c++ - 与类型同名的类型别名

Question

它是有效的 C++ 吗？

#include <iostream>


class Test {

    struct Inner {
    };

public:
    using Inner = struct Inner;  // Alias with same name as type
};

int main(int argc, const char * argv[]) {
    static_assert(std::is_pod<Test::Inner>::value, "");
    
    return 0;
}

使用 clang 编译但不能使用 GCC/Visual C++ 编译(“Inner is private ...”错误消息)

Answer 1

GCC 和 Visual C++ 是正确的。

确实可以使用 using实际上更改成员的访问权限，例如

using Inner_ = Inner;

和

static_assert(std::is_pod<Test::Inner_>::value, "");

在函数中。

但是在类型别名与成员同名的情况下，C++ 要求范围解析运算符查找成员。所以在你的情况下 Test::Inner指实际成员而不是 using因此编译应该失败，因为它是 private .

见 https://en.cppreference.com/w/cpp/language/qualified_lookup , 特别是

Qualified lookup within the scope of a namespace N first considers all declarations that are located in N and all declarations that are located in the inline namespace members of N (and, transitively, in their inline namespace members). If there are no declarations in that set then it considers declarations in all namespaces named by using-directives found in N and in all transitive inline namespace members of N