reply to /u/TheGoodPlaceJanet

Lamp.cpp

class UsbLampManager : public LampManager
{
  bool switch_lamp(bool turn_on) override; 
};

class BluetoothLampManager : public LampManager
{
  bool switch_lamp(bool turn_on) override; 
};

class Lamp
{
public:
   Lamp(LampManager* mng ) : manager_ptr_(mng){ assert(manager_ptr_ != nullptr); }
   bool turn_lamp_on() { manager_ptr_->switch_lamp(true); }
   bool turn_lamp_off() { manager_ptr_->switch_lamp(false); }
private:
   LampManager* manager_ptr_;
};

void foo()
{
   UsbLampManager usb_lamp_manager;
   BluetoothLampManager bluethoot_lamp_manager;
   
   Lamp lamp_a(&usb_lamp_manager);
   Lamp lamp_b(&bluethoot_lamp_manager);


   lamp_b->turn_lamp_on();
}