使用"using"指令隐藏名称 [英] Hiding names with 'using' directive

问题描述

代码示例:

struct A {};
struct B { using A = A; };

int main()
{
    B b;
}

Clang编译它.但是GCC给出了以下错误(演示):

Clang compiles it. But GCC gives the following error (demo):

声明使用A =结构A"会更改"A"的含义

declaration of 'using A = struct A' changes meaning of 'A'

C ++标准说:

如果在同一声明性区域(以任何顺序)中声明了类名([class.name])或枚举名([dcl.enum])以及变量，数据成员，函数或枚举器具有相同的名称(不包括通过使用指令可见的声明([basic.lookup.unqual]))，无论变量，数据成员，函数或枚举器名称在何处，类或枚举名称均隐藏可见.

If a class name ([class.name]) or enumeration name ([dcl.enum]) and a variable, data member, function, or enumerator are declared in the same declarative region (in any order) with the same name (excluding declarations made visible via using-directives ([basic.lookup.unqual])), the class or enumeration name is hidden wherever the variable, data member, function, or enumerator name is visible.

UPD.0 :感谢莫斯科的弗拉德

UPD.0: thanks to Vlad from Moscow

在S类中使用的名称N在上下文中以及在S的完整范围中进行重新评估时应引用同一声明.对于此规则的违反，无需进行诊断

A name N used in a class S shall refer to the same declaration in its context and when re-evaluated in the completed scope of S. No diagnostic is required for a violation of this rule

这是否意味着GCC行为不正确?谢谢！

Does that mean that GCC behavior is incorrect? Thanks!

推荐答案

似乎是gcc的错误.根据C ++ 20标准(6.3.7类范围)

It seems that it is a bug of gcc. According to the C++ 20 Standard (6.3.7 Class scope)

2在S类中使用的名称N应指代与它的上下文以及在S的完整范围中进行重新评估时.违反此规则需要进行诊断.

2 A name N used in a class S shall refer to the same declaration in its context and when re-evaluated in the completed scope of S. No diagnostic is required for a violation of this rule.

在这种情况下

struct A {};
struct B { using A = A; };

名称 B :: A 表示与 struct A 相同的声明.

the name B::A refers to the same declaration of struct A.

这是C ++标准中的一个示例，它显示了引号的含义.

Here is an example from the C++ Standard that shows the meaning of the quote.

typedef char* T;
struct Y {
   T a; // error: T refers to ::T but when reevaluated is Y::T
   typedef long T;
   T b;
};

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