Singleton

• Singleton: A class of which only a single instance can exist. Ensure a class only has one instance, and provide a global point of access to it.
• Don’t need fig, just remember implementation. One class, two static, three access levels(private, protect, public)
  class Singleton{ 
  private: 
     static Singleton * m_instance; 
  protect 
     Singleton(); 
  public: 
    static getInstance(); 
  } 
   
  Singleton* Singleton::m_instance = nullptr; 
  Singleton::getInstance(){ 
    if(m_instance == nullptr) 
       m_instance = new Singleton(); 
     return m_instance; 
  }