1 /*
2 * Copyright (C) 2017 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #ifndef LIBTEXTCLASSIFIER_UTIL_GTL_MAP_UTIL_H_
18 #define LIBTEXTCLASSIFIER_UTIL_GTL_MAP_UTIL_H_
19
20 namespace libtextclassifier {
21
22 // Returns a const reference to the value associated with the given key if it
23 // exists, otherwise returns a const reference to the provided default value.
24 //
25 // WARNING: If a temporary object is passed as the default "value,"
26 // this function will return a reference to that temporary object,
27 // which will be destroyed at the end of the statement. A common
28 // example: if you have a map with string values, and you pass a char*
29 // as the default "value," either use the returned value immediately
30 // or store it in a string (not string&).
31 template <class Collection>
FindWithDefault(const Collection & collection,const typename Collection::value_type::first_type & key,const typename Collection::value_type::second_type & value)32 const typename Collection::value_type::second_type& FindWithDefault(
33 const Collection& collection,
34 const typename Collection::value_type::first_type& key,
35 const typename Collection::value_type::second_type& value) {
36 typename Collection::const_iterator it = collection.find(key);
37 if (it == collection.end()) {
38 return value;
39 }
40 return it->second;
41 }
42
43 // Inserts the given key and value into the given collection if and only if the
44 // given key did NOT already exist in the collection. If the key previously
45 // existed in the collection, the value is not changed. Returns true if the
46 // key-value pair was inserted; returns false if the key was already present.
47 template <class Collection>
InsertIfNotPresent(Collection * const collection,const typename Collection::value_type & vt)48 bool InsertIfNotPresent(Collection* const collection,
49 const typename Collection::value_type& vt) {
50 return collection->insert(vt).second;
51 }
52
53 // Same as above except the key and value are passed separately.
54 template <class Collection>
InsertIfNotPresent(Collection * const collection,const typename Collection::value_type::first_type & key,const typename Collection::value_type::second_type & value)55 bool InsertIfNotPresent(
56 Collection* const collection,
57 const typename Collection::value_type::first_type& key,
58 const typename Collection::value_type::second_type& value) {
59 return InsertIfNotPresent(collection,
60 typename Collection::value_type(key, value));
61 }
62
63 } // namespace libtextclassifier
64
65 #endif // LIBTEXTCLASSIFIER_UTIL_GTL_MAP_UTIL_H_
66