feat(cmat): implement Ex41 observer pattern

Refactor the Pelican crossing exercise to use the Observer
pattern: Pelican acts as Subject and each Pole observes it,
replacing direct calls through the owned Pole pointer.

Co-authored-by: Qwen 3.8 27B <qwen3.8_27b-q3_k_xl@lmstudio.local>

cmat/Ex41/Observer.h

@@ -4,7 +4,7 @@
 
 class Observer {
   public:
-    // TODO: declare the pure virtual function update()
+      virtual void update() = 0;
 };
 
 #endif

cmat/Ex41/Pelican.cpp

@@ -3,29 +3,25 @@
 #include "PelicanTimer.h"
 #include "Pole.h"
 
-Pelican::Pelican(int x, int y)
+Pelican::Pelican()
-    : pressed(false), RED_TIME(4), YELLOW_TIME(2), GREEN_TIME(3), FLASH_TIME(5), myPole(new Pole(x, y)),
+    : pressed(false), RED_TIME(4), YELLOW_TIME(2), GREEN_TIME(3), FLASH_TIME(5),
       state(GREEN_IDLE) {
     myTimer = new PelicanTimer(*this, &Pelican::timerExpired);
 
-    myPole->setTrafficLights(getState());
+    notify();
-    myPole->setWaitLight(isPressed());
 }
 
-Pelican::~Pelican() { delete myPole; }
+Pelican::~Pelican() { }
 
 void Pelican::press(void) {
     if (state == GREEN_IDLE) {
         state = YELLOW_STATE;
         myTimer->timeoutRequest(YELLOW_TIME);
         pressed = true;
-        myPole->setTrafficLights(getState());
-        myPole->setWaitLight(isPressed());
     } else if (state != RED_STATE) {
         pressed = true;
-        myPole->setTrafficLights(getState());
-        myPole->setWaitLight(isPressed());
     }
+    notify();
 }
 
 void Pelican::timerExpired(void) {
@@ -60,6 +56,5 @@ void Pelican::timerExpired(void) {
         break;
     }
 
-    myPole->setTrafficLights(getState());
+    notify();
-    myPole->setWaitLight(isPressed());
 }

cmat/Ex41/Pelican.h

@@ -7,12 +7,14 @@
 #ifndef PELICAN_H
 #define PELICAN_H
 
+#include "Subject.h"
+
 class PelicanTimer;
 class Pole;
 
-class Pelican {
+class Pelican : public Subject {
   public:
-    Pelican(int x, int y);
+    Pelican();
     ~Pelican();
 
     // call when the WAIT button has been pressed
@@ -39,8 +41,6 @@ class Pelican {
     // indicates whether the WAIT light should be on
     bool pressed;
 
-    Pole *myPole;
-
     // Timer that indicates when the lights should change
     PelicanTimer *myTimer;
 

cmat/Ex41/Pole.cpp

@@ -1,8 +1,9 @@
 #include "Pole.h"
 #include "Screen.h"
 
-Pole::Pole(int x, int y) : waitLight(new Light("WAIT", x + 6, y + 12, Screen::WHITE)) {
+Pole::Pole(int x, int y, Pelican& pelican) : waitLight(new Light("WAIT", x + 6, y + 12, Screen::WHITE)), pelican(pelican) {
     using namespace Screen; // we will discuss namespaces in the course
+    pelican.attach(this);
 
     lights[RED_LIGHT] = new Light("*", x + 11, y + 3, RED);
     lights[RED_MAN] = new Light("*<-=", x + 6, y + 4, RED);
@@ -57,3 +58,8 @@ void Pole::setTrafficLights(Pelican::PelicanState state) {
 }
 
 void Pole::setWaitLight(bool pressed) { waitLight->set(pressed ? Light::ON : Light::OFF); }
+
+void Pole::update() {
+    setTrafficLights(pelican.getState());
+    setWaitLight(pelican.isPressed());
+}

cmat/Ex41/Pole.h

@@ -3,22 +3,25 @@
 #define POLE_H
 
 #include "Light.h"
+#include "Observer.h"
 #include "Pelican.h"
 
-class Pole {
+class Pole : public Observer {
   public:
-    Pole(int x, int y);
+    Pole(int x, int y, Pelican&);
     ~Pole();
 
     void setTrafficLights(Pelican::PelicanState state);
     void setWaitLight(bool pressed);
 
+    void update();
+
   private:
     enum LightName { RED_LIGHT, YELLOW_LIGHT, GREEN_LIGHT, GREEN_MAN, RED_MAN };
 
     Light *lights[RED_MAN + 1];
-
     Light *waitLight;
+    Pelican& pelican;
 };
 
 #endif

cmat/Ex41/Subject.cpp

@@ -1,8 +1,12 @@
-
-
 #include "Subject.h"
 #include "Observer.h"
 
-// TODO: Implement the Subject::attach() member function that adds an Observer to the set
+void Subject::attach(Observer* observer) {
+    m_observers.insert(observer);
+}
 
-// TODO: Implement the Subject::notify() member function that calls all the update functions
+void Subject::notify() {
+    for (auto* observer : m_observers) {
+        observer->update();
+    }
+}

cmat/Ex41/Subject.h

@@ -8,11 +8,11 @@ class Observer;
 
 class Subject {
   public:
-    // TODO: Declare the attach() function that adds an Observer to the set
+    void attach(Observer* observer);
   protected:
-    // TODO: Declare the notify() function that calls all the update functions
+    void notify();
   private:
-    // TODO: Define a set of Observer pointers
+    std::set<Observer*> m_observers;
 };
 
 #endif

cmat/Ex41/main.cpp

@@ -1,13 +1,16 @@
 
 #include "Keyboard.h"
 #include "Pelican.h"
+#include "Pole.h"
 #include "TimerSet.h"
 
 #include <cctype> // provides toupper()
 
 int main() {
     Keyboard kbd;
-    Pelican thePelican(30, 0);
+    Pelican thePelican;
+    Pole pole1(20, 0, thePelican);
+    Pole pole2(40, 0, thePelican);
 
     char c = 0;