Any valid reason for code duplication? [closed]

Answer 1

Laziness, that's the only reason I can think of.

On a more serious note. The only valid reason I can think of is changes at the very end of the product cycle. These tend to undergo a lot more scrutiny and the smallest change tends to have the highest rate of success. In that limited circumstance it is easier to get a code duplication change through as opposed to refactoring out a smaller change.

Still leaves a bad taste in my mouth.

Answer 2

A good read about this is large scale c++ software design by John Lakos.

He has many good points about code duplication, where it might help or hinder a project.

The most important point is asking when deciding to remove duplication or duplicate code:

If this method changes in the future, do I want to change the behaviour in the duplicated method, or needs it to stay the way it is?

After all, methods contain (business) logic, and sometimes you'll want to change the logic for every caller, sometimes not. Depends on the circumstances.

In the end, it's all about maintenance, not about pretty source.

Answer 3

Since there is the "Strategy Pattern", there is no valid reason for duplicate code. Not a single line of code must be duplicated, everything else is epic fail.

Answer 4

A long time ago when I used to do graphics programming you would, in some special cases, use duplicate code this way to avoid the low level JMP statements generated in the code (it would improve performance by avoiding the jump to the label/function). It was a way to optimize and do a pseudo "inlining".

However, in this case, I don't think that's why they were doing it, heh.

Answer 5

Besides being inexperienced, there is why duplicated code occurrences might show up:

No time to properly refactor

Most of us are working in a real world where real constraints force us to move quickly to real problems instead of thinking about niceness of the code. So we copy&paste and move on. With me, if I later see that code is duplicated several more times, it is the sign that I have to spend some more time on it and converge all instances to one.

Generalization of the code not possible/not 'pretty' due to language constraints

Lets say that deep inside a function you have several statements that greatly differ from instance to instance of same duplicated code. For example: I have a function that draws 2d array of thumbnails for the video, and it's embedded with calculation of each thumbnail position. In order to calculate hit-test (calculate thumbnail index from click position) I am using same code but without painting.

You are not sure that there will be generalization at all

Duplicate code at first, and later observe how it will evolve. Since we are writing software, we can allow 'as late as possible' modifications to the software, since everything is 'soft' and changeable.

I'll add more if I remember something else.

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Added later...

Loop unrolling

In time before compilers were smart as Einstein and Hawking combined, you had to unroll the loops or inline code to be faster. Loop unrolling will make your code to be duplicated, and probably faster by few percents, it compiler didn't do it for you anyway.

Answer 6

The only "valid" thing I can see this arising from is when those lines of code were different, then converged to the same thing through subsequent edits. I've had this happen to me before, but none too frequently.

This is, of course, when it's time to factor out this common segment of code into new functionality.

That said, I can't think of any reasonable way to justify duplicate code. Look at why it's bad.

It's bad because a change in one place requires a change in multiple places. This is increased time, with a chance of bugs. By factoring it out, you maintain the code in a single, working location. After all, when you write a program you don't write it twice, why would a function be any different?