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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 <map>
#include <set>
#include "mongo/base/string_data.h"
#include "mongo/db/pipeline/value.h"
#include "mongo/stdx/unordered_map.h"
#include "mongo/stdx/unordered_set.h"
namespace mongo {
class ValueComparator {
public:
/**
* Functor compatible for use with unordered STL containers.
*/
class EqualTo {
public:
explicit EqualTo(const ValueComparator* comparator) : _comparator(comparator) {}
bool operator()(const Value& lhs, const Value& rhs) const {
return _comparator->compare(lhs, rhs) == 0;
}
private:
const ValueComparator* _comparator;
};
/**
* Functor compatible for use with ordered STL containers.
*/
class LessThan {
public:
explicit LessThan(const ValueComparator* comparator) : _comparator(comparator) {}
bool operator()(const Value& lhs, const Value& rhs) const {
return _comparator->compare(lhs, rhs) < 0;
}
private:
const ValueComparator* _comparator;
};
/**
* Functor for computing the hash of a Value, compatible for use with unordered STL containers.
*/
class Hasher {
public:
explicit Hasher(const ValueComparator* comparator) : _comparator(comparator) {}
size_t operator()(const Value& val) const {
return _comparator->hash(val);
}
private:
const ValueComparator* _comparator;
};
// Global comparator for performing simple Value comparisons. Value comparisons that require
// special database logic, such as collations, must instantiate their own comparator.
static const ValueComparator kInstance;
/**
* Constructs a value comparator with simple comparison semantics.
*/
ValueComparator() = default;
/**
* Constructs a value comparator with special string comparison semantics.
*/
ValueComparator(const StringData::ComparatorInterface* stringComparator)
: _stringComparator(stringComparator) {}
/**
* Returns <0 if 'lhs' is less than 'rhs', 0 if 'lhs' is equal to 'rhs', and >0 if 'lhs' is
* greater than 'rhs'.
*/
int compare(const Value& lhs, const Value& rhs) const {
return Value::compare(lhs, rhs, _stringComparator);
}
/**
* Computes a hash of 'val' since that Values which compare equal under this comparator also
* have equal hashes.
*/
size_t hash(const Value& val) const {
size_t seed = 0xf0afbeef;
val.hash_combine(seed, _stringComparator);
return seed;
}
/**
* Evaluates a deferred comparison object that was generated by invoking one of the comparison
* operators on the Value class.
*/
bool evaluate(Value::DeferredComparison deferredComparison) const;
/**
* Returns a function object which computes whether one Value is equal to another under this
* comparator. This comparator must outlive the returned function object.
*/
EqualTo getEqualTo() const {
return EqualTo(this);
}
/**
* Returns a function object which computes whether one Value is less than another under this
* comparator. This comparator must outlive the returned function object.
*/
LessThan getLessThan() const {
return LessThan(this);
}
/**
* Returns a function object which computes the hash of a Value such that equal Values under
* this comparator have equal hashes.
*/
Hasher getHasher() const {
return Hasher(this);
}
/**
* Construct an empty ordered set of Values whose ordering and equivalence classes are given by
* this comparator. This comparator must outlive the returned set.
*/
std::set<Value, LessThan> makeOrderedValueSet() const {
return std::set<Value, LessThan>(LessThan(this));
}
/**
* Construct an empty unordered set of Values whose equivalence classes are given by this
* comparator. This comparator must outlive the returned set.
*/
stdx::unordered_set<Value, Hasher, EqualTo> makeUnorderedValueSet() const {
return stdx::unordered_set<Value, Hasher, EqualTo>(0, Hasher(this), EqualTo(this));
}
/**
* Construct an empty ordered map from Value to type T whose ordering and equivalence classes
* are given by this comparator. This comparator must outlive the returned set.
*/
template <typename T>
std::map<Value, T, LessThan> makeOrderedValueMap() const {
return std::map<Value, T, LessThan>(LessThan(this));
}
/**
* Construct an empty unordered map from Value to type T whose equivalence classes are given by
* this comparator. This comparator must outlive the returned set.
*/
template <typename T>
stdx::unordered_map<Value, T, Hasher, EqualTo> makeUnorderedValueMap() const {
return stdx::unordered_map<Value, T, Hasher, EqualTo>(0, Hasher(this), EqualTo(this));
}
private:
const StringData::ComparatorInterface* _stringComparator = nullptr;
};
//
// Type aliases for sets and maps of Value for use by clients of the Document/Value library.
//
using ValueSet = std::set<Value, ValueComparator::LessThan>;
using ValueUnorderedSet =
stdx::unordered_set<Value, ValueComparator::Hasher, ValueComparator::EqualTo>;
template <typename T>
using ValueMap = std::map<Value, T, ValueComparator::LessThan>;
template <typename T>
using ValueUnorderedMap =
stdx::unordered_map<Value, T, ValueComparator::Hasher, ValueComparator::EqualTo>;
} // namespace mongo
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