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