'in->func()->out' work cleanly for physical engineering domains because blocks of computations (or functions) have no memory basically. There's no DB and there's usually no global state in the way you'd mean with classes. I've observed that when you work on complex software, you could play by the ear to enforce 'high cohesion and loose coupling' up to the point to where you've now got a data store holding system state. Based on what I've worked on, this system state is actually user data and then some derivative of the system's own interaction on this user data, both of which are necessary for the 'continuity of system runtime'. For example, working with redis as the primary data store, I extracted different types of redis calls for specific keys, (like set [specific_key], get [specific key], etc.) into functions, then I put these functions into a StateStore class so I can simply call StateStore.get_user_data() or StateStore.set_user_data() etc from any module across the entire system. From first principles, this is great modularity and high cohesion but it's very tight coupling around a single module i.e. StateStore. Any change in that module means I'd have to find all references for that updated function and cross check for any contract violations. It's difficult for me to see how software can purely be 'High Cohesion and Loose Coupling' regardless of paradigm or architectural pattern. There's always gonna be an unavoidable and inevitable principle violation that's simple a result of a large complex system actually doing many little things that come together to actually do one big thing. The software itself, no matter how complex, IS the blackbox where data goes in and something comes out but that's the user perspective not ours as the programmer. I think the idea I'm trying to hint at is that software cannot have every module independent of every other one. That's impossible. If nothing depended on anything else, the system wouldn't do anything. Rather than have every module know redis keys, States tore actually concentrates coupling into one place, which is exactly what high cohesion tries to accomplish. I think that's the idea I'm chasing.