text: /* Copyright 2015 The TensorFlow Authors. All Rights Reserved.
  
  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.
  ==============================================================================*/
  
  // This file provides utility functions for use with STL map-like data
  // structures, such as std::map and hash_map. Some functions will also work with
  // sets, such as ContainsKey().
  
  #ifndef TENSORFLOW_LIB_GTL_MAP_UTIL_H_
  #define TENSORFLOW_LIB_GTL_MAP_UTIL_H_
  
  #include <stddef.h>
  #include <iterator>
  #include <memory>
  #include <string>
  #include <utility>
  
  namespace tensorflow {
  namespace gtl {
  
  // Returns a pointer to the const value associated with the given key if it
  // exists, or NULL otherwise.
  template <class Collection>
  const typename Collection::value_type::second_type* FindOrNull(
      const Collection& collection,
      const typename Collection::value_type::first_type& key) {
    typename Collection::const_iterator it = collection.find(key);
    if (it == collection.end()) {
      return 0;
    }
    return &it->second;
  }
  
  // Same as above but returns a pointer to the non-const value.
  template <class Collection>
  typename Collection::value_type::second_type* FindOrNull(
      Collection& collection,  // NOLINT
      const typename Collection::value_type::first_type& key) {
    typename Collection::iterator it = collection.find(key);
    if (it == collection.end()) {
      return 0;
    }
    return &it->second;
  }
  
  // Returns the pointer value associated with the given key. If none is found,
  // NULL is returned. The function is designed to be used with a map of keys to
  // pointers.
  //
  // This function does not distinguish between a missing key and a key mapped
  // to a NULL value.
  template <class Collection>
  typename Collection::value_type::second_type FindPtrOrNull(
      const Collection& collection,
      const typename Collection::value_type::first_type& key) {
    typename Collection::const_iterator it = collection.find(key);
    if (it == collection.end()) {
      return typename Collection::value_type::second_type();
    }
    return it->second;
  }
  
  // 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-value pair into the collection. Returns true if and
  // only if the key from the given pair didn't previously exist. Otherwise, the
  // value in the map is replaced with the value from the given pair.
  template <class Collection>
  bool InsertOrUpdate(Collection* const collection,
                      const typename Collection::value_type& vt) {
    std::pair<typename Collection::iterator, bool> ret = collection->insert(vt);
    if (!ret.second) {
      // update
      ret.first->second = vt.second;
      return false;
    }
    return true;
  }
  
  // Same as above, except that the key and value are passed separately.
  template <class Collection>
  bool InsertOrUpdate(Collection* const collection,
                      const typename Collection::value_type::first_type& key,
                      const typename Collection::value_type::second_type& value) {
    return InsertOrUpdate(collection,
                          typename Collection::value_type(key, value));
  }
  
  // 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));
  }
  
  // Looks up a given key and value pair in a collection and inserts the key-value
  // pair if it's not already present. Returns a reference to the value associated
  // with the key.
  template <class Collection>
  typename Collection::value_type::second_type& LookupOrInsert(
      Collection* const collection, const typename Collection::value_type& vt) {
    return collection->insert(vt).first->second;
  }
  
  // Same as above except the key-value are passed separately.
  template <class Collection>
  typename Collection::value_type::second_type& LookupOrInsert(
      Collection* const collection,
      const typename Collection::value_type::first_type& key,
      const typename Collection::value_type::second_type& value) {
    return LookupOrInsert(collection,
                          typename Collection::value_type(key, value));
  }
  
  }  // namespace gtl
  }  // namespace tensorflow
  
  #endif  // TENSORFLOW_LIB_GTL_MAP_UTIL_H_
  