函数的引用限定符是否有实际用例？ [英] Is there any real use case for function's reference qualifiers?

问题描述

最近我了解了函数的引用限定符，例如

struct foo
{
    void bar() {}
    void bar1() & {}
    void bar2() && {}
};

在我可能需要此功能的地方，该语言功能是否有实际用例？

Where I might need this feature, is there any real use case for this language feature ?

推荐答案

基本上有两种用途：

1. 为了提供优化的重载，例如将成员移出临时对象，而不必复制它。



2. 防止滥用API。例如，没有人会期望

1. To provide an optimized overload, for example to move a member out of a temporary object instead of having to copy it.

2. Prevent misuse of an API. For example, no one would expect

int a = 1 += 2;

正常工作，这也会导致编译错误。但是

to work and this would also cause a compile error. However

string b = string("foo") += "bar";

是合法的

string & operator += (string const & o);

通常是这样。同样，为您的右值提供左值引用也有令人讨厌的副作用。馊主意。可以通过将运算符声明为

as is usually the case. Also this has the nasty side-effect of providing an lvalue-reference to your rvalue. Bad idea. This can easily be prevented by declaring the operator as

string & operator += (string const & o) &;

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