In recent years my general principle has been to introduce an abstraction (in this case split up a function) if it lowers local concepts to ~4 (presumably based on similar principles to the original post). I’ve taken to saying something along the lines of “abstractions motivated by reducing repetition or lines of code are often bad, whilst ones motivated by reducing cognitive load tend to be better”.

Good abstractions often reduce LOC, but I prefer to think of that as a happy byproduct rather than the goal.

>My principle has always been: “is this part a isolated and intuitive subroutine that I can clearly name and when other people see it they’ll get it at first glance without pausing to think what this does (not to mention reading through the implemention)”.

I hold this principle as well.

And I commonly produce one-liner subroutines following it. For me, 15 lines has become disturbingly long.

I tend toward John Carnack's view. He seemed annoyed that he was being pressed to provide a maximum at all and specified 7000 lines. I don't think I have ever gone that high. But really is just a matter of what you are doing. We expect to reuse things way more often than we actually do. If you wrote out everything you need to do in order and then applied the rule of three to make a function out of everything you did three times, it is very possible you wouldn't remove anything. In which case I think it should just be the one function.

> We expect to reuse things way more often than we actually do.

This is about readability (which includes comprehensibility), not reuse. When I read code from others who take my view, I understand. When I read code from those who do not, I do not, until I refactor. I extract a piece that seems coherent, and guess its purpose, and then see what its surroundings look like, with that purpose written in place of the implementation. I repeat, and refine, and rename.

It is the same even if I never press a key in my editor. Understanding code within my mind is the same process, but relying on my memory to store the unwritten names. This is the nature of "cognitive load".

Yeah, I find extracting code into methods very useful for naming things that are 1) a digression from the core logic, and 2) enough code to make the core logic harder to comprehend. It’s basically like, “here’s this thing, you can dig into it if you want, but you don’t have to.” Or, the core logic is the top level summary and the methods it calls out to are sections or footnotes.