C++11观察者模式

题目，

构造函数时subscribe,并notify
析构函数时unsubscribe,并notify。
纯粹的观察者模式。

代码如下，

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

struct IRat {
    int attack{1};
};

struct Game
{
    vector<IRat*> rats;
    
    void notify() {
        for(auto&& rat: rats)  {
            rat->attack = rats.size();
        }
    }
    
    void subscribe(IRat* rat) {
        rats.push_back(rat);
    }
    
    void unsubscribe(IRat* rat) {
        auto result = find(begin(rats), end(rats), rat);
        rats.erase(result);
    }
};

struct Rat : IRat
{
    Game& game;
    
    Rat(Game &game) : game(game)
    {
        game.subscribe(this);
        game.notify();
    }

    ~Rat() 
    { 
        game.unsubscribe(this);
        game.notify();
    }
};