April 2018
Intermediate to advanced
303 pages
4h 54m
Chinese
Content preview from Effective Modern C++（中文版）
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28
｜
第
1
章
量声明成了一个
std::initializer_list
，其实本意却并非如此。正是由于这个陷阱
的存在，很多程序员都只在必要的时候才会使用大括号括起的初始化表达式（至于什
么是必要的时候，请参见条款
7
）。
关于
C++11
，上面所说的就是全部了。但是关于
C++14
，还有别的话要说。
C++14
允
许使用
auto
来说明函数返回值需要推导（参见条款
3
），而且
C++14
中的
lambda
式
也会在形参声明中用到
auto
。然而，这些
auto
用法是在使用模板型别推导而非
auto
型别推导。所以，带有
auto
返回值的函数若要返回一个大括号括起的初始化表达式，
是通不过编译的：
auto
createInitList()
{
return
{ 1, 2, 3 }
;
//
错误：无法为
{ 1, 2, 3 }
完成型别推导
}
同样地，用
auto
来指定
C++14
中
lambda
式的形参型别时，也不能使用大括号括起
的初始化表达式：
std::vector<int> v;
…
auto resetV =
[&v](const
auto
& newValue) { v = newValue; };
// C++14
…
resetV(
{ 1, 2, 3 }
);
//
错误
!
无法为
{ 1, 2, 3 }
完成型别推导
要点速记
•
在一般情况下，
auto
型别推导和模板型别推导是一模一样的，但是
auto
型别
推导会假定用大括号括起的初始化表达式代表一个
std::initializer_list
，
但模板型别推导却不会。
•
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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.
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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.