Object Mentor Blog: Clean Code and Battle Scarred Architecture

Clean Code and Battle Scarred Architecture

Uncle Bob — Wed, 20 May 2009 17:35:00 -0500

If you go here you’ll see that I struggle to keep the CRAP out of FitNesse. Despite the whimsical name of this metric (which I take a perverse delight in), I find it to be remarkably useful.

CRAP is a metric that is applied to each function in the system. The formula for CRAP is: CRAP = comp(f)^2. X (1 – cov(f)/100)^3. + comp(f)

Where comp(f) = the cyclomatic complexity of the function f. and cov(f) = the unit test coverage of function f.

So a function’s CRAP will be small iff the cyclomatic complexity is low and the test coverage is high. CRAP will be huge if cyclomatic complexity is high, and there is no coverage.

What does this have to do with architecture? Read on…

I work very hard to keep the ratio of crappy methods near .1%. Of the 5643 methods in FitNesse, only 6 are crappy, and five of those I have no control over.

If you study the graph you can see how quickly I react to even the slightest uptick in crap. I don’t tolerate it because it means that either I’ve got a horrifically complex method that needs to be refactored, or (and this is far more likely) I’ve got a method that isn’t sufficiently tested.

Why am I so fastidious about this? Why am I so concerned about keeping the crap out of FitNesse? The reason is pretty simple. It’s the least I can do.

If you look inside of FitNesse, you’ll find that there are lots of structures and decisions that don’t seem to make a lot of sense at first reading. There are complexities and abstractions that will leave you shaking your head.

For example. We generate all our HTML in code. Yes, you read that correctly. We write Java code that constructs HTML. And yes, that means we are slinging angle brackets around.

To be fair, we’ve managed to move most of the angle bracket slingers into a single module that hides the HTML construction behind an abstraction barrier. This helps a lot, but cripe who would sling angle brackets when template system are so prevalent? I hope nobody. But FitNesse was not conceived at a time when template systems made sense (at least to us).

Fear not, I am working through the Fitnesse code replacing the HTML generation with Velocity templates. It’ll take some time, but I’ll get it done. The point is, that just like every other software system you’ve seen, FitNesse is a collection of historical compromises. The architecture shows the scars of many decisions that have since had to be reversed or deeply modified.

What does this have to do with CRAP? Simply this. The battle scarred architecture is something that will never really go away. I can stop the bleeding, and disinfect the wounds, but there will always be evidence of the battle.

That scarring makes the system hard to understand. It complicates the job of adding features and fixing bugs. It decreases the effectiveness of the developers who work on FitNesse. And though I work hard to massage the scars and bandage the wounds, the war goes on.

But I can keep the CRAP out! I can keep the code so clean and simple at the micro level, that the poor folks who try to make sense out of the macro scale aren’t impeded by huge deeply nested functions that aren’t tested!

Think of it this way. CRAP is disease at the cellular level. CRAP is a rot so pervasive that it can infest every nook and cranny of the system. My system may have scars, but it’s not diseased! In fact, despite the evidence of battles long past, the FitNesse code is very healthy.

And I aim to keep it that way.

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“CRAP is a metric that is applied to each function in the system. The formula for CRAP is: CRAP = comp(f)2. X (1 – cov(f)/100)3. + comp(f)” It have helped me a lot. I have confusion aabout this logic.