template <typename T>
class SmartPtr {
private:
    T *ptr_;
    size_t *count_;

public:
    explicit SmartPtr(T *p = nullptr): ptr_(p), count_(new size_t){
        if(p)
            *count_ = 1;// count_ = new size_t(1)
        else
            *count_ = 0;
    }

    SmartPtr(const SmartPtr& smart_ptr){
        if(this != smart_ptr){  // 避免自赋值
        ptr_ = smart_ptr.ptr_;
        count_ = smart_ptr.count_;
        (*count_)++;        
        }
    }

    ~SmartPtr(){
        if(--(*count_) == 0){
            delete ptr_;
            delete count_;
        }
    }

    SmartPtr& operate=(SmartPtr& smart_ptr){
        if(this->ptr_ != smart_ptr.ptr_){
            // 原来的指向 -1
            if(this->ptr_){
                if(--(*count_) == 0){
                    delete ptr_;
                    delete count_;
                }
            }
            this->ptr_ = smart_ptr.ptr_;
            this->count_ = smart_ptr.count_;
            (*this->count_)++;
            // 新指向的this +1
        }
        return *this;
    }

    T* operator->(){
        assert(this->ptr_ == nullptr);
        return *ptr_;
    }
    T& operate*(){
        if(ptr_)
            return ptr_;
    }
}