util/gtl/map_util.h

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef KNOWLEDGE_CEREBRA_SENSE_TEXT_CLASSIFIER_LIB2_UTIL_GTL_MAP_UTIL_H_
#define KNOWLEDGE_CEREBRA_SENSE_TEXT_CLASSIFIER_LIB2_UTIL_GTL_MAP_UTIL_H_

namespace libtextclassifier2 {

// Returns a const reference to the value associated with the given key if it
// exists, otherwise returns a const reference to the provided default value.
//
// WARNING: If a temporary object is passed as the default "value,"
// this function will return a reference to that temporary object,
// which will be destroyed at the end of the statement. A common
// example: if you have a map with string values, and you pass a char*
// as the default "value," either use the returned value immediately
// or store it in a string (not string&).
template <class Collection>
const typename Collection::value_type::second_type& FindWithDefault(
    const Collection& collection,
    const typename Collection::value_type::first_type& key,
    const typename Collection::value_type::second_type& value) {
  typename Collection::const_iterator it = collection.find(key);
  if (it == collection.end()) {
    return value;
  }
  return it->second;
}

// Inserts the given key and value into the given collection if and only if the
// given key did NOT already exist in the collection. If the key previously
// existed in the collection, the value is not changed. Returns true if the
// key-value pair was inserted; returns false if the key was already present.
template <class Collection>
bool InsertIfNotPresent(Collection* const collection,
                        const typename Collection::value_type& vt) {
  return collection->insert(vt).second;
}

// Same as above except the key and value are passed separately.
template <class Collection>
bool InsertIfNotPresent(
    Collection* const collection,
    const typename Collection::value_type::first_type& key,
    const typename Collection::value_type::second_type& value) {
  return InsertIfNotPresent(collection,
                            typename Collection::value_type(key, value));
}

}  // namespace libtextclassifier2

#endif  // KNOWLEDGE_CEREBRA_SENSE_TEXT_CLASSIFIER_LIB2_UTIL_GTL_MAP_UTIL_H_