Function InsertKeysFromMap

be/src/gutil/map-util.h:799–806

// Note: any initial contents of the key_container are not cleared.
template <class MapContainer, class KeyContainer>
void InsertKeysFromMap(const MapContainer& map_container,
                       KeyContainer* key_container) {
  CHECK(key_container != NULL);
  for (typename MapContainer::const_iterator it = map_container.begin();
       it != map_container.end(); ++it) {
    key_container->insert(it->first);
  }
}

// Appends all the keys from map_container into key_container, which must
// support push_back(MapContainer::key_type).