常数& ，&和&& C ++中成员函数的说明符 [英] const& , & and && specifiers for member functions in C++

问题描述

最近我在阅读 API boost :: optional ，并遇到了以下几行：

Recently I was reading through the API of boost::optional and came across the lines:

T const& operator *() const& ;
T&       operator *() & ;
T&&      operator *() && ;

我也写了我自己的程序定义成员函数const&和&& （注意，我不是说的返回类型，而是分号之前的分号），他们似乎工作正常。

I also wrote my own program that defines member functions as const&, & and && (Note that I am not speaking about the return type, but the specifiers just before the semi-colons) and they seems to work fine.

我知道声明一个成员函数const的意思，但是任何人都可以解释它声明它的意义const&和&&< / p>

I know what it means to declare a member function const, but can anyone explain what it means to declare it const&, & and &&.

推荐答案

const& 重载将仅用于const，非const和rvalue对象。

const& means, that this overload will be used only for const, non-const and rvalue object.

const A a = A();
*a;

& 只能用于非const对象。

& means, that this overload will be used only for non-const object.

A a;
*a;

&&& 重载将仅用于右值对象。

&& means, that this overload will be used only for rvalue object.

*A();

有关C ++ 11标准的此功能的更多信息，您可以阅读此帖this的右值引用

for more information about this feature of C++11 standard you can read this post What is "rvalue reference for *this"?

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