[tutorial] Observer pattern

#include <iostream>
#include <vector>
using namespace std;

class Subject
{

public:
    vector < class Observer* > views;
    int value;

    void attach(Observer* obs)
    {
        views.push_back(obs);
    }

    void detach_back()
    {
        views.pop_back();
    }

    void setVal(int val)
    {
        value = val;
        notify();
    }
    int getVal()
    {
        return value;
    }
    void notify();


};

class Observer
{


public:
    Observer(Subject* mod, int div)
    {
        model = mod;
        denom = div;
        model->attach(this);
    }
    virtual void update() = 0;

    Subject* model;
    int denom;

protected:
    Subject* getSubject()
    {
        return model;
    }
    int getDivisor()
    {
        return denom;
    }
};

void Subject::notify()
{
    // 5. Publisher broadcasts
    for (int i = 0; i < views.size(); i++)
        views[i]->update();
}

class DivObserver : public Observer
{
public:
    DivObserver(Subject* mod, int div) : Observer(mod, div) {}
    void update()
    {
        // 6. "Pull" information of interest
        int v = getSubject()->getVal(), d = getDivisor();
        cout << v << " div " << d << " is " << v / d << '\n';
    }
};

class ModObserver : public Observer
{
public:
    ModObserver(Subject* mod, int div) : Observer(mod, div) {}
    void update()
    {
        int v = getSubject()->getVal(), d = getDivisor();
        cout << v << " mod " << d << " is " << v % d << '\n';
    }
};

int main()
{
    Subject subj;
    DivObserver divObs1(&subj, 4); // 7. Client configures the number and
    DivObserver divObs2(&subj, 3); //    type of Observers
    ModObserver modObs3(&subj, 3);
    subj.setVal(14);

    subj.detach_back();
    subj.setVal(15);
}