text: // Ceres Solver - A fast non-linear least squares minimizer
  // Copyright 2015 Google Inc. All rights reserved.
  // http://ceres-solver.org/
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are met:
  //
  // * Redistributions of source code must retain the above copyright notice,
  //   this list of conditions and the following disclaimer.
  // * Redistributions in binary form must reproduce the above copyright notice,
  //   this list of conditions and the following disclaimer in the documentation
  //   and/or other materials provided with the distribution.
  // * Neither the name of Google Inc. nor the names of its contributors may be
  //   used to endorse or promote products derived from this software without
  //   specific prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  // ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
  // LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
  // CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
  // SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
  // CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
  // ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  // POSSIBILITY OF SUCH DAMAGE.
  //
  // Author: keir@google.com (Keir Mierle)
  //
  // Originally by Anton Carver
  
  #ifndef CERES_INTERNAL_MAP_UTIL_H_
  #define CERES_INTERNAL_MAP_UTIL_H_
  
  #include <utility>
  #include "ceres/internal/port.h"
  #include "glog/logging.h"
  
  namespace ceres {
  
  // Perform a lookup in a map or hash_map, assuming that the key exists.
  // Crash if it does not.
  //
  // This is intended as a replacement for operator[] as an rvalue (for reading)
  // when the key is guaranteed to exist.
  //
  // operator[] is discouraged for several reasons:
  //  * It has a side-effect of inserting missing keys
  //  * It is not thread-safe (even when it is not inserting, it can still
  //      choose to resize the underlying storage)
  //  * It invalidates iterators (when it chooses to resize)
  //  * It default constructs a value object even if it doesn't need to
  //
  // This version assumes the key is printable, and includes it in the fatal log
  // message.
  template <class Collection>
  const typename Collection::value_type::second_type&
  FindOrDie(const Collection& collection,
            const typename Collection::value_type::first_type& key) {
    typename Collection::const_iterator it = collection.find(key);
    CHECK(it != collection.end()) << "Map key not found: " << key;
    return it->second;
  }
  
  // Perform a lookup in a map or hash_map.
  // If the key is present in the map then the value associated with that
  // key is returned, otherwise the value passed as a default is returned.
  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;
  }
  
  // Insert a new key and value into a map or hash_map.
  // If the key is not present in the map the key and value are
  // inserted, otherwise nothing happens. True indicates that an insert
  // took place, false indicates the key was already present.
  template <class Collection>
  bool InsertIfNotPresent(
      Collection * const collection,
      const typename Collection::value_type::first_type& key,
      const typename Collection::value_type::second_type& value) {
    std::pair<typename Collection::iterator, bool> ret =
        collection->insert(typename Collection::value_type(key, value));
    return ret.second;
  }
  
  // Perform a lookup in a map or hash_map.
  // Same as above but the returned pointer is not const and can be used to change
  // the stored 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;
  }
  
  // Test to see if a set, map, hash_set or hash_map contains a particular key.
  // Returns true if the key is in the collection.
  template <class Collection, class Key>
  bool ContainsKey(const Collection& collection, const Key& key) {
    typename Collection::const_iterator it = collection.find(key);
    return it != collection.end();
  }
  
  // Inserts a new key/value into a map or hash_map.
  // Dies if the key is already present.
  template<class Collection>
  void InsertOrDie(Collection* const collection,
                   const typename Collection::value_type::first_type& key,
                   const typename Collection::value_type::second_type& data) {
    typedef typename Collection::value_type value_type;
    CHECK(collection->insert(value_type(key, data)).second)
      << "duplicate key: " << key;
  }
  
  }  // namespace ceres
  
  #endif  // CERES_INTERNAL_MAP_UTIL_H_
  