Hacker News Reader

Comment by tested23 | Hacker News Reader

Ugh, you are right but then someone comes and uses this to rationalize not including things like map, filter and reduce in a language because they are supposedly too complicated and you can just do it with a for loop

View on HN

I work in a Rust codebase that uses a lot of functional functions, and I’ll say this: on average the imperative style takes less lines of code and less indentation. I also find it more readable personally, and idiomatic.

Just because we’re on the topic of performance: the rust optimizer can sometimes generate better code if you use map / filter / etc. The slice iterator in any context is a huge win over manual array iteration because it only needs to do bounds checking once.

Javascript (v8, last I checked) is the opposite. Simple for loops almost always outperform anything else.

I've seen cases where an iterator was better, but I've also seen gains from using an imperative loop with manual indexing. Loop conditions and the occasional assertion can be enough to elide bounds checks. (Though sometimes the compiler gets too paranoid about integer overflow.)

Most of the time you should just write whatever's clear/convenient but sometimes it's worth trying both and scrutinizing godbolt.

This is premature optimization imo. Unless you’re using par_iter

Without knowing the domain, you have no way of knowing that.

It’s also much easier to stick to for() loops in javascript as you code than it is to rewrite everything later when tuning for performance. If that’s something you expect to need to do.

Functional iteration is good for the same reason we use for loops over while loops, and while loops over goto: they are more constrained, more clearly communicate intent, and are therefore easier to reason about.

Sure but it’s easy to go overboard with this stuff. Reduce (fold) especially can be pretty hard to read in hairy situations.

My general rule is that if you need fewer lines of code to implement your logic with a simple for loop, you probably should.

Yeah, I agree with that. Especially reduce/fold, which I find is almost always better written as loop. Filter would be a good example of the opposite for me: almost always much clearer written functionally.

I find I frequently use a combination - use map/filter to setup an iterator, and then reduce it in a loop.

I suspect this has more to do with the lack of first-class sequence comprehensions in the syntax. If you had to write imperative style, but all loops were HOFs, it would hardly be ergonomic, either. OTOH a good query language is much more readable.

Reply on news.ycombinator.com