Little robot (III): Dependency inversion

As I wrote some posts ago, I received an assignment, and I decided to do both in Java and in Ruby. When doing in Ruby I wanted to make sure I was able to test the UI, and not only the engine. For doing that, I chose to fake the console interaction (both stdin and stdout). I didn’t consider dependency inversion.

Sometimes a higher level class A has to invoke methods in a lower level class. Let’s say this lower level class tends to be class B. Typical approach (non DI) is to make class A depend on class B. Dependency inversion is to make class B implement some contract associated with class A (the dependency is inverted).

I think I’m still in the process of converting from Java(where DI and interfaces is compulsory) to Ruby. With Ruby is much easier to fake classes B and don’t even think about inversion while developing class A. Maybe I should have done my class more testable. But I didn’t realize it until in a different selection process I was asked when to use Dependency Inversion in Ruby.