65 lines
2.6 KiB
C++
65 lines
2.6 KiB
C++
/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef LIBTEXTCLASSIFIER_UTIL_GTL_MAP_UTIL_H_
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#define LIBTEXTCLASSIFIER_UTIL_GTL_MAP_UTIL_H_
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namespace libtextclassifier {
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// Returns a const reference to the value associated with the given key if it
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// exists, otherwise returns a const reference to the provided default value.
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//
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// WARNING: If a temporary object is passed as the default "value,"
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// this function will return a reference to that temporary object,
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// which will be destroyed at the end of the statement. A common
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// example: if you have a map with string values, and you pass a char*
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// as the default "value," either use the returned value immediately
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// or store it in a string (not string&).
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template <class Collection>
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const typename Collection::value_type::second_type& FindWithDefault(
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const Collection& collection,
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const typename Collection::value_type::first_type& key,
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const typename Collection::value_type::second_type& value) {
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typename Collection::const_iterator it = collection.find(key);
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if (it == collection.end()) {
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return value;
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}
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return it->second;
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}
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// Inserts the given key and value into the given collection if and only if the
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// given key did NOT already exist in the collection. If the key previously
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// existed in the collection, the value is not changed. Returns true if the
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// key-value pair was inserted; returns false if the key was already present.
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template <class Collection>
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bool InsertIfNotPresent(Collection* const collection,
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const typename Collection::value_type& vt) {
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return collection->insert(vt).second;
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}
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// Same as above except the key and value are passed separately.
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template <class Collection>
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bool InsertIfNotPresent(
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Collection* const collection,
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const typename Collection::value_type::first_type& key,
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const typename Collection::value_type::second_type& value) {
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return InsertIfNotPresent(collection,
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typename Collection::value_type(key, value));
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}
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} // namespace libtextclassifier
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#endif // LIBTEXTCLASSIFIER_UTIL_GTL_MAP_UTIL_H_
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