我哪里错了？查找名称 Node 会找到结构 Node 的 injected-class-name

Question

我对 §3.4.4/3 (C++14) 示例中的第一条评论有疑问：

struct Node {
    struct Node* Next; // OK: Refers to Node at global scope
    struct Data* Data; // OK: Declares type Data
                       // at global scope and member Data
};

从 §3.3.2/7（见下文）可以得出结论，该评论是正确的，因为全局名称空间是包含声明 struct Node* Next; 的最小名称空间。

§3.3.2/7（我的重点）

The point of declaration of a class first declared in an elaborated-type-specifier is as follows:

for a declaration of the form

class-key attribute-specifier-seq_opt identifier ;

the identifier is declared to be a class-name in the scope that contains the declaration, otherwise

for an elaborated-type-specifier of the form

class-key identifier

if the elaborated-type-specifier is used in the decl-specifier-seq or parameter-declaration-clause of a function defined in namespace scope, the identifier is declared as a class-name in the namespace that contains the declaration; otherwise, except as a friend declaration, the identifier is declared in the smallest namespace or block scope that contains the declaration. [ Note: These rules also apply within templates. —end note ] [ Note: Other forms of elaborated-type-specifier do not declare a new name, and therefore must refer to an existing type-name. See 3.4.4 and 7.1.6.3. —end note ]

但是从 §3.4.4/2（见下文）我得到的印象是查找名称 Node 找到注入的-class-名称 Node，所以它不能在全局范围内引用 Node。

§3.4.4/2（我的重点）

If the elaborated-type-specifier has no nested-name-specifier, and unless the elaborated-type-specifier appears in a declaration with the following form:

class-key attribute-specifier-seq_opt identifier ;

the identifier is looked up according to 3.4.1 but ignoring any non-type names that have been declared. If the elaborated-type-specifier is introduced by the enum keyword and this lookup does not find a previously declared type-name, the elaborated-type-specifier is ill-formed. If the elaborated-type-specifier is introduced by the class-key and this lookup does not find a previously declared type-name, or if the elaborated-type-specifier appears in a declaration with the form:

class-key attribute-specifier-seq_opt identifier ;

the elaborated-type-specifier is a declaration that introduces the class-name as described in 3.3.2.

Answer 1

3.3.2 中的段落是关于声明 classes，而不是对象。

您的声明 struct Node* Next 不可能匹配“class-key identifier”；后者只匹配前者中一半的标记。

Answer 2

[basic.scope.pdecl]/7 的第一句清楚地表明该段涉及 a class 首先在 elaborated-type-specifier 中声明；因此它不适用于 struct Node* Next; 中的 struct Node，因为 Node 不是首先在 elaborated-type-specifier.[=16 中声明的=]

相反，Node 的非限定名称查找确实找到了 injected-class-name（参见 [basic.lookup.unqual]/p1和 7.1) 而不是 ::Node。不过，您需要为此编写一些相当人为的代码。例如：

struct A {};
struct B : private A {};
struct C : public B {
    struct A m_a; // error: A is the inaccessible injected-class-name, not ::A
    struct ::A m_a2; // OK
};

请注意，GCC 接受此代码，我认为这是一个错误。

我哪里错了？查找名称 Node 会找到结构 Node 的 injected-class-name

Where am I wrong here? The lookup for the name Node finds the injected-class-name for the struct Node

c++

lookup

language-lawyer

c++14