条款15: 在资源管理类中提供对原始资源的访问

将RAII class对象转换为其所含原始资源，有两个做法：显示转换和隐式转换

 

显示：

std::trl::shared_ptr<Investment>pInv(createInvestment()); int daysHeld(const Investment* pi); int days = daysHeld(pInv);//错误 int days = daysHeld(pInv.get());//正确

隐式：

class Investment{ public: bool isTaxFree() const; ... }; Investment* createInvestment(); std::trl::shared_ptr<Investment> pil(creatInvestment()); bool taxable1 = !(pil->isTaxFreeee());//经由operator->访问资源 ... std::auto_ptr<Investment> pi2(createInvestment()); bool taxable2 = !((*pi2).isTaxFree()); ...

一般而言显式转换比较安全，但隐式转换对客户比较方便