Why can't I put a "using" declaration inside a class declaration?

user_95559 0
Viewed 9702

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?

compiler-errors using header namespaces c++
3 Answers

Could you do typedef gee::whiz::abc::def::Hello Hello?

user_1498130

actually not a totally horrid idea. It makes at least as much sense as how it works now (which granted, isn't much). I think the basic problem is that classes are not the unit of compilation and linking, but 'translation units'. But doing it class by class is much cleaner, having classes be modules, like in Java or C# or other languages that make more sense.

user_2047390
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