Object Mentor Blog: We must ship now and deal with consequences

We must ship now and deal with consequences

Uncle Bob — Thu, 15 Oct 2009 06:17:00 -0500

Martin Fowler has written a good blog about technical debt. He suggests that there are two axes of debt: deliberate and prudent. This creates four quadrants: deliberate-prudent, deliberate-imprudent, inadvertent-prudent, and inadvertent-imprudent. I agree with just about everything in his blog except for one particular caption…

Inadvertent-Imprudent Debt.

There is more of this debt than any other kind. It is all too common that software developers create a mess and don’t know they are doing it. They have not developed a nose that identifies code smells. They don’t know design principles, or design patterns. They think that the reek of rotten code is normal, and don’t even identify it as smelling bad. They think that their slow pace through the thick morass of tangled code is the norm, and have no idea they could move faster. These people destroy projects and bring whole companies to their knees. Their name is Doom.

Deliberate-Imprudent Debt.

There is a meme in our industry (call it the DI meme) that tells young software developers that rushing to the finish line at all costs is the right thing to do. This is far worse than the ignorance of the first group because these folks willfully create debt without counting the cost. Worse, this meme is contagious. People who are infected with it tend to infect others, causing an epidemic of deliberately imprudent debtors (sound familiar?) The end result, as we are now all know, is economic catastrophe, inflation (of estimates) and crushing interest (maintenance) payments. They have become death, the destroyer of worlds.

Inadvertent-Prudent Debt.

This is something of an oxymoron. Ironically, it is also the best of all possible states. The fact is that no matter how careful we are, there is always a better solution that we will stumble upon later. How many times have you finished a system only to realize that if you wrote it again, you’d do it very differently, and much better?

The result is that we are always creating a debt, because our hindsight will always show us a better option after it is too late. So even the best outcome still leaves us owing. (Mother Earth will eventually collect that debt!)

Deliberate-Prudent Debt.

This is the quadrant that I have the biggest problem with. And it is this quadrant in which Martin uses the caption I don’t like. The Caption is: “We must ship now and deal with consequences.”

Does this happen? Yes. Should it happen? Rarely, yes. But it damned well better not happen very often, and it damned well better not happen out of some misplaced urge to get done without counting the cost.

The problem I have with this quadrant (DP) is that people who are really in quadrant DI think they are in DP, and use words such as those that appear in the caption as an excuse to rack up a huge imprudent debt.

The real issue is the definition of the word: Imprudent.

So let me ask you a question. How prudent is debt? There is a very simple formula for determining whether debt is prudent or imprudent. You can use this formula in real life, in business, and in programming. The formula is: Does the debt increase your net worth, and can you make the payments?

People often focus on the first criterion, without properly considering the second. Buying a house is almost certain to increase your net worth despite the debt (though lately…). On the other hand, if you cannot make the payments, you won’t keep that house for long. The reason for our current economic woes has a lot to do with people trying to increase their net worth despite the fact that they couldn’t afford the payments. (indeed, they were encouraged by a meme very similar to the DI meme!)

Bad code is always imprudent.

Writing bad code never increases your net worth; and the interest rate is really high. People who write bad code are like those twenty-somethings who max out all their credit cards. Every transaction decreases net worth, and has horrendous consequences for cash flow. In the end, the vast bulk of your effort goes to paying the interest (the inevitable slow down of the team as they push the messes around). Paying down the principle becomes infeasible. (Just the way credit card companies like it.)

Some Suboptimal Design Decision are Prudent Debt.

But most are not. Every once in awhile there is a suboptimal design decision that will increase the net worth of the project by getting that project into customer’s hand’s early.

This is not the same as delivering software that is under-featured. It is often prudent to increase the net worth of a project by giving customers early access to a system without a full and rich feature set. This is not debt. This is more like a savings account that earns interest.

Indeed, this is one reason that most technical debt is imprudent. If you are truly concerned about getting to market early, it is almost always better to do it with fewer features, than with suboptimal design. Missing features are a promise that can be kept. Paying back suboptimal designs creates interest payments that often submerge any attempts at payback and can slow the team to the breaking point.

But there are some cases where a sub-optimal design can increase your net worth by allowing you to deliver early. However, the interest rate needs to be very low, and the principle payments need to be affordable, and big enough to pay back the debt in short order.

What does a low interest rate mean? It means that the sub-optimal design does not infiltrate every part of your system. It means that you can put the sub-optimal design off in a corner where it doesn’t impact your daily development life.

For example, I recently implemented a feature in FitNesse using HTML Frames. This is sub-optimal. On the other hand, the feature is constrained to one small part of the system, and it simply doesn’t impact any other part of the system. It does not impede my progress. There is no mess for me to move around. The interest rate is almost zero! (nice deal if you can get it!)

Implementing that feature with ajax is a much larger project. I would have had to invest a great deal of time and effort, and would have had to restructure massive amounts of the internal code. So the choice was a good one.

Better yet, the customer experience has pretty much been a big yawn. I thought people would really like the feature and would drive me to expand upon it. Instead, the customer base has virtually ignored it.

So my solution will be to pay back this debt by eliminating the feature. It was a cheap experiment, that resulted in my not having to spend a lot of time and effort on a new architecture! Net worth indeed!

But it might have gone the other way. My customers may have said: “Wow, Great! We want more!” At that point it would have been terrible to expand on the HTML Frames! That decision would have been in the DI quadrant. Deliberate imprudence! Rather, my strategy would have been to replace the suboptimal Frames design of the feature with an isolated ajax implementation, and then to gradually migrate the ajax solution throughout the project. That would have been annoying, but loan payments always are.

Summary

So, don’t let the caption in the DP quadrant be an excuse. Don’t fall for the DI meme that says “We just gotta bite the bullet”. Tread very carefully when you enter the DP quadrant. Look around at all your options, because it’s easy to think you are in the DP quadrant when you are really in the DI quadrant.

Remember: Murphy shall send you strong delusion, that you should believe you are in DP; so that you will be damned in DI.

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