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

```

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

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