observable.h

Think in C++ 2nd

//: C25:Observable.h
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// The Observable class
#ifndef OBSERVABLE_H
#define OBSERVABLE_H
#include "Observer.h"
#include <set>

class Observable {
  bool changed;
  std::set<Observer*> observers;
protected:
  virtual void setChanged() { changed = true; }
  virtual void clearChanged(){ changed = false; }
public:
  virtual void addObserver(Observer& o) {
    observers.insert(&o);
  }
  virtual void deleteObserver(Observer& o) {
    observers.erase(&o);
  }
  virtual void deleteObservers() {
    observers.clear();
  }
  virtual int countObservers() {
    return observers.size();
  }
  virtual bool hasChanged() { return changed; }
  // If this object has changed, notify all
  // of its observers:
  virtual void notifyObservers(Argument* arg=0) {
    if(!hasChanged()) return;
    clearChanged(); // Not "changed" anymore
    std::set<Observer*>::iterator it;
    for(it = observers.begin(); 
      it != observers.end(); it++)
      (*it)->update(this, arg);
  }
};
#endif // OBSERVABLE_H ///:~