1 
2 /**
3  *    Copyright (C) 2018-present MongoDB, Inc.
4  *
5  *    This program is free software: you can redistribute it and/or modify
6  *    it under the terms of the Server Side Public License, version 1,
7  *    as published by MongoDB, Inc.
8  *
9  *    This program is distributed in the hope that it will be useful,
10  *    but WITHOUT ANY WARRANTY; without even the implied warranty of
11  *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  *    Server Side Public License for more details.
13  *
14  *    You should have received a copy of the Server Side Public License
15  *    along with this program. If not, see
16  *    <http://www.mongodb.com/licensing/server-side-public-license>.
17  *
18  *    As a special exception, the copyright holders give permission to link the
19  *    code of portions of this program with the OpenSSL library under certain
20  *    conditions as described in each individual source file and distribute
21  *    linked combinations including the program with the OpenSSL library. You
22  *    must comply with the Server Side Public License in all respects for
23  *    all of the code used other than as permitted herein. If you modify file(s)
24  *    with this exception, you may extend this exception to your version of the
25  *    file(s), but you are not obligated to do so. If you do not wish to do so,
26  *    delete this exception statement from your version. If you delete this
27  *    exception statement from all source files in the program, then also delete
28  *    it in the license file.
29  */
30 
31 #pragma once
32 
33 #include "mongo/base/disallow_copying.h"
34 #include "mongo/stdx/unordered_map.h"
35 #include "mongo/stdx/unordered_set.h"
36 #include "string_data.h"
37 
38 namespace mongo {
39 
40 /**
41  * A StringData::ComparatorInterface is an abstract class for comparing StringData objects.
42  */
43 class StringData::ComparatorInterface {
44     MONGO_DISALLOW_COPYING(ComparatorInterface);
45 
46 public:
47     /**
48      * Functor for checking string equality under this comparator. Compatible for use with unordered
49      * STL containers.
50      */
51     class EqualTo {
52     public:
EqualTo(const ComparatorInterface * stringComparator)53         explicit EqualTo(const ComparatorInterface* stringComparator)
54             : _stringComparator(stringComparator) {}
55 
operator()56         bool operator()(StringData lhs, StringData rhs) const {
57             return _stringComparator->compare(lhs, rhs) == 0;
58         }
59 
60     private:
61         const ComparatorInterface* _stringComparator;
62     };
63 
64     /**
65      * Functor for hashing strings under this comparator. Compatible for use with unordered STL
66      * containers.
67      */
68     class Hasher {
69     public:
Hasher(const ComparatorInterface * stringComparator)70         explicit Hasher(const ComparatorInterface* stringComparator)
71             : _stringComparator(stringComparator) {}
72 
operator()73         size_t operator()(StringData stringToHash) const {
74             return _stringComparator->hash(stringToHash);
75         }
76 
77     private:
78         const ComparatorInterface* _stringComparator;
79     };
80 
81     using StringDataUnorderedSet = stdx::unordered_set<StringData, Hasher, EqualTo>;
82 
83     template <typename T>
84     using StringDataUnorderedMap = stdx::unordered_map<StringData, T, Hasher, EqualTo>;
85 
86     ComparatorInterface() = default;
87 
88     virtual ~ComparatorInterface() = default;
89 
90     /**
91      * Compares two StringData objects.
92      */
93     virtual int compare(StringData left, StringData right) const = 0;
94 
95     /**
96      * Hash a StringData in a way that respects this comparator.
97      */
hash(StringData stringToHash)98     size_t hash(StringData stringToHash) const {
99         size_t seed = 0;
100         hash_combine(seed, stringToHash);
101         return seed;
102     }
103 
104     /**
105      * Hash a StringData in a way that respects this comparator, and return the result in the 'seed'
106      * in-out parameter.
107      */
108     virtual void hash_combine(size_t& seed, StringData stringToHash) const = 0;
109 
110     /**
111      * Returns a function object which can evaluate string equality according to this comparator.
112      * This comparator must outlive the returned function object.
113      */
makeEqualTo()114     EqualTo makeEqualTo() const {
115         return EqualTo(this);
116     }
117 
118     /**
119      * Returns a function object which can hash strings according to this comparator. This
120      * comparator must outlive the returned function object.
121      */
makeHasher()122     Hasher makeHasher() const {
123         return Hasher(this);
124     }
125 
126     /**
127      * Construct an empty unordered set of StringData whose equivalence classes are given by this
128      * comparator. This comparator must outlive the returned set.
129      */
makeStringDataUnorderedSet()130     StringDataUnorderedSet makeStringDataUnorderedSet() const {
131         return StringDataUnorderedSet(0, makeHasher(), makeEqualTo());
132     }
133 
134     /**
135      * Construct an empty unordered map from StringData to type T whose equivalence classes are
136      * given by this comparator. This comparator must outlive the returned set.
137      */
138     template <typename T>
makeStringDataUnorderedMap()139     StringDataUnorderedMap<T> makeStringDataUnorderedMap() const {
140         return StringDataUnorderedMap<T>(0, makeHasher(), makeEqualTo());
141     }
142 };
143 
144 using StringDataUnorderedSet = StringData::ComparatorInterface::StringDataUnorderedSet;
145 
146 template <typename T>
147 using StringDataUnorderedMap = StringData::ComparatorInterface::StringDataUnorderedMap<T>;
148 
149 }  // namespace mongo
150