2009-07-03

Engineers' Stigmergy

Getting some work done on my car, I noticed that the last garage to service it had left a little label on the door pillar with the mileage and type of oil put in last time.

I've done a fair bit of maintenance and porting of long-term applications, the oldest ( aerostructure stress routines at BAE ) were several decades old. In the better code, there are a succession of comments explaining just what you need to find any tricky bits next time you look. In an awful lot of code, there's a record of every file change made, what was done and who did it. In the worst, I've seen lines and lines of comments for functions and operations that no longer exist in the code, or which are blatantly false. I don't care who made a change; I rarely care that someone fixed a bug a year ago - if it is fixed, then it's not a problem, if there's a regression on it, then I'm not likely to come round and mock them.

The garage which serviced my car last year fixed seven or eight little things - I've got the receipt somewhere if I care what exactly - but they only put the one thing that the next maintainer needs as a comment on the car. It's a bit easier to predict what that will be for a mechanic, but it's not impossible for software.


On the other hand, it's interesting to see a series of comments in one of the models which was implemented in Fortran, where every five years or so the sizes of the arrays used goes up as machines get more capable and the code is asked to deal with more complicated models.

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