qualified-id 什么意思？

来来，学习英语的时间到了！^_^

欧陆词典

qualified: 有资格的、合格的、胜任的；有限制的、不完全的； modified, limited, or restricted in some way: qualified approval.

词组：well-qualified博览群书的,qualified candidate合格候选人,qualified expression限定表达式,qualified majority特定多数,qualified opinion`附条件意见书、保留意见书；

绝不是zhuangbi，只是先表达在中文翻译没有解答疑惑的时候，就应该捡起英语了。

qualified-id

这里qualified就表示受限的意思，qualified-id自然表示受限制的标识符。那么有没有不受限的呢？非受限标识符2333

这里的受限是指的什么呢？作用域，受作用域或命名空间限制。

如下模式就是qualified-id:[name]::[name::[name::]]id，也就是说标识符的作用域受它们限制的是受限标识符。

unqualified-id自然是光光滑滑的啥也不能有。

nested-name-specifier

qualified-id中name出现了就有nested-name-specifier。

小结

拿stack overflow上的一个回答作为总结¹：

::S is a qualified-id.

In the qualified-id ::S::f, S:: is a nested-name-specifier.

In informal terms1, a nested-name-specifier is the part of the id that

• begins either at the very beginning of a qualified-id or after the initial scope resolution operator (::) if one appears at the very beginning of the id and
• ends with the last scope resolution operator in the qualified-id.

Very informally², an id is either a qualified-id or an unqualified-id. If the id is a qualified-id, it is actually composed of two parts: a nested-name specifier followed by an unqualified-id.

Given:

struct  A {
    struct B {
        void F();
    };
};

• A is an unqualified-id.
• ::A is a qualified-id but has no nested-name-specifier.
• A::B is a qualified-id and A:: is a nested-name-specifier.
• ::A::B is a qualified-id and A:: is a nested-name-specifier.
• A::B::F is a qualified-id and both B:: and A::B:: are nested-name-specifiers.
• ::A::B::F is a qualified-id and both B:: and A::B:: are nested-name-specifiers.

[1] This is quite an inexact description. It's hard to describe a grammar in plain English...

类似的栗子比如：正则化。

References:

1. What is a nested name specifier?