http://codereview.stackexchange.com/questions/109750/is-this-the-correct-way-to-use-raii-for-a-map-of-references

main.cpp

#include <string>
#include <map>
#include <sstream>
#include <iostream>

class Room {
public:
  explicit Room(int id, const std::string& name) : m_id(id), m_name(name) {}
  const std::string& GetName() const { return m_name; }
  const int& GetEnterCount() const { return m_enterCount; };
  void OnEnter() { ++m_enterCount; }
  std::string GetRoomDescription();
private:
  std::string m_name; // should this be const?
  int m_id; // should this be const?
  int m_enterCount = 0;
};

std::string Room::GetRoomDescription()
{
  // What's the lifetime of "result"?
  // In C, this would be stack-allocated and dead
  // when the function returns.
  std::stringstream result;
  result << "ID: " << m_id << " - Name: " << m_name;
  return result.str();
}

class RoomList {
public:
  RoomList();
  ~RoomList() = default; // Is this needed? Rule of three?
  RoomList(const RoomList&) = delete; // Don't want copies
  RoomList& operator=(RoomList const&) = delete;
  const Room& GetRoom(int index);
private:
  // Should this be <int, Room> or <int, Room&>?
  std::map<int, Room> m_rooms;
};

RoomList::RoomList() {
  // Read all the rooms, e.g., from a data file
  // What is the lifetime of the Room I'm creating?
  // Room doesn't have copy or move ctors
  // Also, I'm not initializing m_rooms - what is its lifetime?
  m_rooms.emplace(0, Room(0, "Start Room"));
}

// Returning a reference to const Room - no one should be able to modify Room, except by calling room.OnEnter()
// room.OnEnter() should modify the Room inside the map (Individual Rooms are basically Singletons)
const Room& RoomList::GetRoom(int index) {
  auto result = m_rooms.find(index);
  if(result != m_rooms.end())
  {
    // result is a local var - is result->second valid after return?
    return result->second;
  }

  // Considering Optional<Room>
  // https://github.com/akrzemi1/Optional/
  throw "Invalid Index";
}

int main() {
  RoomList rooms;
  auto room = rooms.GetRoom(0);
  std::cout << "Name: " << room.GetName() << std::endl;
  std::cout << "Room: " << room.GetRoomDescription() << std::endl;
  std::cout << "Enter Count before: " << room.GetEnterCount() << std::endl;
  room.OnEnter();
  std::cout << "Enter Count after: " << room.GetEnterCount() << std::endl;
  return 0;
}