Michael Feathers on Functional Code

Michael Feathers wrote Functional Code is Honest Code. I will take away questions from this article.

He starts out

It’s hard to change things that you don’t understand — you can try, but you’ll often fail.

I can not agree more to it. But I see that this is hard in our industry, the playfulness when writing code seems often to be more important.

My take away Question

I might not know the definitions of OO and Functional good enough, but to me the following seem a bit too strict.

So many of the techniques around gaining testability involve parameterizing classes and methods so that all of the inputs and outputs are explicit and mockable under test.

I would call that dependency injection. And it has the following result.

You pass in a reference to that capability as a constructor or method argument. This makes an OO system, broadly functional.

Is passing in a reference or in other words a dependency, what distinguishes OO code from functional code? Mmmh, I always thought it's just a technique applied whereever.