d6f94be514
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.
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) Check(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() (graph.Value, bool) {
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return nil, 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) NextResult() 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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