为什么编译器支持冗余范围限定，是否合法?

Why are redundant scope qualifications supported by the compiler, and is it legal?(为什么编译器支持冗余范围限定，是否合法?)

问题描述

我在两个编译器上进行了测试，很惊讶地发现它们都支持以下定义而毫无怨言:

I tested on two compilers, and was surprised to see both support the following definition without complaint:

class A {
  A();
};

A::A::A() {}
   ^^^

请注意，这也适用于方法，尽管在声明过度限定时会被标记.

Note that this also succeeds for methods, although it is flagged when the declaration is over-qualified.

问题:

• 这是一个有效的 C++ 程序吗?
• 如果是这样，它有什么用途 - 还是仅仅是副产品?

更新详情:

如果最初的问题不清楚或太短:我很好奇为什么在定义中允许使用多余的资格(重点也在上面添加).

In case the original question was not clear or too short: I'm curious why redundant qualifications are permitted on the definition (emphasis also added above).

Clang 和 Apple 的 GCC 4.2 + LLVM 是编译器

推荐答案

Yes, it's allowed (§9/2):

Yes, it's allowed (§9/2):

class-name 也插入到类本身的作用域中；这被称为注入类名.出于访问检查的目的，注入的类名被视为公共成员名.

The class-name is also inserted into the scope of the class itself; this is known as the injected-class-name. For purposes of access checking, the injected-class-name is treated as if it were a public member name.

有关导致类名注入的推理的信息，您可能需要阅读N0444.

For information about the reasoning that lead to class name inject, you might want to read N0444.

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