Less Magical Numbers

A quick look at how we can better comment "magical numbers" and constants in code

Transcript

1. Lloyd Moore, President Lloyd@CyberData-Robotics.com www.CyberData-Robotics.com Toward Less Magical Magic Numbers
2. In the “dark times” we represented constants like this: double x = 2.718; We eventually started calling this a “magic number”, as it is just a number that has to be correct for the program to work.
3. In time it was determined this was bad and we added more information: // The natural log of 1, e1 const double e = 2.718281; This is better, but for many applications it still isn’t good enough. Information is still missing:  Where did this number come from?  Why this particular precision?  Is there a traceability requirement to the specifications?
4. Even when not formally required, having more information makes the number less magical: // The natural log of 1, e1 // Source: https://en.wikipedia.org/wiki/Natural_logarithm // 12 decimal places required for algorithm foo() // per requirement ABC-33920. const double e = 2.718281828459;
5. But what if it is just a number that someone made up?: // Developer discretion const double x = 2.718; Then say so with some type of flag. This will let the reader know the number doesn’t have any particular significance!
6. Real World Implications: This presentation is a result of a real world issue from an aerospace project. A constant had two different levels of precision between the flight software and the IV&V software, resulting in a failed verification. It took minutes to find the difference and a month to sort out value which was needed!
7. Questions?