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/**
* Copyright (C) 2018-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <memory>
#include <string>
#include "mongo/base/disallow_copying.h"
#include "mongo/base/string_data.h"
#include "mongo/base/string_data_comparator_interface.h"
#include "mongo/bson/bsonobj_comparator_interface.h"
#include "mongo/db/query/collation/collation_spec.h"
namespace mongo {
/**
* An interface for ordering and matching according to a collation. Instances should be retrieved
* from the CollatorFactoryInterface and may not be copied.
*
* All methods are thread-safe.
*
* Does not throw exceptions.
*/
class CollatorInterface : public StringData::ComparatorInterface {
MONGO_DISALLOW_COPYING(CollatorInterface);
public:
/**
* Every string has a corresponding ComparisonKey with respect to this collator. Two
* ComparisonKeys can be lexicographically ordered in order to obtain the collation's sort order
* and equivalence classes.
*
* A ComparisonKey is logically an owned array of bytes. It is cheap to move but potentially
* expensive to copy.
*
* ComparisonKeys may only be obtained via CollatorInterface::getComparisonKey().
*
* In general, two strings should be compared with respect to a collation using
* CollatorInterface::compare(). ComparisonKey::compare() may be faster if repeatedly comparing
* the same string(s).
*/
class ComparisonKey {
public:
/**
* Returns the underlying byte array represented by this ComparisonKey.
*
* The returned StringData may not outlive the ComparisonKey used to create it, since the
* ComparisonKey owns the underlying byte array.
*/
StringData getKeyData() const {
return StringData(_key);
}
private:
friend class CollatorInterface;
ComparisonKey(std::string key) : _key(std::move(key)) {}
std::string _key;
};
/**
* Constructs a CollatorInterface capable of computing the collation described by 'spec'.
*/
CollatorInterface(CollationSpec spec) : _spec(std::move(spec)) {}
virtual ~CollatorInterface() {}
virtual std::unique_ptr<CollatorInterface> clone() const = 0;
/**
* Returns a number < 0 if 'left' is less than 'right' with respect to the collation, a number >
* 0 if 'left' is greater than 'right' w.r.t. the collation, and 0 if 'left' and 'right' are
* equal w.r.t. the collation.
*/
virtual int compare(StringData left, StringData right) const = 0;
/**
* Hashes the string such that strings which are equal under this collation also have equal
* hashes.
*/
void hash_combine(size_t& seed, StringData stringToHash) const final;
/**
* Returns the comparison key for 'stringData', according to this collation. See ComparisonKey's
* comments for details.
*/
virtual ComparisonKey getComparisonKey(StringData stringData) const = 0;
/**
* Returns whether this collation has the same matching and sorting semantics as 'other'.
*/
bool operator==(const CollatorInterface& other) const {
return getSpec() == other.getSpec();
}
/**
* Returns whether this collation *does not* have the same matching and sorting semantics as
* 'other'.
*/
bool operator!=(const CollatorInterface& other) const {
return !(*this == other);
}
/**
* Returns a reference to the CollationSpec.
*/
const CollationSpec& getSpec() const {
return _spec;
}
/**
* Returns true if lhs and rhs are both nullptr, or if they point to equivalent collators.
*/
static bool collatorsMatch(const CollatorInterface* lhs, const CollatorInterface* rhs) {
if (lhs == nullptr && rhs == nullptr) {
return true;
}
if (lhs == nullptr || rhs == nullptr) {
return false;
}
return (*lhs == *rhs);
}
/**
* Returns a clone of 'collator'. If 'collator' is nullptr, returns the null collator.
*/
static std::unique_ptr<CollatorInterface> cloneCollator(const CollatorInterface* collator) {
if (!collator) {
return {nullptr};
}
return collator->clone();
}
protected:
static ComparisonKey makeComparisonKey(std::string key) {
return ComparisonKey(std::move(key));
}
private:
const CollationSpec _spec;
};
} // namespace mongo
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