summaryrefslogtreecommitdiff
path: root/src/mongo/db/pipeline/value_comparator.h
blob: fc4baab0433676f33de5a0a4fb40255cee437d6b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
/**
 *    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