The problem with your desire is that the most cutting edge OOP paradigm is event-sourcing, which is essentially functional. Event sourcing isn't a clearly defin

The problem with your desire is that the most cutting edge OOP paradigm is event-sourcing, which is essentially functional. Event sourcing isn't a clearly defined pattern, but it kinda blends functional ideas, "given a state and a change, i'll give you a new state" such that your system will give a non-deterministic new state based on a change. That's de facto functional programming. Having said that, the leanest system will be reference types under the hood, as for example, the C# stack frame is limited to 1mb and can't contain your app's entire state. So we arrive at today's cutting edge which is F#, Clojure, etc. that are functional wrappers around heap-based lookups.