A note: I originally composed this blog post in June 2008, but lost it in my backlog and it never got posted. In the interim, Robert C. "Uncle Bob" Martin has addressed the issue in his Clean Code Tip of the Week #1. He describes the issue and the dilemma far more concisely than I have here, and even provides a strategy for dealing with it. By all means feel free to skip my post here and consider him the "official source" on this topic. =)
I am a big fan of "lazy programming". By that of course I mean avoiding repetition and tedium wherever possible. I mean, that's what most programming is really about, right? You have a problem: some process that is annoying, unwieldly, or even impossible to perform with existing tools. And the solution is to write a program that takes care of all the undesirable parts of that process automatically, based on a minimized set of user input or configuration data.
The realities of programming on an actual computer rather than in an idealized theoretical environment rarely allow this ascending staircase of productivity to be climbed to the top step. But it is nevertheless a goal we should always strive for.
Hence Jeff Atwood's recent post about eliminating redundancies.
Anything that removes redundancy from our code should be aggressively pursuedAn honorable goal, to be sure. But no rule is without exception, right?
I humbly submit to you the concept of "incidental redundancy". Incidental redundancy is a repetition of code syntax or semantics that tempts the programmer to refactor, but if carried out the refactoring could damage the elegance and discoverability of the program.
The difference between incidental redundancy and regular redundancy in code is that the redundancy does not arise because of any substantive, or at least relevant, similarity between the two problems in question. Here are two ways I can think of off the top of my head for this to happen:
- The solutions you have come up with to this point for each situation just happen to have taken a similar form. Given a different creative whim, or even just an alternative refactoring, the commonality may never have arisen.
- The problems are, in fact, similar at some level. But the level at which they are similar is far above or below the level where you are working, and so not truly relevant or helpful to the immediate problems you are trying to solve.
The second situation may sound a little incredible. But allow me to point out an example from the world of physics. Please bear with me as this is an area of personal interest, and it really is the best example that comes to mind.
There are four forces in the known universe which govern all interactions of matter and energy, at least one of which I'm sure you've heard of: the electromagnetic, weak nuclear, strong nuclear, and gravitational forces. It is known now that the first two of those apparently very different forces are in fact two different aspects of the same phenomenon (the electroweak force), which only show up as different when ambient temperature is comparatively low. Most physicists are pretty sure that the third force is yet another aspect of that same phenomenon that splits off only at even higher temperatures. And it is suspected that gravity can be unified with the rest at temperatures higher still.
The point of all this is that there are four different phenomena which in fact bear undeniable similarities in certain respects, and these similarities continue to drive scientists to create a generalized theory that can explain it all. But no one in his right mind would try to design, for example, a complex electrical circuit based entirely on the generalized theory of the electroweak force.
The analogy to programming is that, were we to try to shift up to that higher level and formulate an abstraction to remove the redundancy, the effect on the problem at hand would be to make the solution unwieldly, or opaque, or verbose, or any number of other undesirable code smells. All at the cost of removing a little redundancy.
What we have in both physics and in our programming dilemma, is noise. We are straining our eyes in the dark to find patterns in the problem space, and our mind tells us we see shapes. For the moment they appear clear and inevitable, but in the fullness of time they will prove to have been illusions. But making things worse, the shadow you think you see may really exist, it's just not what you thought it was. That's the insidious nature of this noise: what you see may in fact be truth in a grander context. But in our immediate situation, it is irrelevant and problematic.
This concept is admittedly inspired heavily, though indirectly, by Raganwald's concept of "incidental complexity", where a solution takes a cumbersome form because of the act of projecting it upon the surface of a particular programming language, not unlike the way the picture from a digital projector becomes deformed if you point it at the corner of a room.
The real and serious implication of this is that, to put it in Raganwald's terms, if you refactor an incidental redundancy, the message your solution ends up sending to other programmers, and to yourself in the future, ceases to be useful in understanding the problem that is being solved. It starts sending a signal that there is a real and important correlation between the two things that you've just bound up in one generalization. When in fact, it's just chance. And so when people start to build on top of that generalization with those not quite correct assumptions, unnecessary complexities can quite easily creep in. And of course that inevitably impacts maintenance and further development.
Noise is ever-present in the world of programming, as in other creative and engineering disciplines. But it doesn't just come from the intrusive environment of our programming language or our tools as Raganwald pointed out. It can come from our own past experience, and even come from the problem itself.
So be wary. Don't submit unwittingly to the siren song of one more redundancy elimination. Think critically before you click that "refactor" button. Because eliminating an incidental redundancy is like buying those "as seen on tv" doodads to make your life "easier" in some way that was somehow never an issue before. You think it's going to streamline some portion of your life, like roasting garlic or cooking pastries. But in your quest to squeeze a few more drops of efficiency out of the tiny percentage of your time that you spend in these activities, you end up out some cash, and the proud owner of a toaster oven that won't cook anything flat, or yet another muffin pan, and a bunch of common cooking equipment that you probably already own.
So remember, redundancy should always be eliminated, except when it shouldn't. And when it shouldn't is when it is just noise bubbling up from your own mind, or from the problem space itself.