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/**
* Copyright (C) 2016 MongoDB Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License, version 3,
* as published by the Free Software Foundation.
*
* 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
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
* 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 GNU Affero General 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 <initializer_list>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include "mongo/base/disallow_copying.h"
#include "mongo/bson/bsonobj.h"
#include "mongo/util/assert_util.h"
namespace mongo {
/**
* A BSONObj::ComparatorInterface is an abstract class for comparing BSONObj objects. Usage for
* comparing two BSON objects, 'lhs' and 'rhs', where 'comparator' is an instance of a class
* implementing this interface, is as shown below:
*
* bool lessThan = comparator.evaluate(lhs < rhs);
* bool lessThanOrEqual = comparator.evaluate(lhs <= rhs);
* bool equal = comparator.evaluate(lhs == rhs);
* bool greaterThanOrEqual = comparator.evaluate(lhs >= rhs);
* bool greaterThan = comparator.evaluate(lhs > rhs);
* bool notEqual = comparator.evaluate(lhs != rhs);
*
* Can also be used to obtain function objects compatible for use with standard library algorithms
* such as std::sort, and to construct STL sets and maps which respect this comparator.
*
* All methods are thread-safe.
*/
class BSONObj::ComparatorInterface {
MONGO_DISALLOW_COPYING(ComparatorInterface);
public:
/**
* Functor compatible for use with ordered STL containers.
*/
class LessThan {
public:
explicit LessThan(const ComparatorInterface* comparator) : _comparator(comparator) {}
bool operator()(const BSONObj& lhs, const BSONObj& rhs) const {
return _comparator->compare(lhs, rhs) < 0;
}
private:
const ComparatorInterface* _comparator;
};
/**
* Functor compatible for use with unordered STL containers.
*/
class EqualTo {
public:
explicit EqualTo(const ComparatorInterface* comparator) : _comparator(comparator) {}
bool operator()(const BSONObj& lhs, const BSONObj& rhs) const {
return _comparator->compare(lhs, rhs) == 0;
}
private:
const ComparatorInterface* _comparator;
};
using BSONObjSet = std::set<BSONObj, BSONObj::ComparatorInterface::LessThan>;
// TODO SERVER-23990: Make the BSONObj hash collation-aware.
using BSONObjUnorderedSet =
std::unordered_set<BSONObj, BSONObj::Hasher, BSONObj::ComparatorInterface::EqualTo>;
template <typename T>
using BSONObjIndexedMap = std::map<BSONObj, T, BSONObj::ComparatorInterface::LessThan>;
// TODO SERVER-23990: Make the BSONObj hash collation-aware.
template <typename T>
using BSONObjIndexedUnorderedMap =
std::unordered_map<BSONObj, T, BSONObj::Hasher, BSONObj::ComparatorInterface::EqualTo>;
virtual ~ComparatorInterface() = default;
/**
* Compares two BSONObj objects. Returns <0, 0, >0 if 'lhs' < 'rhs', 'lhs' == 'rhs', or 'lhs' >
* 'rhs' respectively.
*/
virtual int compare(const BSONObj& lhs, const BSONObj& rhs) const = 0;
/**
* Evaluates a deferred comparison object generated by invocation of one of the BSONObj operator
* overloads for relops.
*/
bool evaluate(BSONObj::DeferredComparison deferredComparison) const {
int cmp = compare(deferredComparison.lhs, deferredComparison.rhs);
switch (deferredComparison.type) {
case BSONObj::DeferredComparison::Type::kLT:
return cmp < 0;
case BSONObj::DeferredComparison::Type::kLTE:
return cmp <= 0;
case BSONObj::DeferredComparison::Type::kEQ:
return cmp == 0;
case BSONObj::DeferredComparison::Type::kGT:
return cmp > 0;
case BSONObj::DeferredComparison::Type::kGTE:
return cmp >= 0;
case BSONObj::DeferredComparison::Type::kNE:
return cmp != 0;
}
MONGO_UNREACHABLE;
}
/**
* Returns a function object which computes whether one BSONObj is less than another under this
* comparator. This comparator must outlive the returned function object.
*/
LessThan makeLessThan() const {
return LessThan(this);
}
/**
* Returns a function object which computes whether one BSONObj is equal to another under this
* comparator. This comparator must outlive the returned function object.
*/
EqualTo makeEqualTo() const {
return EqualTo(this);
}
/**
* Constructs a BSONObjSet whose ordering is given by this comparator. This comparator must
* outlive the returned set.
*/
BSONObjSet makeBSONObjSet(std::initializer_list<BSONObj> init = {}) const {
return BSONObjSet(init, LessThan(this));
}
/**
* Constructs a BSONObjUnorderedSet whose equivalence classes are given by this
* comparator. This comparator must outlive the returned set.
*/
BSONObjUnorderedSet makeBSONObjUnorderedSet(std::initializer_list<BSONObj> init = {}) const {
// TODO SERVER-23990: Make the BSONObj hash collation-aware.
return BSONObjUnorderedSet(init, 0, BSONObj::Hasher(), EqualTo(this));
}
/**
* Constructs an ordered map from BSONObj to type T whose ordering is given by this comparator.
* This comparator must outlive the returned map.
*/
template <typename T>
BSONObjIndexedMap<T> makeBSONObjIndexedMap(
std::initializer_list<std::pair<const BSONObj, T>> init = {}) const {
return BSONObjIndexedMap<T>(init, LessThan(this));
}
/**
* Constructs an unordered map from BSONObj to type T whose ordering is given by this
* comparator. This comparator must outlive the returned map.
*/
template <typename T>
BSONObjIndexedUnorderedMap<T> makeBSONObjIndexedUnorderedMap(
std::initializer_list<std::pair<const BSONObj, T>> init = {}) const {
// TODO SERVER-23990: Make the BSONObj hash collation-aware.
return BSONObjIndexedUnorderedMap<T>(init, 0, BSONObj::Hasher(), EqualTo(this));
}
protected:
constexpr ComparatorInterface() = default;
};
using BSONObjSet = BSONObj::ComparatorInterface::BSONObjSet;
using BSONObjUnorderedSet = BSONObj::ComparatorInterface::BSONObjUnorderedSet;
template <typename T>
using BSONObjIndexedMap = BSONObj::ComparatorInterface::BSONObjIndexedMap<T>;
template <typename T>
using BSONObjIndexedUnorderedMap = BSONObj::ComparatorInterface::BSONObjIndexedUnorderedMap<T>;
} // namespace mongo
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