模板的依赖名称解析标准是否存在缺陷
Is it a defect in the standard about dependent name resolution for template
关于如何查找模板的依赖名，标准只给了这么一小句，没有了：
In resolving dependent names, names from the following sources are considered:
- Declarations that are visible at the point of definition of the template.
- Declarations from namespaces associated with the types of the function arguments both from the instantiation context ([temp.point]) and from the definition context.
考虑下面的代码
struct Test{
using type = int;
};
// #1
template<typename T>
struct TMP{
using type = typename T::type;
};
int main(){
TMP<Test>::type v = 0;
}
对于这段代码，名称 type 确实是一个从属名称，因为 T 是一个模板参数，这里不是函数调用，所以，唯一相关的要点是数字 1。它只表示从属name shall be visible before the template definition, 这意味着在我的代码中，声明应该在 #1 处可见。实际上，typename T::type 是一个合格的 id，因此限定名称查找规则适用于它并且因为 T 是一个模板参数，所以查找操作应在给定模板参数之后发生，即在这种模板的特化实例化。但是我引用的引述并没有说明这一点。所以，我想知道这是标准的缺陷吗？如果我遗漏了任何在标准中对此进行解释的内容，请在这个问题中引用它们。
完成language-lawyer comments, in §"Unknown specializations" of this page
Within a template definition, certain names are deduced to belong to
an unknown specialization, in particular,
- a qualified name, if any name that appears to the left of :: is a dependent type that is not a member of the current instantiation
- ...
在你的 struct TMP、
- 类型
T确实是依赖类型
- 表达式
typename T::type是限定名，左边if::是依赖类型
- 该表达式成为未知的专业化
然后说：
Members of unknown specialization are always dependent, and are looked up and bound at the point of instantiation as all dependent names
允许在实例化时查找TMP<Test>::type。
关于如何查找模板的依赖名，标准只给了这么一小句，没有了：
In resolving dependent names, names from the following sources are considered:
- Declarations that are visible at the point of definition of the template.
- Declarations from namespaces associated with the types of the function arguments both from the instantiation context ([temp.point]) and from the definition context.
考虑下面的代码
struct Test{
using type = int;
};
// #1
template<typename T>
struct TMP{
using type = typename T::type;
};
int main(){
TMP<Test>::type v = 0;
}
对于这段代码，名称 type 确实是一个从属名称，因为 T 是一个模板参数，这里不是函数调用，所以，唯一相关的要点是数字 1。它只表示从属name shall be visible before the template definition, 这意味着在我的代码中，声明应该在 #1 处可见。实际上，typename T::type 是一个合格的 id，因此限定名称查找规则适用于它并且因为 T 是一个模板参数，所以查找操作应在给定模板参数之后发生，即在这种模板的特化实例化。但是我引用的引述并没有说明这一点。所以，我想知道这是标准的缺陷吗？如果我遗漏了任何在标准中对此进行解释的内容，请在这个问题中引用它们。
完成language-lawyer comments, in §"Unknown specializations" of this page
Within a template definition, certain names are deduced to belong to an unknown specialization, in particular,
- a qualified name, if any name that appears to the left of :: is a dependent type that is not a member of the current instantiation
- ...
在你的 struct TMP、
- 类型
T确实是依赖类型 - 表达式
typename T::type是限定名，左边if::是依赖类型 - 该表达式成为未知的专业化
然后说：
Members of unknown specialization are always dependent, and are looked up and bound at the point of instantiation as all dependent names
允许在实例化时查找TMP<Test>::type。