Yes, I see people thinking the first one is easier because they're thinking that you only do f1() once, instead of doing it thousands of times. In reality, both are equally easy to write, but it's hard for some people to shift their thinking from the work the computer does to the work the programmer does.
That's really interesting. So the point is that they're effectively the same in the sense of the amount of work necessary to write the code, and putting in the effort to code the first one might be premature optimisation if running f1() thousands of times isn't actually an issue, or that you might need to debounce f1(), or guard against side effects, which is 'harder'.
I think I'd find it really hard to let go of the idea that my code might be doing something wasteful like calling a function it doesn't really need to call. Maybe it's because I've been coding since the early 90s when clock cycles and memory actually mattered a bit more. It's certainly given me something to think about. Thanks.
Well, it's a good gut reaction to have. As you wrote yourself "In reality, both are equally easy to write" - therefore the first one is a good default to assume, because in some cases it may actually matter.
If you choose good default, then you won't spend any more time thinking about it; if you have bad defaults, then you will have to figure out where the slowdown comes from and eliminate it.
So, if I understand your point correctly, you mean that newer programmers, who are struggling to find any solution at all, would go for the (subjectively) easier one, i.e. the one with f1() outside of the loop?
I agree they would go for the easier one, but I don't understand why they would perceive the first version to be easier. And even if they would, why is it bad?