I’m electronifying my notes from conferences and such. Here’s my notes from Jim Weirich’s SOLID design principles in Ruby talk from eRubyCon 2009.

1.) Single Responsibility Principle
a class should have 1 reason to exist
describe the purpose of your class in a single sentence (you shouldn’t need and/or)

2.) Open/Closed Principle
you should be able to extend a class’ behavior without modifying it

3.) Liskov Substitution Priniciple
require no more, promise no less

4.) Interface Segregation Principle

5.) Dependency Inversion Principle
depend on abstractions, not concrete-tions

** Note that my notes are a little bit shotty, because the days prior to the conference I was totally totally strapped at work and thus rest-deprived.