126 lines
2.7 KiB
Go
126 lines
2.7 KiB
Go
// Copyright 2014 The Cayley Authors. All rights reserved.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
package iterator
|
|
|
|
// Define the general iterator interface.
|
|
|
|
import (
|
|
"sync/atomic"
|
|
|
|
"github.com/google/cayley/graph"
|
|
)
|
|
|
|
var nextIteratorID uint64
|
|
|
|
func init() {
|
|
atomic.StoreUint64(&nextIteratorID, 1)
|
|
}
|
|
|
|
func NextUID() uint64 {
|
|
return atomic.AddUint64(&nextIteratorID, 1) - 1
|
|
}
|
|
|
|
// 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.
|
|
type Null struct {
|
|
uid uint64
|
|
tags graph.Tagger
|
|
}
|
|
|
|
// Fairly useless New function.
|
|
func NewNull() *Null {
|
|
return &Null{uid: NextUID()}
|
|
}
|
|
|
|
func (it *Null) UID() uint64 {
|
|
return it.uid
|
|
}
|
|
|
|
func (it *Null) Tagger() *graph.Tagger {
|
|
return &it.tags
|
|
}
|
|
|
|
// Fill the map based on the tags assigned to this iterator.
|
|
func (it *Null) TagResults(dst map[string]graph.Value) {
|
|
for _, tag := range it.tags.Tags() {
|
|
dst[tag] = it.Result()
|
|
}
|
|
|
|
for tag, value := range it.tags.Fixed() {
|
|
dst[tag] = value
|
|
}
|
|
}
|
|
|
|
func (it *Null) Contains(graph.Value) bool {
|
|
return false
|
|
}
|
|
|
|
func (it *Null) Clone() graph.Iterator { return NewNull() }
|
|
|
|
// Name the null iterator.
|
|
func (it *Null) Type() graph.Type { return graph.Null }
|
|
|
|
// A good iterator will close itself when it returns true.
|
|
// Null has nothing it needs to do.
|
|
func (it *Null) Optimize() (graph.Iterator, bool) { return it, false }
|
|
|
|
func (it *Null) Describe() graph.Description {
|
|
return graph.Description{
|
|
UID: it.UID(),
|
|
Type: it.Type(),
|
|
}
|
|
}
|
|
|
|
func (it *Null) Next() bool {
|
|
return false
|
|
}
|
|
|
|
func (it *Null) Err() error {
|
|
return nil
|
|
}
|
|
|
|
func (it *Null) Result() graph.Value {
|
|
return nil
|
|
}
|
|
|
|
func (it *Null) ResultTree() *graph.ResultTree {
|
|
return graph.NewResultTree(it.Result())
|
|
}
|
|
|
|
func (it *Null) SubIterators() []graph.Iterator {
|
|
return nil
|
|
}
|
|
|
|
func (it *Null) NextPath() bool {
|
|
return false
|
|
}
|
|
|
|
func (it *Null) Size() (int64, bool) {
|
|
return 0, true
|
|
}
|
|
|
|
func (it *Null) Reset() {}
|
|
|
|
func (it *Null) Close() error {
|
|
return nil
|
|
}
|
|
|
|
// A null iterator costs nothing. Use it!
|
|
func (it *Null) Stats() graph.IteratorStats {
|
|
return graph.IteratorStats{}
|
|
}
|
|
|
|
var _ graph.Nexter = &Null{}
|