Question

I’ve a class and an enum value which have the same name. Inside the class I want to use the enum which gives an error. Is there any way to use the enum without renaming or moving to a different namespace?

Example:

namespace foo {
    enum bar {
        BAD
    };

    class BAD {
        void worse () {
            bar b = BAD; // error
        }
    };
};

Answer 1

This is one of those tricky parts of how the name lookup is performed.

There are two identifier scopes in C++, one for class types and general identifier scope. The enum value BAD resides in the general identifier scope, while the class type BAR resides in the class identifier scope. That is the reason why you are allowed to have both an enum value and a class with the same name: both names do not collide.

Within class BAD, the identifier lookup rules will find the class BAD before it finds the enum, and thus the error. Now, if you fully qualify the identifier then the name lookup will first check the global identifier scope and match the enum value. On the opposite end, you will have to add the struct or class keyword to declare variables of type BAD.

namespace foo {
   enum bad { BAD; };
   class BAD {
      void worse() { bad b = ::foo::BAD; } // fully qualified will match the enum
   };
}
int main() {
   // foo::BAD b;    // error, foo::BAD is an enum, not a type
   class foo::BAD b; // correct
}

Now, I would advice against this usage. It is generally not a good idea to reuse an identifier like this. Code will be more complex, and probably misleading for the casual reader (the same unqualified identifier refers to different things when used in different contexts). If the names do need to be BAD, consider using an enclosing namespace or class for either the class or the enum (prefer the enum there).