Another aspect of the Mach5 Engine that uses the State pattern is the M5StageManager class:

class M5StageManager 
{ 
public: 
  friend class M5App; 
 
  //Registers a GameStage and a builder with the the StageManger 
  static void AddStage(M5StageTypes type, M5StageBuilder* builder); 
  //Removes a Stage Builder from the Manager 
  static void RemoveStage(M5StageTypes type); 
  //Clears all stages from the StageManager 
  static void ClearStages(void); 
  //Sets the given stage ID to the starting stage of the game 
  static void SetStartStage(M5StageTypes startStage); 
  //Test if the game is quitting 
  static bool IsQuitting(void); 
  //Test stage is restarting 
  static bool IsRestarting(void); 
  //Gets the pointer to the users game specific data 
  static M5GameData& GetGameData(void); 
  //Sets the next stage for the game 
  static void SetNextStage(M5StageTypes nextStage); 
  // Pauses the current stage, so it can be resumed but changes stages 
  static void PauseAndSetNextStage(M5StageTypes nextStage); 
  // Resumes the previous stage 
  static void Resume(void); 
  //Tells the game to quit 
  static void Quit(void); 
  //Tells the stage to restart 
  static void Restart(void); 
private: 
  static void Init(const M5GameData& gameData, int framesPerSecond);
  static void Update(void); 
  static void Shutdown(void); 
  static void InitStage(void); 
  static void ChangeStage(void); 
 
};//end M5StageManager 

Since there will only be one of these in the game, all of the functionality has been made static similarly to a Singleton but, depending on the state that the project is in, it will do different things. Take, for example, changing what stage we are in. I'm sure you'll find that it looks very similar to how we changed states earlier:

void M5StageManager::ChangeStage(void)
{
 /*Only unload if we are not restarting*/
 if (s_isPausing)
 {
   M5ObjectManager::Pause();
   M5Phy::Pause();
   M5Gfx::Pause(s_drawPaused);
   PauseInfo pi(s_pStage, s_currStage);
   s_pauseStack.push(pi);
   s_isPausing = false;
 }
 else if (s_isResuming)
 {
   /*Make sure to shutdown the stage*/
   s_pStage->Shutdown();
   delete s_pStage;
   s_pStage = nullptr;
 }
 else if (!s_isRestarting) //Just changine the stage
 {
   /*Make sure to shutdown the stage*/
   s_pStage->Shutdown();
   delete s_pStage;
   s_pStage = nullptr;

   //If we are setting the next state, that means we are ignore all
   //paused states, so lets clear the pause stack
   while (!s_pauseStack.empty())
   {
     M5Gfx::Resume();
     M5Phy::Resume();
     M5ObjectManager::Resume();
     PauseInfo pi = s_pauseStack.top();
     pi.pStage->Shutdown();
     delete pi.pStage;
     s_pauseStack.pop();
   }

 }
 else if (s_isRestarting)
 {
   /*Make sure to shutdown the stage*/
   s_pStage->Shutdown();
 }

 s_currStage = s_nextStage;
}

I highly advise taking a closer look at the file and going through each function to see how they interact with each other.