openttd.cpp

// [...]

Globals *_globals;

// [...]

class Globals { // <-- class type redefinition error
public:
	/* Public accessors */
	bool IsGameMode(GameMode mode)
	{
		return game_mode == mode;
	}

	void SetGameMode(GameMode mode)
	{
		game_mode = mode;
	}

	void BackupGameMode()
	{
		backup_game_mode = game_mode;
	}

	void RestoreGameMode()
	{
		game_mode = backup_game_mode;
	}

	GameMode GetGameMode()
	{
		return game_mode;
	}

	GameMode GetOldGameMode()
	{
		return backup_game_mode;
	}

private:
	GameMode game_mode;        ///< Current game mode
	GameMode backup_game_mode; ///< Backup game mode, used for brief game changes.
};

openttd.h

// [...]

class Globals {
public:
	static Globals *GetInstance()
	{
		if (!instance) {
			instance = new Globals();
		}

		return instance;
	}

	/* Public accessors */
	virtual bool IsGameMode(GameMode mode);
	virtual void SetGameMode(GameMode mode);
	virtual void BackupGameMode();
	virtual void RestoreGameMode();
	virtual GameMode GetGameMode();
	virtual GameMode GetOldGameMode();

private:
	static Globals *instance;
	Globals() {}
	Globals(Globals const&);
	Globals &operator=(const Globals&);
};

extern Globals *_globals;