模板参数tag的用法

//通过结构体/类的类型来作为模板参数的tag，
//用来区分tag之间的区别。
//made by davidsu33
//例如对于某个全局的静态变量，你如果希望有
//很多份，但是其实现又是一样的，你可以考虑
//以模板的形式，通过类tag来区分

//而且还可以根据实际需要来特化模板

#include "stdafx.h"
#include <iostream>
#include <cassert>

using namespace std;

template<class Tag> class Instance;

template<class Tag>
class Instance
{
public:
	~Instance(){};

	static Instance &getInstance()
	{
		static Instance  s_instance;
		return s_instance;
	}

	void doOne()
	{
		cout<<"do One"<<endl;
	}

	void doTwo()
	{
		cout<<"do Two"<<endl;
	}

private:
	Instance(){};
	Instance& operator=(const Instance&);
	Instance(const Instance&);
};

struct TagOne{};
struct TagTwo{};
struct TagThree{};

typedef Instance<TagOne> InstanceOne;
typedef Instance<TagTwo> InstanceTwo;

template<>
class Instance<TagThree>
{
public:
	void doOne()
	{
		cout<<"do Three"<<endl;
	}

	void doTwo()
	{
		cout<<"do Three"<<endl;
	}
};

void test_instance()
{
	InstanceOne &one = InstanceOne::getInstance();
	InstanceTwo &two = InstanceTwo::getInstance();

	void* ptrOne = static_cast<void*>(&one);
	void *ptrTwo = static_cast<void*>(&two);

	assert(ptrOne != ptrTwo);

	Instance<TagThree> three1, three2, three;
	three.doOne();
	three.doTwo();
}

int _tmain(int argc, _TCHAR* argv[])
{
	test_instance();

	getchar();
	return 0;
}

模板参数tag的用法,布布扣,bubuko.com