C Define function of external namespace inside of nested namespace-CodePudding

Consider the code

namespace A
{    
}

namespace B
{
    namespace ::A
    {
        void func();
    }
}

This is invalid C syntax - but I'm looking for something that works. I need to declare ::A::func(), but from within namespace B (I don't want B::A::func, but A::func).

(If you ask why? then it is because func() will eventually by declared by a macro that also declares some things in namespace B.)

Is is possible?

CodePudding user response：

No it's not possible to somehow reset yourself to the global namespace within the scope of another namespace, for the purpose of declarations.

It could be useful on occasions though and C does pride itself on being a general purpose language, although it would make source code confusing to read as having used namespace ::A you are no longer in namespace B despite the source code telling you otherwise! If you really want to see this then why not propose it to the standards committee?

CodePudding user response：

You can use the using declaration. For example

namespace A
{
    void func();    
}

namespace B
{
    using A::func;
}

Then for example in the global namespace you can write

void other_func()
{
    B::func();
}