c++11 改进设计模式 Singleton模式

关于学习 《深入应用c++11》的代码笔记:

c++11之前是这么实现的

template<typename T>
class Singleton{
public:
	static T* Instance(){
		if (m_pInstance == nullptr)
			m_pInstance = new T();
		return m_pInstance;
	}

	template<typename T0>
	static T* Instance(T0 arg0){
		if (m_pInstance == nullptr)
			m_pInstance = new T(arg0);
		return m_pInstance;
	}
	
	template<typename T0,typename T1>
	static T* Instance(T0 arg0, T1 arg1){
		if (m_pInstance == nullptr)
			m_pInstance = new T(arg0, arg1);
		return m_pInstance;
	}

	template<typename T0, typename T1,typename T2>
	static T* Instance(T0 arg0, T1 arg1,T2 arg2){
		if (m_pInstance == nullptr)
			m_pInstance = new T(arg0, arg1,arg2);
		return m_pInstance;
	}

	template<typename T0, typename T1, typename T2,typename T3>
	static T* Instance(T0 arg0, T1 arg1, T2 arg2,T3 arg3){
		if (m_pInstance == nullptr)
			m_pInstance = new T(arg0, arg1, arg2,arg3);
		return m_pInstance;
	}

	template<typename T0, typename T1, typename T2, typename T3,typename T4>
	static T* Instance(T0 arg0, T1 arg1, T2 arg2, T3 arg3,T4 arg4){
		if (m_pInstance == nullptr)
			m_pInstance = new T(arg0, arg1, arg2, arg3,arg4);
		return m_pInstance;
	}

	template<typename T0, typename T1, typename T2, typename T3, typename T4,typename T5>
	static T* Instance(T0 arg0, T1 arg1, T2 arg2, T3 arg3, T4 arg4,T5 arg5){
		if (m_pInstance == nullptr)
			m_pInstance = new T(arg0, arg1, arg2, arg3, arg4,arg5);
		return m_pInstance;
	}

	static T* GetInstance()
	{
		if (m_pInstance == nullptr)
			throw std::logic_error("the instance is not init,please init the instance first");
			
		return m_pInstance;
	}

	static void DestroyInstance(){
		delete m_pInstance;
		m_pInstance = nullptr;
	}

private:
	Singleton(void);
	virtual ~Singleton(void);
	Singleton(const Singleton&);
	Singleton& operator = (const Singleton);

	static T* m_pInstance;
};

template<class T> T* Singleton<T>::m_pInstance = nullptr;

//============================================
struct A{
	A(){}
};

struct B{
	B(int x){}
};

struct C{
	C(int x, double y){}
};

int _tmain(int argc, _TCHAR* argv[])
{
	Singleton<A>::Instance();
	Singleton<A>::Instance();
	Singleton<B>::Instance(1);
	Singleton<C>::Instance(1,3.14);

	Singleton<A>::DestroyInstance();
	Singleton<B>::DestroyInstance();
	Singleton<C>::DestroyInstance();

	return 0;
}

　　c++11之后可以简略一点，使用了可变模板参数

template<typename T>
class Singleton{
public:
	template <typename... Args>
	static T* Instance(Args&&... args){
		if (m_pInstance == nullptr)
			m_pInstance = new T(std::forward<Args>(args)...);
		return m_pInstance;
	}

	static T* GetInstance(){
		if (m_pInstance == nullptr)
			throw std::logic_error("the instance is not init,please initialize the instance first");
		return m_pInstance;
	}

	static void DestroyInstance()
	{
		delete m_pInstance;
		m_pInstance = nullptr;
	}

private:
	Singleton(void);
	virtual ~Singleton(void);
	Singleton(const Singleton&);
	Singleton& operator=(const Singleton&);
private:
	static T* m_pInstance;
};

template<class T>T* Singleton<T>::m_pInstance = nullptr;

#include <iostream>
#include <string>

using namespace std;

struct A{
	A(const string&){ cout << "lvalue" << endl; }
	A(string&&x){ cout << "rvalue" << endl; }
};

struct B{
	B(const string&){ cout << "lvalue" << endl; }
	B(string&& x){ cout << "rvalue" << endl; }
};

struct C{
	C(int x, double y){}
	void Fun(){ cout << "Test" << endl; }
}; 


int _tmain(int argc, _TCHAR* argv[])
{
	string str = "bb";
	Singleton<A>::Instance(str);
	Singleton<B>::Instance(std::move(str));
	Singleton<C>::Instance(1,3.14);
	Singleton<C>::GetInstance()->Fun();

	Singleton<A>::DestroyInstance();
	Singleton<B>::DestroyInstance();
	Singleton<C>::DestroyInstance();

	return 0;
}