Ref-qualified成员函数的目的是什么？ [英] What is the purpose of Ref-qualified member functions ?

问题描述

在阅读 http://en.cppreference.com/w/cpp/language/ member_functions ，我遇到了一些事情，我以前没有见过： lvalue / rvalue Ref-qualified member functions 。他们的目的是什么？

While reading http://en.cppreference.com/w/cpp/language/member_functions, I came across something, I haven't seen before: lvalue/rvalue Ref-qualified member functions. What would be their purpose ?

推荐答案

请在下面阅读：

在重载解析期间，类X的非静态cv限定成员函数被视为一个函数，如果没有参照限定符，则采用类型为lvalue的隐式参数引用cv限定的X;如果它有lvalue ref-qualifier。否则（如果它有rvalue ref-qualifier），它被视为一个函数，它采用类型为rvalue的隐式参数引用cv限定的X.

During overload resolution, non-static cv-qualified member function of class X is treated as a function that takes an implicit parameter of type lvalue reference to cv-qualified X if it has no ref-qualifiers or if it has the lvalue ref-qualifier. Otherwise (if it has rvalue ref-qualifier), it is treated as a function taking an implicit parameter of type rvalue reference to cv-qualified X.

示例

Example

#include <iostream>
struct S {
    void f() & { std::cout << "lvalue\n"; }
    void f() &&{ std::cout << "rvalue\n"; }
};

int main(){
    S s;
    s.f();            // prints "lvalue"
    std::move(s).f(); // prints "rvalue"
    S().f();          // prints "rvalue"
}

因此在重载解析过程中，编译器会查找函数& -qualified如果调用对象是 lvalue 或对于函数& -qualified如果调用对象是右值。

So during overload resolution the compiler looks for the function &-qualified if the caller object is an lvalue or for the function &&-qualified if the caller object is an rvalue.

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