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// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
// All rights reserved.
//
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Package iterator provides interface and implementation to traverse over
// contents of a database.
package iterator
import (
"errors"
"github.com/syndtr/goleveldb/leveldb/util"
)
var (
ErrIterReleased = errors.New("leveldb/iterator: iterator released")
)
// IteratorSeeker is the interface that wraps the 'seeks method'.
type IteratorSeeker interface {
// First moves the iterator to the first key/value pair. If the iterator
// only contains one key/value pair then First and Last would moves
// to the same key/value pair.
// It returns whether such pair exist.
First() bool
// Last moves the iterator to the last key/value pair. If the iterator
// only contains one key/value pair then First and Last would moves
// to the same key/value pair.
// It returns whether such pair exist.
Last() bool
// Seek moves the iterator to the first key/value pair whose key is greater
// than or equal to the given key.
// It returns whether such pair exist.
//
// It is safe to modify the contents of the argument after Seek returns.
Seek(key []byte) bool
// Next moves the iterator to the next key/value pair.
// It returns whether the iterator is exhausted.
Next() bool
// Prev moves the iterator to the previous key/value pair.
// It returns whether the iterator is exhausted.
Prev() bool
}
// CommonIterator is the interface that wraps common iterator methods.
type CommonIterator interface {
IteratorSeeker
// util.Releaser is the interface that wraps basic Release method.
// When called Release will releases any resources associated with the
// iterator.
util.Releaser
// util.ReleaseSetter is the interface that wraps the basic SetReleaser
// method.
util.ReleaseSetter
// TODO: Remove this when ready.
Valid() bool
// Error returns any accumulated error. Exhausting all the key/value pairs
// is not considered to be an error.
Error() error
}
// Iterator iterates over a DB's key/value pairs in key order.
//
// When encounter an error any 'seeks method' will return false and will
// yield no key/value pairs. The error can be queried by calling the Error
// method. Calling Release is still necessary.
//
// An iterator must be released after use, but it is not necessary to read
// an iterator until exhaustion.
// Also, an iterator is not necessarily safe for concurrent use, but it is
// safe to use multiple iterators concurrently, with each in a dedicated
// goroutine.
type Iterator interface {
CommonIterator
// Key returns the key of the current key/value pair, or nil if done.
// The caller should not modify the contents of the returned slice, and
// its contents may change on the next call to any 'seeks method'.
Key() []byte
// Value returns the value of the current key/value pair, or nil if done.
// The caller should not modify the contents of the returned slice, and
// its contents may change on the next call to any 'seeks method'.
Value() []byte
}
// ErrorCallbackSetter is the interface that wraps basic SetErrorCallback
// method.
//
// ErrorCallbackSetter implemented by indexed and merged iterator.
type ErrorCallbackSetter interface {
// SetErrorCallback allows set an error callback of the corresponding
// iterator. Use nil to clear the callback.
SetErrorCallback(f func(err error))
}
type emptyIterator struct {
util.BasicReleaser
err error
}
func (i *emptyIterator) rErr() {
if i.err == nil && i.Released() {
i.err = ErrIterReleased
}
}
func (*emptyIterator) Valid() bool { return false }
func (i *emptyIterator) First() bool { i.rErr(); return false }
func (i *emptyIterator) Last() bool { i.rErr(); return false }
func (i *emptyIterator) Seek(key []byte) bool { i.rErr(); return false }
func (i *emptyIterator) Next() bool { i.rErr(); return false }
func (i *emptyIterator) Prev() bool { i.rErr(); return false }
func (*emptyIterator) Key() []byte { return nil }
func (*emptyIterator) Value() []byte { return nil }
func (i *emptyIterator) Error() error { return i.err }
// NewEmptyIterator creates an empty iterator. The err parameter can be
// nil, but if not nil the given err will be returned by Error method.
func NewEmptyIterator(err error) Iterator {
return &emptyIterator{err: err}
}
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