使用指令的歧义名称查找 [英] Ambiguous name lookup with using-directive

问题描述

不允许将名称空间和具有相同名称的类放入一个声明性区域，即

It's not allowed to put a namespace and a class with the same name into one declarative region, i.e.

namespace A {}
class A{};

格式错误(请参见第3.3.1/4节).但是，可以通过using-directive引入任何一个的名称:

is ill-formed (see §3.3.1/4). However, one can introduce the name of either one via a using-directive:

namespace N { namespace A {int i;} }

struct A {static int i;};

using namespace N;

int i = A::i; // The global struct, or namespace N::A?

此代码格式错误吗? VC ++ 如此 以及

Is this code ill-formed? VC++ thinks so, as well as Clang:

main.cpp:7:9: error: reference to 'A' is ambiguous
int i = A::i;
        ^
main.cpp:3:8: note: candidate found by name lookup is 'A'
struct A {static int i;};
       ^
main.cpp:1:25: note: candidate found by name lookup is 'N::A'
namespace N { namespace A {int i;} }
                        ^

但是， GCC接受 .

谁是对的?

推荐答案

代码格式错误.查找A时，第7.3.4/6节进入:

The code is ill-formed. When looking up A, §7.3.4/6 steps in:

如果名称查找在两个不同的名称中找到了一个名称声明 命名空间，并且声明不声明相同的实体，而是 没有声明函数，名称的使用是错误的.

If name lookup finds a declaration for a name in two different namespaces, and the declarations do not declare the same entity and do not declare functions, the use of the name is ill-formed.

这里，名称空间是全局名称空间和N，而实体是名称空间N::A和类::A.

Here, the namespaces are the global namespace and N, and the entities are the namespace N::A and the class ::A.

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