Smalltalk Best Practice Patterns

by Kent Beck

• Rates of change—A simple criteria I use all the time is checking rates of change. I learned this criteria from something Brad Cox said a long time ago. I’ve since generalized it to—don’t put two rates of change together. Don’t have part of a method that changes in every subclass with parts that don’t change. Don’t have some instance variables whose values change every second in the same object with instance variables whose values change once a month. Don’t have a collection where some elements are added and removed every second and some elements are added and removed once a month. Don’t have code in an object that has to change for every piece of hardware, and code that has to change for every operating system. How do you avoid this problem? You got it, lots of little pieces.

I did not understand the reason for this completely.