Question

I have an enum in a namespace and I’d like to use it as if it were in a different namespace. Intuitively, I figured I could use ‘using’ or ‘typedef’ to accomplish this, but neither actually work. Code snippet to prove it, tested on GCC and Sun CC:

namespace foo
{

enum bar {
    A
};

}

namespace buzz
{
// Which of these two methods I use doesn't matter,
// the results are the same.
using foo::bar;
//typedef foo::bar bar;
}

int main()
{
    foo::bar f; // works
    foo::bar g = foo::A; // works

    buzz::bar x; // works
    //buzz::bar y = buzz::A; // doesn't work
    buzz::bar z = foo::A;
}

The problem is that the enum itself is imported but none of its elements. Unfortunately, I can’t change the original enum to be encased in an extra dummy namespace or class without breaking lots of other existing code. The best solution I can think of is to manually reproduce the enum:

namespace buzz
{
enum bar
{
    A = foo::A
};
}

But it violates the DRY principle. Is there a better way?

Answer 1

Wrap the existing namespace in a nested namespace which you then “use” in the original namespace.

namespace foo
{
    namespace bar_wrapper {
        enum bar {
            A
        };
    }
    using namespace bar_wrapper;
}

namespace buzz
{
    using namespace foo::bar_wrapper;
}