Cplusplus-design-pattern/observer_coding_exercise_17.cpp at master · monicayyt/Cplusplus-design-pattern · GitHub

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

struct IRat
{
    virtual void rat_enters(IRat* sender) = 0;
    virtual void rat_dies(IRat* sender) = 0;
    virtual void notify(IRat* target) = 0;
};

struct Game
{
    vector<IRat*> rats;
    virtual void fire_rat_enters(IRat* sender)
    {
      for (auto rat : rats) rat->rat_enters(sender);
    }
    virtual void fire_rat_dies(IRat* sender)
    {
      for (auto rat : rats) rat->rat_dies(sender);
    }
    virtual void fire_notify(IRat* target)
    {
      for (auto rat : rats) rat->notify(target);
    }
};

struct Rat : IRat
{
    Game& game;
    int attack{1};

    Rat(Game &game) : game(game)
    {
      game.rats.push_back(this);
      game.fire_rat_enters(this);
    }

    ~Rat()
    {
      game.fire_rat_dies(this);
      game.rats.erase(std::remove(game.rats.begin(),game.rats.end(),this));
    }

    void rat_enters(IRat *sender) override {
      if (sender != this)
      {
        ++attack;
        game.fire_notify(sender);
      }
    }

    void rat_dies(IRat *sender) override {
      --attack;
    }

    void notify(IRat *target) override {
      if (target == this) ++attack;
    }
};