I just finished watching an episode of Bob Martin at NDC where he said "using" directives in C# at the top of a page are bad because of the tight coupling they create/imply between components.
What way are there to use external .dlls without adding a project reference and a using statement?
I remember V6 used to let you create an object by the string of the ProgId--I'm not sure that's the technique I'm looking for, but it's an example of a language that didn't need a project reference to use a dll.
EDIT: Here is a link to the conference. Sorry I don't have the exact quote or minute in the presenation, I'm going by memory.
It's not the using statement itself that is bad - it's if you get too many of them.
A statement such as using System; is rarely a problem in itself, but if you have lots (I'd say more than 3-6, depending on which ones) in the same code file, it could be an indication of tight coupling.
You could just as well apply a similar rule of thumb to the number of references in a project itself.
The solution to tight coupling is programming to interfaces and Dependency Injection (DI).
The ProgId way of doing things that you can remember from VB was simply COM in action. In essence, you used that ProgId to get a reference to an instance that implemented the desired interface. The downside was that this only worked when the COM object was universally registered. Remember dll hell?
You can still apply the same principle using certain flavors of DI, only that now the interface is a .NET type and not defined in IDL, and you need some sort of DI Container to supply the concrete implementation.