April 2018
Intermediate to advanced
303 pages
4h 54m
Chinese
Content preview from Effective Modern C++（中文版）
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.
192
｜
第
5
章
果在
typedef
的创建或者评估求值的过程中出现了引用的引用，引用折叠就会出手消
灭之。例如，假设我们有个类模板
Widget
，内嵌一个右值引用型别的
typedef
，
template<typename T>
class Widget {
public:
typedef T&& RvalueRefToT;
…
};
再假设我们以左值引用型别来实例化该
Widget
：
Widget<
int&
> w;
在
Widget
中以
int&
代入
T
的位置，则得到如下的
typedef
：
typedef
int& &&
RvalueRefToT;
引用折叠又将上述语句化简得到：
typedef
int&
RvalueRefToT;
这个结果显然表明，我们为
typedef
选择的名字也许有些名不符实：当以左值引用型
别实例化
Widget
时，
RvalueRefToT
其实成了个左值引用的
typedef
。
最后一种会发生引用折叠的语境在于
decltype
的运用中。如果在分析一个涉及
decltype
的型别过程中出现了引用的引用，则引用折叠亦会介入并消灭之（有关
decltype
的信息，详见条款
3
）。
要点速记
•
引用折叠会在四种语境中发生：模板实例化、
auto
型别生成、创建和运用
typedef
和别名声明，以及
decltype
。
•
当编译器在引用折叠的语境下生成引用的引用时，结果会变成单个引用。
如果原始的引用中有任一引用为左值引用，则结果为左值引用。否则，结
果为右值引用。
•
万能引用就是在型别推导的过程会区别左值和右值，以及会发生引用折叠 ...
Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.