C++ Namespaces & templates question

Question

Hi!

I have some functions that can be grouped together, but don't belong to some object / entity and therefore can't be treated as methods.

So, basically in this situation I would create a new namespace and put the definitions in a header file, the implementation in cpp file. Also (if needed) I would create an anonymous namespace in that cpp file and put all additional functions that don't have to be exposed / included to my namespace's interface there.

See the code below (probably not the best example and could be done better with another program architecture, but I just can't think of a better sample...)

Sample code (header)

namespace algorithm {
   void HandleCollision(Object* object1, Object* object2);
}

Sample code (cpp)

#include "header"

// Anonymous namespace that wraps 
// routines that are used inside 'algorithm' methods
// but don't have to be exposed
namespace {
   void RefractObject(Object* object1) {
      // Do something with that object
      // (...)
   }
}

namespace algorithm {
   void HandleCollision(Object* object1, Object* object2) {
      if (...) RefractObject(object1);
   }
}

So far so good. I guess this is a good way to manage my code, but I don't know what should I do if I have some template-based functions and want to do basically the same.

If I'm using templates, I have to put all my code in the header file. Ok, but how should I conceal some implementation details then?

Like, I want to hide RefractObject function from my interface, but I can't simply remove it's declaration (just because I have all my code in a header file)...

The only approach I came up with was something like:

Sample code (header)

namespace algorithm {
   // Is still exposed as a part of interface!
   namespace impl {
      template <typename T>
      void RefractObject(T* object1) {
         // Do something with that object
         // (...)
      }
   }

   template <typename T, typename Y>
   void HandleCollision(T* object1, Y* object2) {
      impl::RefractObject(object1);
      // Another stuff
   }
}

Any ideas how to make this better in terms of code designing?

Answer 1

That's a pretty common solution. Boost does it, and I do it as well, but with the detail namespace instead. Just make it a rule: "don't look inside detail!"

File-wise, I recommend giving details their own file, and tucking it away in a detail folder. That is, my code would be akin to:

//           v
#include "detail/RefractObject.hpp"

namespace algorithm {

   template <typename T, typename Y>
   void HandleCollision(T* object1, Y* object2) {
      detail::RefractObject(object1);
      // Another stuff
   }
}

This is just good code practice in general (keep things split up and re-usable) and keeps the header file cleaner of implementation details.

Answer 2

You can't hide your source from the user unless you're going to compile it first, which is impossible with templates. So I suggest, in a sense, that you don't bother.

Also gotta ask why Refract can't be a member method.