设计模式 之美 -- 策略模式

策略模式作为行为型设计模式中的一种，主要封装相同功能的不同实现算法，用于在用户程序内部灵活切换。对用户来说能够快速替换对应的算法，能够让算法的实现独立于使用的用户。

基本的UML类图如下：

#include <iostream>
#include <string>

using namespace std;

class Cache {
public:
    virtual void use_cache() = 0;
    virtual ~Cache(){}
};

class LRU: public Cache {
public:
    LRU(){}
    void use_cache() {
        cout << "Use LRU Cache " << endl;
    }

};

class Clock: public Cache {
public:
    Clock(){}
    void use_cache() {
        cout << "Use Clock Cache " << endl;
    }

};

class Strategy {
public:
    //explicit Strategy(Cache *cache, string name): _cache(cache),res(name) {}
    Strategy(Cache *cache, string name): _cache(cache),res(name) {}

    void set_cache(Cache *cache) {
        this -> _cache = cache;
    }
    void use_cache() {
        cout << "strategy name is : "<< res << endl;
        _cache->use_cache(); 
    }

private:
    Cache *_cache;
    string res;
};

int main() {
    LRU *caheA = new LRU();
    Clock *caheB = new Clock();

    Strategy stra(caheA, "stra");
    Strategy strb(caheB, "strb");

    stra.use_cache();
    strb.use_cache();

    cout << "Change the strategy Quickly" << endl;
    stra.set_cache(caheB);
    strb.set_cache(caheA);

    stra.use_cache();
    strb.use_cache();
    return 0;
}      

strategy name is : stra
Use LRU Cache
strategy name is : strb
Use Clock Cache
Change the strategy Quickly
strategy name is : stra
Use Clock Cache
strategy name is : strb
Use LRU Cache