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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 "mongo/stdx/unordered_map.h"
#include "mongo/stdx/unordered_set.h"
#include "string_data.h"
namespace mongo {
/**
* A StringData::ComparatorInterface is an abstract class for comparing StringData objects.
*/
class StringData::ComparatorInterface {
ComparatorInterface(const ComparatorInterface&) = delete;
ComparatorInterface& operator=(const ComparatorInterface&) = delete;
public:
/**
* Functor for checking string equality under this comparator. Compatible for use with unordered
* STL containers.
*/
class EqualTo {
public:
explicit EqualTo(const ComparatorInterface* stringComparator)
: _stringComparator(stringComparator) {}
bool operator()(StringData lhs, StringData rhs) const {
return _stringComparator->compare(lhs, rhs) == 0;
}
private:
const ComparatorInterface* _stringComparator;
};
/**
* Functor for hashing strings under this comparator. Compatible for use with unordered STL
* containers.
*/
class Hasher {
public:
explicit Hasher(const ComparatorInterface* stringComparator)
: _stringComparator(stringComparator) {}
size_t operator()(StringData stringToHash) const {
return _stringComparator->hash(stringToHash);
}
private:
const ComparatorInterface* _stringComparator;
};
using StringDataUnorderedSet = stdx::unordered_set<StringData, Hasher, EqualTo>;
template <typename T>
using StringDataUnorderedMap = stdx::unordered_map<StringData, T, Hasher, EqualTo>;
ComparatorInterface() = default;
virtual ~ComparatorInterface() = default;
/**
* Compares two StringData objects.
*/
virtual int compare(StringData left, StringData right) const = 0;
/**
* Hash a StringData in a way that respects this comparator.
*/
size_t hash(StringData stringToHash) const {
size_t seed = 0;
hash_combine(seed, stringToHash);
return seed;
}
/**
* Hash a StringData in a way that respects this comparator, and return the result in the 'seed'
* in-out parameter.
*/
virtual void hash_combine(size_t& seed, StringData stringToHash) const = 0;
/**
* Returns a function object which can evaluate string equality according to this comparator.
* This comparator must outlive the returned function object.
*/
EqualTo makeEqualTo() const {
return EqualTo(this);
}
/**
* Returns a function object which can hash strings according to this comparator. This
* comparator must outlive the returned function object.
*/
Hasher makeHasher() const {
return Hasher(this);
}
/**
* Construct an empty unordered set of StringData whose equivalence classes are given by this
* comparator. This comparator must outlive the returned set.
*/
StringDataUnorderedSet makeStringDataUnorderedSet() const {
return StringDataUnorderedSet(0, makeHasher(), makeEqualTo());
}
/**
* Construct an empty unordered map from StringData to type T whose equivalence classes are
* given by this comparator. This comparator must outlive the returned set.
*/
template <typename T>
StringDataUnorderedMap<T> makeStringDataUnorderedMap() const {
return StringDataUnorderedMap<T>(0, makeHasher(), makeEqualTo());
}
};
using StringDataUnorderedSet = StringData::ComparatorInterface::StringDataUnorderedSet;
template <typename T>
using StringDataUnorderedMap = StringData::ComparatorInterface::StringDataUnorderedMap<T>;
} // namespace mongo
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