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iterator.go
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iterator.go
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// Copyright 2021 FerretDB Inc.
//
// 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 describes a generic Iterator interface and related utilities.
package iterator
import "errors"
// ErrIteratorDone is returned when the iterator is read to the end or closed.
var ErrIteratorDone = errors.New("iterator is read to the end or closed")
// Interface is an iterator interface.
type Interface[K, V any] interface {
// Next returns the next key/value pair, where the key is a slice index, map key, document number, etc,
// and the value is the slice or map value, next document, etc.
//
// Returned error could be (possibly wrapped) ErrIteratorDone or some fatal error
// like (possibly wrapped) context.Canceled.
// In any case, even if iterator was read to the end, and Next returned ErrIteratorDone,
// or Next returned fatal error,
// Close method still should be called.
//
// Next should return either key/value pair or error, not both and not neither.
// For example, single-value iterators should not return (key, value, ErrIteratorDone).
//
// Next should not be called concurrently with other Next calls,
// but it can be called concurrently with Close.
Next() (K, V, error)
// Close indicates that the iterator will no longer be used.
// After Close is called, future calls to Next must return ErrIteratorDone,
// even if previous call returned a different error.
//
// Close must be called.
// If it wasn't, the iterator might leak resources or panic later.
//
// Close must be concurrency-safe and may be called multiple times.
// All calls after the first should have no observable effect.
Close()
}