为什么我不能放一个“使用"?类声明中的声明? [英] Why can't I put a "using" declaration inside a class declaration?

问题描述

我理解将 using 声明放入头文件时可能会遇到的麻烦，所以我不想这样做.相反，我尝试将 using(或 命名空间 foo =)放在类声明中，以减少头文件中的重复输入.不幸的是，我收到编译器错误.看起来这将是一个有用的功能.

I understand the troubles you can get into when you put a using declaration inside a header file, so I don't want to do that. Instead I tried to put the using (or a namespace foo =) within the class declaration, to cut down on repetitive typing within the header file. Unfortunately I get compiler errors. Seems like it would be a useful feature.

#ifndef FOO_H
#define FOO_H

// This include defines types in namespace gee::whiz::abc::def,
// such as the class Hello.
#include "file_from_another_namespace.h"

// using namespace gee::whiz::abc::def; // BAD!

namespace x {
   namespace y {
      namespace z {

struct Foo {
    using namespace gee::whiz::abc::def; // Illegal.
    namespace other = gee::whiz::abc::def; // Illegal.

    // Foo(gee::whiz::abc::def::Hello &hello); // annoyingly long-winded

    Foo(other::Hello &hello); // better
    //...
};

} } } // end x::y::z namespace

#endif // FOO_H

在实际代码中，命名空间名称要长得多且烦人，而且我无法更改.

In the real code, the namespace names are much longer and annoying and it's not something I can change.

谁能解释为什么这不合法，或者(更好)是否有解决方法?

Can anyone explain why this is not legal, or (better) if there's a workaround?

推荐答案

你能做 typedef gee::whiz::abc::def::Hello Hello 吗?

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