used in the same manner as a scanner
using a for graph.Next(it) {} construction.
It is important that graph.Next(it) and any associated it.Result() calls
operate on the same iterator.
113 lines
2.6 KiB
Go
113 lines
2.6 KiB
Go
// Copyright 2014 The Cayley Authors. All rights reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package iterator
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// Define the general iterator interface.
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import (
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"strings"
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"sync/atomic"
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"github.com/google/cayley/graph"
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)
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var nextIteratorID uint64
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func NextUID() uint64 {
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return atomic.AddUint64(&nextIteratorID, 1) - 1
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}
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// Here we define the simplest iterator -- the Null iterator. It contains nothing.
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// It is the empty set. Often times, queries that contain one of these match nothing,
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// so it's important to give it a special iterator.
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type Null struct {
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uid uint64
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tags graph.Tagger
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}
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// Fairly useless New function.
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func NewNull() *Null {
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return &Null{uid: NextUID()}
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}
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func (it *Null) UID() uint64 {
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return it.uid
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}
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func (it *Null) Tagger() *graph.Tagger {
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return &it.tags
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}
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// Fill the map based on the tags assigned to this iterator.
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func (it *Null) TagResults(dst map[string]graph.Value) {
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for _, tag := range it.tags.Tags() {
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dst[tag] = it.Result()
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}
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for tag, value := range it.tags.Fixed() {
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dst[tag] = value
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}
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}
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func (it *Null) Contains(graph.Value) bool {
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return false
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}
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func (it *Null) Clone() graph.Iterator { return NewNull() }
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// Name the null iterator.
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func (it *Null) Type() graph.Type { return graph.Null }
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// A good iterator will close itself when it returns true.
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// Null has nothing it needs to do.
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func (it *Null) Optimize() (graph.Iterator, bool) { return it, false }
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// Print the null iterator.
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func (it *Null) DebugString(indent int) string {
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return strings.Repeat(" ", indent) + "(null)"
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}
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func (it *Null) Next() bool {
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return false
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}
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func (it *Null) Result() graph.Value {
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return nil
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}
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func (it *Null) ResultTree() *graph.ResultTree {
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return graph.NewResultTree(it.Result())
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}
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func (it *Null) SubIterators() []graph.Iterator {
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return nil
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}
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func (it *Null) NextPath() bool {
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return false
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}
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func (it *Null) Size() (int64, bool) {
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return 0, true
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}
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func (it *Null) Reset() {}
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func (it *Null) Close() {}
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// A null iterator costs nothing. Use it!
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func (it *Null) Stats() graph.IteratorStats {
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return graph.IteratorStats{}
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}
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