条款15: 在资源管理类中提供对原始资源的访问

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

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());
...