C++设计模式---策略模式

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定义算法家族，分别封装起来，让他们之间可以相互替换，让算法变化，不会影响到用户。适合类中的成员以方法为主，算法经常变动，简化了单元测试（因为每个算法都有自己的类），可以通过自己的借口单独测试。策略模式和简单工厂模式基本相同，但简单工厂模式只能解决对象创建问题，对于经常变动的算法应该使用策略模式。

//策略模式
class Arithmetic
{
public:
	virtual void Replace() = 0;
};
//三种具体的替换算法  
class Arithmetic_A : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic A" << endl; }
};

class Arithmetic_B : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic B" << endl; }
};
class Arithmetic_C : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic C" << endl; }
};
//Cache需要用到替换算法  
class Cache
{
private:
	Arithmetic * ar;
public:
	Cache(Arithmetic *temp) { ar = temp; }
	~Cache() { delete ar; }
	void Replace() { ar->Replace(); }
};

int main()
{
	Cache *cache = new Cache(new Arithmetic_A);//暴露了算法的定义  
	cache->Replace();

	Cache *cache_1 = new Cache(new Arithmetic_B);//暴露了算法的定义  
	cache_1->Replace();

	Cache *cache_2 = new Cache(new Arithmetic_C);//暴露了算法的定义  
	cache_2->Replace();

	return 0;
}

策略模式与工厂模式结合：客户端只需访问Cache类，而不用知道其他任何信息，只需要知道算法的标签就行了，实现了低耦合。

enum CTYPE {RA, RB ,RC};
//策略模式
class Arithmetic
{
public:
	virtual void Replace() = 0;
};
//三种具体的替换算法  
class Arithmetic_A : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic A" << endl; }
};

class Arithmetic_B : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic B" << endl; }
};
class Arithmetic_C : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic C" << endl; }
};
//Cache需要用到替换算法  
class Cache
{
private:
	Arithmetic * ar;
public:
	Cache(CTYPE temp) 
	{ 
		if (temp == RA)
			ar = new Arithmetic_A();
		else if (temp == RB)
			ar = new Arithmetic_B();
		else if (temp == RC)
			ar = new Arithmetic_C();
		else
			ar = NULL;
	}
	~Cache() { delete ar; }
	void Replace() { ar->Replace(); }
};

int main()
{
	Cache *cache = new Cache(RA);//Cache cache(RA); cache.Replace();
	cache->Replace();
	Cache *cache_1 = new Cache(RB);  
	cache_1->Replace();
	Cache *cache_2 = new Cache(RC);  
	cache_2->Replace();

	return 0;
}

不需要传参数，直接调用指定算法

//策略模式
class Arithmetic
{
public:
	virtual void Replace() = 0;
};
//三种具体的替换算法  
class Arithmetic_A : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic A" << endl; }
};

class Arithmetic_B : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic B" << endl; }
};
class Arithmetic_C : public Arithmetic
{
public:
	void Replace() { cout << "Arithmetic C" << endl; }
};

template <class ARI>
class Cache
{
private:
	ARI ar;
public:
	Cache(){}
	~Cache() {}
	void Replace() { ar.Replace(); }
};

int main()
{
	Cache<Arithmetic_B> cache; //模板实参
	cache.Replace();
	return 0;
}

策略模式图