Any valid reason for code duplication? [closed]

Question

I'm currently reviewing a very old C++ project and see lots of code duplication there.

For example, there is a class with 5 MFC message handlers each holding 10 identical lines of code. Or there is a 5-line snippet for a very specific string transformation every here and there. Reducing code duplication is not a problem in these cases at all.

But I have a strange feeling that I might be misunderstanding something and that there was originally a reason for this duplication.

What could be a valid reason for duplicating code?

Answer 1

I have no problems with duplicated code when it is produced by a source code generator.

Answer 2

When I first started programming, I wrote an app where I had a bunch of similar functionality which I wrapped up in a neat little 20-30 line function ... I was very proud of myself for writing such an elegant piece of code.

Shortly after, the client changed the process in very specific cases, then again, then again, then again , and again, and again .... (many many more times) My elegant code turned into a very difficult, hackish, buggy, & high maintenance mess.

A year later, when I was asked to do something very similar, I deliberately decided to ignore DRY. I put together the basic process, and generated all duplicate code. The duplicate code was documented and I saved the template used to generate the code. When the client asked for specific conditional change (like, if x == y^z + b then 1+2 == 3.42) it was a piece of cake. It was unbelievably easy to maintain & change.

In retrospect, I probably could have solved many of these problems with function pointers and predicates, but using the knowledge I had at the time, I still believe in this specific case, this was the best decision.