Redundant code

[Doug Crowley]

I often have different classes in a project whose methods rely on standard
routines. For example, I'm working on a project now that has two classes which
uses bitwise operations that are contained in a module called modBitWise.bas.

One of these classes is project specific while the other could be used in future
projects. Do you consider it prudent to duplicate this code in the reusable
class so that it can be standalone? Otherwise I'll have to make sure that I
include modBitWise.bas in any project that reuses this class.

[Tim Patrick]

One of the main purposes of a class is to hide the details of functionality
behind a set of defined interfaces (much like an ActiveX object's purpose).
The class is like a black box; the consumer of a class shouldn't be bothered
by the insides of the box, including any dependencies required by the box.

While this is a great goal, it can lead to some inefficiency, such as the
duplicate code issue you mention here. You can call global functions from
inside a class. In fact, the presence of the Friend keyword almost begs
the programmer to have classes interact with each other.

You could place the bitwise functions in a DLL of their own, and make that
DLL a dependency of each of the two classes. In that way, it could continue
to be a dependency for the class that will go on to future projects. Still,
that seems like overkill for the type of work you are describing.

If I was in your place, I would probably duplicate the code in the module
that you plan to use in other projects. It would be hard, and my hands would
shake with each copy and paste of the code. But this would have the benefit
of giving the class that true black-box feeling. And, isn't that was every
class really desires, deep down in its heart? :-)

-----
Tim Patrick
tim@vbstyleguide.com