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fixed_iterator.go
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fixed_iterator.go
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// 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
// Defines one of the base iterators, the Fixed iterator. A fixed iterator is quite simple; it
// contains an explicit fixed array of values.
//
// A fixed iterator requires an Equality function to be passed to it, by reason that graph.Value, the
// opaque Triple store value, may not answer to ==.
import (
"fmt"
"strings"
"github.com/google/cayley/graph"
)
// 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 {
uid uint64
tags graph.Tagger
values []graph.Value
lastIndex int
cmp Equality
result graph.Value
}
// Define the signature of an equality function.
type Equality func(a, b graph.Value) bool
// Define an equality function of purely ==, which works for native types.
func BasicEquality(a, b graph.Value) bool {
if a == b {
return true
}
return false
}
// Creates a new Fixed iterator based around == equality.
func newFixed() *Fixed {
return NewFixedIteratorWithCompare(BasicEquality)
}
// Creates a new Fixed iterator with a custom comparitor.
func NewFixedIteratorWithCompare(compareFn Equality) *Fixed {
return &Fixed{
uid: NextUID(),
values: make([]graph.Value, 0, 20),
cmp: compareFn,
}
}
func (it *Fixed) UID() uint64 {
return it.uid
}
func (it *Fixed) Reset() {
it.lastIndex = 0
}
func (it *Fixed) Close() {}
func (it *Fixed) Tagger() *graph.Tagger {
return &it.tags
}
func (it *Fixed) 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 *Fixed) Clone() graph.Iterator {
out := NewFixedIteratorWithCompare(it.cmp)
for _, val := range it.values {
out.Add(val)
}
out.tags.CopyFrom(it)
return out
}
// Add a value to the iterator. The array now contains this value.
// TODO(barakmich): This ought to be a set someday, disallowing repeated values.
func (it *Fixed) Add(v graph.Value) {
it.values = append(it.values, v)
}
// Print some information about the iterator.
func (it *Fixed) DebugString(indent int) string {
value := ""
if len(it.values) > 0 {
value = fmt.Sprint(it.values[0])
}
return fmt.Sprintf("%s(%s tags: %s Size: %d id0: %d)",
strings.Repeat(" ", indent),
it.Type(),
it.tags.Fixed(),
len(it.values),
value,
)
}
// Register this iterator as a Fixed iterator.
func (it *Fixed) Type() graph.Type { return graph.Fixed }
// Check if the passed value is equal to one of the values stored in the iterator.
func (it *Fixed) Contains(v graph.Value) bool {
// Could be optimized by keeping it sorted or using a better datastructure.
// However, for fixed iterators, which are by definition kind of tiny, this
// isn't a big issue.
graph.ContainsLogIn(it, v)
for _, x := range it.values {
if it.cmp(x, v) {
it.result = x
return graph.ContainsLogOut(it, v, true)
}
}
return graph.ContainsLogOut(it, v, false)
}
// Return the next stored value from the iterator.
func (it *Fixed) Next() (graph.Value, bool) {
graph.NextLogIn(it)
if it.lastIndex == len(it.values) {
return graph.NextLogOut(it, nil, false)
}
out := it.values[it.lastIndex]
it.result = out
it.lastIndex++
return graph.NextLogOut(it, out, true)
}
// DEPRECATED
func (it *Fixed) ResultTree() *graph.ResultTree {
return graph.NewResultTree(it.Result())
}
func (it *Fixed) Result() graph.Value {
return it.result
}
func (it *Fixed) NextResult() bool {
return false
}
// No sub-iterators.
func (it *Fixed) SubIterators() []graph.Iterator {
return nil
}
// Optimize() for a Fixed iterator is simple. Returns a Null iterator if it's empty
// (so that other iterators upstream can treat this as null) or there is no
// optimization.
func (it *Fixed) Optimize() (graph.Iterator, bool) {
if len(it.values) == 1 && it.values[0] == nil {
return &Null{}, true
}
return it, false
}
// Size is the number of values stored.
func (it *Fixed) Size() (int64, bool) {
return int64(len(it.values)), true
}
// As we right now have to scan the entire list, Next and Contains are linear with the
// size. However, a better data structure could remove these limits.
func (it *Fixed) Stats() graph.IteratorStats {
return graph.IteratorStats{
ContainsCost: int64(len(it.values)),
NextCost: int64(len(it.values)),
Size: int64(len(it.values)),
}
}