成员函数上的常量引用限定符 [英] Const reference qualifier on a member function

问题描述

我在那里的答案中看到了:通过右值引用返回是否更有效?

I have seen in an anwser there: Is returning by rvalue reference more efficient?

成员函数定义:

Beta_ab const& getAB() const& { return ab; }

我熟悉成员函数上的 cv-qualifier ( const )，但不熟悉 const& .

I am familiar with the cv-qualifier (const) on member functions, but not const&.

最后一个 const& 是什么意思?

推荐答案

& 是 ref-qualifier .引用限定符是C ++ 11中的新增功能，尚不受所有编译器支持，因此您目前并不经常看到它们.它指定只能在左值(而不是右值)上调用此函数:

The & is a ref-qualifier. Ref-qualifiers are new in C++11 and not yet supported in all compilers, so you don't see them that often currently. It specifies that this function can only be called on lvalues (and not on rvalues):

#include <iostream>

class kitten
{
private:
    int mood = 0;

public:
    void pet() &
    {
        mood += 1;
    }
};

int main()
{
    kitten cat{};
    cat.pet(); // ok

    kitten{}.pet(); // not ok: cannot pet a temporary kitten
}

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结合cv限定符 const ，这意味着您只能在左值上调用此成员函数，而这些值可能是const.

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Combined with the cv-qualifier const, it means that you can only call this member function on lvalues, and those may be const.

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