c++ - 同名的 typedef 和模板参数

Question

为什么这种情况不正确(这是合乎逻辑的)

template <typename T>
struct Der: public Base
{
    typedef int T;
    T val;
};

，但这种情况是正确的吗？

struct Base
{
    typedef int T;
};

template <typename T>
struct Der: public Base
{
    T val;
};

标准 14.6.1/7 说:

In the definition of a class template or in the definition of a member of such a template that appears outside of the template definition, for each base class which does not depend on a template-parameter (14.6.2), if the name of the base class or the name of a member of the base class is the same as the name of a template-parameter, the base class name or member name hides the template-parameter name (3.3.7).

为什么这里没有歧义？

Answer 1

根据 [temp.local]/6，第一个例子是不正确的:

A template-parameter shall not be redeclared within its scope (including nested scopes).

然而，在

template <typename T>
struct Der: public Base
{
    T val;
};

T 被继承自 Base 的名称隐藏 - 正如您的引用所指定的那样。

[..] if the name of the base class or the name of a member of the base class is the same as the name of a template-parameter, the base class name or member name hides the template-parameter name (3.3.7).

也就是说，成员val的类型是int。 Demo .