[jcromartie]

> Then, when the urge to rewrite something strikes, you can just rewrite that one component, knowing that everything else should work just fine.

I'm pretty sure this was the promise of OOP, too. Or at least the promise of the OOP that was sold to me in (limited) school and on the job.

[naradaellis]

A main reason that it is hard or impractical to refactor a part of an OO system is that you cannot reason about its side-effects on the rest of the system without scouring all of its source.

When you are guaranteed that a subsystem has no side effects, you can gut its internals and as long as the interface behaves the same - your system will behave the same.

edit: a _stateful_ OO system anyway.