Thursday, 22 December 2011

Why we must write clean code

Engineers are often (rightly) accused of being pedantic. We insist that we use an integer rather than a short or that we should or should not use a pattern. The sales type people don't understand this and will tell us that as long as the customer sees a system that does what they want, they couldn't give two hoots (or 2 dollars) for how it is implemented. This might seem like a pragmatic approach since in a sense that is true but sadly there are a few assumptions in that statement that need to be exposed and which reinforce the need for strict coding practices. Firstly, the life of software is usually much longer than it is assumed. Look at Windows XP for instance, when it was first released in 2001, MS would have a plan that in 5 years, it would be pretty much replaced by whatever their next OS was going to be (Vista or Windows 7 perhaps). In other words, don't get crazy with it, if a bug will survive 5 years, we can leave it in and then fix it later. In fact, XP still holds around 33% of internet connected machines 11 years later. It is still being used and the bugs that might have laid unlikely for 5 years are much more likely to surface over 11 years. In a similar way, do we really design software for 10 or 20 years? If we designed a car to survive that long, we would have to be very careful about all components yet in software we can still be quite glib about the level of quality that is acceptable. Secondly, it is quite glib to say something like, "as long as the customer gets what he wants", both because over time this will prove less true and also because it is not as black-and-white as that. MS Word pretty much OK but there are things I don't like about it and I live with them - it is not either perfect or useless. The level to which we can achieve this 'perfection' however is important in people trusting our software. Also, this acceptance is based on functionality as much as reliability and there is every chance after a while that a customer will want to change something, a good test of how well the software was originally written. Another reason why we should strive for quality is to ease maintenance. We have staff turnover and we have to change and fix things. There is nothing worse than being presented with an obvious defect but being totally overwhelmed by the code we have to look through to find the cause of the defect. This is why we should keep our objects classified specifically and deliberately. Data objects contain properties to describe their data and little else. Control objects provide methods to do stuff and should not generally be persisted. Interface objects translate between specific systems and can be added or removed as the boundaries change. We have probably all been in the situation where we notice an issue in code and are told it is so low a priority that we should not fix it (partly this is because of the build time overhead - something we should consider) but as with rust, what starts with a small bit can grow and grow until a full rewrite or re-factor is required. We must be careful that we don't break code that might be 'wrong' but works because something else takes account of its wrongness but at the same time, we should feel at ease making code more readable and obvious. Of course, the best way to do this is to get the code correct in the first place so it doesn't need to be changed and this again requires company buy-in because it involves training and reviews. It requires keen eyes that can spot where mistakes are creeping in and finding ways to mitigate the risks. Even subtle coding styles can introduce errors so sometimes we might require very high-level training about separation of concerns, correct use of comments and ensuring that we are using tools that make this easy to do so the time required doesn't become unacceptable. We need to treat our software with more respect and we need processes and people who understand that so that what we produce is still running as expected in 10 or 20 years time, hopefully with a lot of repeat work!
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