为什么编译器支持冗余范围限定，是否合法?
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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