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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 comparer provides interface and implementation for ordering
// sets of data.
package comparer
// BasicComparer is the interface that wraps the basic Compare method.
type BasicComparer interface {
// Compare returns -1, 0, or +1 depending on whether a is 'less than',
// 'equal to' or 'greater than' b. The two arguments can only be 'equal'
// if their contents are exactly equal. Furthermore, the empty slice
// must be 'less than' any non-empty slice.
Compare(a, b []byte) int
}
// Comparer defines a total ordering over the space of []byte keys: a 'less
// than' relationship.
type Comparer interface {
BasicComparer
// Name returns name of the comparer.
//
// The Level-DB on-disk format stores the comparer name, and opening a
// database with a different comparer from the one it was created with
// will result in an error.
//
// An implementation to a new name whenever the comparer implementation
// changes in a way that will cause the relative ordering of any two keys
// to change.
//
// Names starting with "leveldb." are reserved and should not be used
// by any users of this package.
Name() string
// Bellow are advanced functions used used to reduce the space requirements
// for internal data structures such as index blocks.
// Separator appends a sequence of bytes x to dst such that a <= x && x < b,
// where 'less than' is consistent with Compare. An implementation should
// return nil if x equal to a.
//
// Either contents of a or b should not by any means modified. Doing so
// may cause corruption on the internal state.
Separator(dst, a, b []byte) []byte
// Successor appends a sequence of bytes x to dst such that x >= b, where
// 'less than' is consistent with Compare. An implementation should return
// nil if x equal to b.
//
// Contents of b should not by any means modified. Doing so may cause
// corruption on the internal state.
Successor(dst, b []byte) []byte
}
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