C++模板实现单例模式

早在第一篇博文中,最后提出一个问题,使用模板来实现单例模式.现给出方法.

singleton.h

#pragma once
#include <memory>
#include <mutex>

template<typename T>
class Singleton {
public:
    static std::shared_ptr<T> instance() {
        std::call_once(_onceFlag,[](){
            _instance = std::shared_ptr<T>(new T());
        });
        return _instance;
    };

protected:
    Singleton() {};
    ~Singleton() {};

private:
    Singleton(const Singleton& other);
    Singleton &operator=(const Singleton& other);

    static std::once_flag _onceFlag;
    static std::shared_ptr<T> _instance;
};

template<typename T>
static std::once_flag Singleton<T>::_onceFlag;

template<typename T>
static std::shared_ptr<T> Singleton<T>::_instance;

sample.h

#pragma once
#include "singleton.h"

class Sample : public Singleton<Sample> {
    friend class Singleton<Sample>;

public:
    ~Sample();
private:
    Sample();
};