April 2018
Intermediate to advanced
303 pages
4h 54m
Chinese
Content preview from Effective Modern C++（中文版）
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转向现代
C++
｜
101
需要重点提请注意的是，
constexpr
是对象和函数接口的组成部分。
constexpr
实际上
宣告的是：“但凡任何
C++
要求在此使用一个常量表达式的语境，皆可以用我。”一
旦你把一个对象或函数声明成了
constexpr
，客户就可以将其用于这种语境。而万一
你后来又感觉你对
constexpr
的运用不当，然后移除了它，这个动作就可以导致无穷
无尽的客户代码被拒绝编译（仅仅是向函数体里出于调试或性能调优的目的而增添一
条
I/O
语句就可能导致这么个局面，因为通常来说，
constexpr
函数里是不允许有
I/O
语句的）。“只要有可能使用
constexpr
，就使用它”这句话中的“只要有可能”的
含义就是你是否有一个长期的承诺，将由
constexpr
带来的种种限制施加于相关的函
数和对象之上。
要点速记
•
constexpr
对象都具备
const
属性，并由编译期已知的值完成初始化。
•
constexpr
函数在调用时若传入的实参值是编译期已知的，则会产出编译期
结果。
•
比起非
constexpr
对象或
constexpr
函数而言，
constexpr
对象或是
constexpr
函数可以用在一个作用域更广的语境中。
条款
16
：保证
const
成员函数的线程安全性
在数学领域中，使用一个类来表示多项式会非常方便。而在这个类中，若有一个函数
能够计算多项式的根，即那些使得多项式求值结果为零的值，将会很有用。这样一个
函数并不会造成多项式的值的改动，因此将它声明为
const
成员函数也很自然。
class Polynomial ...
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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.