John Carmack on mutable variables

Post by Fire-Dragon-DoL » Fri, Oct 31, 2025, 7:18 AM UTC

josephg wrote: post #7

munchler wrote: post #2

> Making almost every variable const at initialization is good practice. I wish it was the default, and mutable was a keyword. It's funny how functional programming is slowly becoming the best practice for modern code (pure functions, no side-effects), yet functional programming languages are still considered fringe tech for some reason. If you want a language where const is the default and mutable is a keyword, try…

> If you want a language where const is the default and mutable is a keyword, try F# for starters. I switched and never looked back. Rust is also like this (let x = 5; / let mut x = 5;). Or you can also use javascript, typescript and zig like this. Just default to declaring variables with const instead of let / var. Or swift, which has let (const) vs var (mutable). FP got there first, but you don't need to use F# to…

Post by qmmmur » Fri, Oct 31, 2025, 7:40 AM UTC

nielsbot wrote: post #44

hyperhello wrote: post #3

> I wish it was the default, and mutable was a keyword. I wish the IDE would simply provide a small clue, visible but graphically unobtrusive, that it was mutated . In fact, I end up wishing this about almost every language feature that passes my mind. For example, I don't need to choose whether I can or can't append to a list; just make it unappendable if you can prove I don't append. I don't care if it's a map, lis…

I use Swift for work. The compiler tell you this. If a mutable variable is never mutated it suggests making it non-mutable. And vice versa.

Post by v9v » Fri, Oct 31, 2025, 7:46 AM UTC

cogman10 wrote: post #25

the__alchemist wrote: post #14

Earlier quoted context omitted.

I think it's because (I'm looking at Haskell in particular) there are a lot of great ideas implemented in them, but the purity makes writing practical or performant time-domain programs high friction. But you don't need both purity and the various tools they provide. You can use the tools without the pure-functions model. In particular: My brain, my computing hardware, and my problems I solve with computers all feel…

My problem with functional languages is there never seems to be any easy way to start using them. Haskell is a great example here. Last time I tried to learn it, going on the IRC channel or looking up books it was nothing but a flood of "Oh, don't do that, that's not a good way to do things." It seemed like nothing was really settled and everything was just a little broken. I mean, Haskell has like what, 2, 3, 4? Maj…

Post by worthless-trash » Fri, Oct 31, 2025, 7:51 AM UTC

hyperhello wrote: post #3

> I wish it was the default, and mutable was a keyword. I wish the IDE would simply provide a small clue, visible but graphically unobtrusive, that it was mutated . In fact, I end up wishing this about almost every language feature that passes my mind. For example, I don't need to choose whether I can or can't append to a list; just make it unappendable if you can prove I don't append. I don't care if it's a map, lis…

Post by christophilus » Fri, Oct 31, 2025, 7:54 AM UTC

jandrewrogers wrote: post #16

munchler wrote: post #2

> Making almost every variable const at initialization is good practice. I wish it was the default, and mutable was a keyword. It's funny how functional programming is slowly becoming the best practice for modern code (pure functions, no side-effects), yet functional programming languages are still considered fringe tech for some reason. If you want a language where const is the default and mutable is a keyword, try…

Pure functional works great until it doesn't. For a lot of systems-y and performance-oriented code you need the escape hatches or you'll be in for a lot of pain and annoyance. As a practical observation, I think it was easier to close this gap by adding substantial functional capabilities to imperative languages than the other way around. Historically, functional language communities were much more precious about the…