CODEWITHSUNDEEP
c++namespaces
Roman L
Roman L

Reputation: 3056

How to properly use namespaces to avoid name collision?

I'm a bit confused concerning proper usage of C++ namespaces. It is clear for me how they can help to avoid conflicts (name collision), but it is not clear anymore when it comes to the using keyword. I mean, suppose I have a part of my code that I put into a namespace, and create a class, say

namespace my
{
    class vector { ... };
}

Of course, when I use it, I wouldn't like to type my::vector all the time, so I'd like using namespace my. However, I could eventually need something from the std namespace, and then I want using namespace std at the same time, but this will bring me back to the initial name collision problem.

I know that it is possible to "import" only the functionality that I need, like using std::set, but in this case it seems natural to import both the standard namespace std and my namespace completely as I'd use both of them all the time.

Does this mean that even when I use namespaces I should still think about giving non-common names to my types? Or is using namespace a mistake and I should always type my::vector instead? Thanks.

Well, I should probably clarify that it is more a question of readability than typing. Lots of :: everywhere look really weird to me. I know it's a question of taste and habits, but nevertheless.

Upvotes: 5

Views: 3810

Answers (3)

Bo Persson
Bo Persson

Reputation: 92261

Why bother putting it in a namespace in the first place, if you are immediately opening up the namespace again? You could just as well have put the class in the global namespace!

It would also be very confusing for people who didn't notice the using directive at the top of your file, that vector isn't std::vector. That in itself is a reason for writing my::vector!

To me, seeing names like std::vector and std::list actually improves readability, because I immediately know what those names mean.

Upvotes: 1

André Caron
André Caron

Reputation: 45224

Of course, when I use it, I wouldn't like to type my::vector all the time, so I'd like using namespace my. However, I could eventually need something from the std namespace, and then I want using namespace std at the same time, but this will bring me back to the initial name collision problem.

Yes, it would bring you back to the initial name collision problem. This is why you should use using namespace ...; directives sparingly, and only in source files, never in headers.

Does this mean that even when I use namespaces I should still think about giving non-common names to my types?

No, you shouldn't. Namespaces were invented precisely to avoid this.

Or is using namespace a mistake and I should always type my::vector instead?

You can, if you want to, use the using namespace ...; or using ...; directives until you get conflicts. This means that when you do have conflicts, you'll end up writing "unnatural" code by explicitly quallifying names in some places.

In practice, when you're dealing with short namespace names (i.e. std), you can just type them explicitly all the time. After a week or so, you won't even notice you're typing it anymore.

Upvotes: 10

Fred Foo
Fred Foo

Reputation: 363567

If your code uses both std::vector and my::vector, then always writing the names in full is the best option.

Upvotes: 4

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