template<class T>
class SharedPointer
{
public:
    //默认构造函数，内部指针，未指向任何资源，引用计数为0,因为它未与任何资源绑定
    SharedPointer() :m_refCount(nullptr), m_pointer(nullptr){}

    //构造函数，初始化时，指向一个已经分配好的资源
    SharedPointer(T* adoptTarget) :m_refCount(nullptr), m_pointer(adoptTarget)
    {
        addReference();
    }

    //构造函数，使用其它对象创建新对象
    SharedPointer(const SharedPointer<T>& copy)
        :m_refCount(copy.m_refCount), m_pointer(copy.m_pointer)
    {
        addReference();
    }

    //析构函数，引用计数递减，当为0时，释放资源
    virtual ~SharedPointer()
    {
        removeReference();
    }

    //赋值操作
    //当左值被赋值时，表明它不再指向所指的资源，故引用计数减一
    //之后，它指向了新的资源，所以对应这个资源的引用计数加一
    SharedPointer<T>& operator=(const SharedPointer<T>& that)
    {
        if (this != &that)
        {
            removeReference();
            this->m_pointer = that.m_pointer;
            this->m_refCount = that.m_refCount;
            addReference();
        }
        return *this;
    }

    //判断是否指向同一个资源
    bool operator==(const SharedPointer<T>& other)
    {
        return m_pointer == other.m_pointer;
    }
    bool operator!=(const SharedPointer<T>& other)
    {
        return !operator==(other);
    }

    //指针解引用
    T& operator*() const
    {
        return *m_pointer;
    }
    //调用所知对象的公共成员
    T* operator->() const
    {
        return m_pointer;
    }

    //获取引用计数个数
    int GetReferenceCount() const
    {
        if (m_refCount)
        {
            return *m_refCount;
        } 
        else
        {
            return -1;
        }
    }

protected:
    //当为nullpter时，创建引用计数资源，并初始化为1
    //否则，引用计数加1。
    void addReference()
    {
        if (m_refCount)
        {
            (*m_refCount)++;
        }
        else
        {
            m_refCount = new int(0);
            *m_refCount = 1;
        }
    }

    //引用计数减一，当变为0时，释放所有资源
    void removeReference()
    {
        if (m_refCount)
        {
            (*m_refCount)--;
            if (*m_refCount == 0)
            {
                delete m_refCount;
                delete m_pointer;
                m_refCount = 0;
                m_pointer = 0;
            }
        }
    }

private:
    int * m_refCount;
    T   * m_pointer;
};