Best practices: using namespace or reopen namespace? [closed]

Answer 1

Even though using namespace is the laziest (and therefore the most tempting) solution, it's often not a good idea. Besides what Luchian says about function declarations being ambiguous (someone new to the project wouldn't know if that is standalone function or one in the namespace), and the fact that you might introduce a name in the namespace later, clashing with one you are using now, I have another reason why I'd suggest using the third method.

Using the third method, you give your code more consistency. If A is inside B, you would always define it with A::B. If A is a class and B a function in the class, you would write type A::B(args). If A is a class and B a static member, you would again write type A::B = value. Now A is a namespace, but it's still the same concept: B is defined inside A, therefore it is more consistent to again use A::B.

(There is an added bonus of search-ability if your editor is e.g. ViM)

Answer 2

I think the cleanest way is re-opening the namespace, and I've got the arguments to support it:

• with your second option, with the using directive, it isn't clear that you're implementing a method in that namespace. You could as well be implementing a free function that uses something from the namespace.
• the third option is usually used for implementing class member functions. If you look directly in the cpp file, it isn't clear that you're implementing a function from a namespace unless you know that namespace exists. The first thing that comes to mind is that you're implementing a class member function.
• the first one is the clearest. You open the namespace and define a function inside it. The function is part of the namespace, and this is the implementation.