internal/ceres/map_util.h

// Ceres Solver - A fast non-linear least squares minimizer
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// http://ceres-solver.org/
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// 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/export.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) {
  using value_type = typename Collection::value_type;
  CHECK(collection->insert(value_type(key, data)).second)
      << "duplicate key: " << key;
}

}  // namespace ceres

#endif  // CERES_INTERNAL_MAP_UTIL_H_