c++ - Template based Subject Observer pattern - Should I use static_cast or dynamic_cast -

i referring article implementing subject/observer pattern templates

i did modification , became code follow.

template <class t, class a> class observer { public:     observer() {}     virtual ~observer() {}     virtual void update(t& subject, arg) = 0; };  template <class t, class a> class subject { public:     subject() {}     virtual ~subject() {}      // take note that, didn't make following functions virtual,     // not expect them overridden.     void attach(observer<t, a> &observer) {         // ensure no duplication.         std::vector<observer<t, a> *>::const_iterator iterator = std::find(observers.begin(), observers.end(), &observer);         if (iterator == observers.end()) {             observers.push_back(&observer);         }     }      void dettach(observer<t, a> &observer) {         std::vector<observer<t, a> *>::const_iterator iterator = std::find(observers.begin(), observers.end(), &observer);         if (iterator != observers.end()) {             observers.erase(iterator);         }     }      void dettachall() {         observers.clear();     }      void notify(a arg)     {         std::vector<observer<t, a> *>::const_iterator it;         (it = observers.begin(); != observers.end(); it++) {              (*it)->update(*(static_cast<t *>(this)), arg);         }     }  private:     std::vector<observer<t, a> *> observers; }; 

later, realize (*it)->update(*(static_cast<t *>(this)), arg); having limitation. example,

// cause compilation error in static_cast, cannot cast cat1 animal. class cat1 : public animal, public subject<animal, int> { public:     virtual void speak() {         notify(888);     } };  class zoo1 : public observer<animal, int> { public:     zoo1() {         c.attach(*this);         c.speak();     }      virtual void update(animal& subject, int arg) {         cout << "zoo1 received notification " << arg << endl;     }      cat1 c; }; 

i can solve problem changing static_cast dynamic_cast. however, not sure whether fall other traps? guess on author original intention in having static_cast, ensure type safety checking during compile time.

your problem come fact animal should subject not cat,

class animal : public subject<animal,int> {     ... };  class cat1 : public animal {     public:     virtual void speak()      {         notify(888);     } };  class zoo1 : public observer<animal, int> { public:     zoo1()      {         c.attach(*this);         c.speak();     }  virtual void update(animal& subject, int arg)      {         cout << "zoo1 received notification " << arg << endl;     }  cat1 c; }; 

by doing every subject static-cast "able" animal. not case cat1