paperscissorsrock.cpp

Think in C++ 第二版源码

//: C25:PaperScissorsRock.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 1999
// Copyright notice in Copyright.txt
// Demonstration of multiple dispatching
#include "../purge.h"
#include <iostream>
#include <vector>
#include <algorithm>
#include <cstdlib>
#include <ctime>
using namespace std;

class Paper;
class Scissors;
class Rock;

enum Outcome { win, lose, draw };

ostream& 
operator<<(ostream& os, const Outcome out) {
  switch(out) {
    default:
    case win: return os << "win";
    case lose: return os << "lose";
    case draw: return os << "draw";
  }
}

class Item {
public:
  virtual Outcome compete(const Item*) = 0;
  virtual Outcome eval(const Paper*) const = 0;
  virtual Outcome eval(const Scissors*) const= 0;
  virtual Outcome eval(const Rock*) const = 0;
  virtual ostream& print(ostream& os) const = 0;
  virtual ~Item() {}
  friend ostream& 
  operator<<(ostream& os, const Item* it) {
    return it->print(os);
  }
};

class Paper : public Item {
public:
  Outcome compete(const Item* it) {
    return it->eval(this);
  }
  Outcome eval(const Paper*) const {
    return draw;
  }
  Outcome eval(const Scissors*) const {
    return win;
  }
  Outcome eval(const Rock*) const {
    return lose;
  }
  ostream& print(ostream& os) const {
    return os << "Paper   ";
  }
};

class Scissors : public Item {
public:
  Outcome compete(const Item* it) {
    return it->eval(this);
  }
  Outcome eval(const Paper*) const {
    return lose;
  }
  Outcome eval(const Scissors*) const {
    return draw;
  }
  Outcome eval(const Rock*) const {
    return win;
  }
  ostream& print(ostream& os) const {
    return os << "Scissors";
  }
};

class Rock : public Item {
public:
  Outcome compete(const Item* it) {
    return it->eval(this);
  }
  Outcome eval(const Paper*) const {
    return win;
  }
  Outcome eval(const Scissors*) const {
    return lose;
  }
  Outcome eval(const Rock*) const {
    return draw;
  }
  ostream& print(ostream& os) const {
    return os << "Rock    ";
  }
};

struct ItemGen {
  ItemGen() { srand(time(0)); }
  Item* operator()() {
    switch(rand() % 3) {
      default:
      case 0:
        return new Scissors();
      case 1:
        return new Paper();
      case 2:
        return new Rock();
    }
  }
};

struct Compete {
  Outcome operator()(Item* a, Item* b) {
    cout << a << "\t" << b << "\t";
    return a->compete(b);
  }
};

int main() {
  const int sz = 20;
  vector<Item*> v(sz*2);
  generate(v.begin(), v.end(), ItemGen());
  transform(v.begin(), v.begin() + sz, 
    v.begin() + sz, 
    ostream_iterator<Outcome>(cout, "\n"), 
    Compete());
  purge(v);
} ///:~