?????e?????reference???????????????????????????line4???÷???
?????????????????????????????r ??????line4 ????? r ?????? 3 ??????????? alias ?????????????????
?????????????????????????r ??????????????? x ???????????????У??? r ?? alias ?????????????????????????????
??????????????reference ?????????“??????????”?????? ??????“pointer-alias” ?????????????-?÷?-???????????????????? reference ?????С?
??????????ж?????????OOP ??C++ ???OOP????????????????? polymorphism?? ????????“????”???????????????“????”??????????derived  class?????????????A???????B??????A??B??????????????????????????????? polymorphic ???????????????? reference??????????“??????”???????????? reference ?????????????polymorphic variable?? ????????????????????в??????“????”????????????′???????
???????polymorphic variable?????????reference???????????????????????????????????????????????????????C++ ??object model?????????? - ????????????????????????????????C++?????????????????????????????????C++??????????
????????????reference ?????????????????????????????????????λ??壺
????Alias (???????)
????Pointer ?????
????Polymorphic variable ??????????????????????????????????????????????????????????????????????????“??”?????????
??????????????????????????????ū?????????????????????????C++???Щ?????????????????????????C++??????????
???????????????
????1??C++???Щ???????????????????????????????????????д?“????”???????????????“????”???????????????????????
????2??C++????????????????????????C++???????????????????Java??C#?? JavaScript????????????????????????????“????”??95%????????
????3??????C++??????C++???????????????д?????????????????C++?????????????????????