John Carmack on mutable variables • Hacker News Board

Re: John Carmack on mutable variables

#271

Post by LogicHound » Fri, Oct 31, 2025, 1:42 PM UTC

mrsmrtss wrote: post #232

LogicHound wrote: post #209

Earlier quoted context omitted.

The issue is that I dislike the overall mentality of just adding a bunch of language features. Things just seem to be dumped in each release and I think to myself "When I am going to use that?". > Would you say that these samples show no benefit to using the "is" operator? I didn't say no benefit . I said dubious benefit . I didn't really want to get into discussing specific operators, but lets just use your date exa…

I agree that they should not add new stuff lightly, but the "is" operator actually should be looked together with switch expression in the context of pattern matching. How else could you enable powerful and succint pattern matching in c#?

Arguments about whether the is and switch operators should exist is missing the forest for the trees. I am sure there are circumstances where it very useful.

It isn't any one language feature it is the mentality of both the developer community and Microsoft.

> I agree that they should not add new stuff lightly

It seems though kinda do though. I am not the first person to complain that they add syntactic sugar that doesn't really benefit anything.

e.g. https://devclass.com/2024/04/26/new-c-12-feature-proves-cont...

I have a raft of other complaints outside of language features. Some of these are to do with the community itself which only recognise something existing when Microsoft has officially blessed it, it is like everyone has received the official permission to talk about a feature. Hot Reload was disabled in .NET 6 IIRC for dubious reasons.

Re: John Carmack on mutable variables

#272

Post by bmitc » Fri, Oct 31, 2025, 1:42 PM UTC

lopatin wrote: post #12

How fast this got to the top, you would think John Carmack just invented nuclear fusion.

People worship this guy, but other than being a good C++ graphics programmer, it isn't clear what he's actually done.

Re: John Carmack on mutable variables

#273

Post by nyrp » Fri, Oct 31, 2025, 1:43 PM UTC

Is he referring to something specific with "true" iterative calculations vs. plain old iterative ones, assuming they are in some way "non-true" or less "true"? Like, avoiding i+=x in favor of ++i or something? Or maybe am I just tired today.

Re: John Carmack on mutable variables

#274

Post by johnisgood » Fri, Oct 31, 2025, 1:44 PM UTC

keeda wrote: post #17

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…

We are still living with the hangover of C, which was designed for the resource-starved machines of eons ago, and whose style later languages felt they had to copy to get any kind of adoption. (And as you point out, that is how things turned out.) My bet is functional programming will become more and more prevalent as people figure out how to get AI-assisted coding to work reliably. For the very reasons you stated, f…

Just use OCaml in which you can mix imperative, functional, and OOP. I use all of them in a single codebase, whichever, wherever appropriate.

Re: John Carmack on mutable variables

#275

Post by chongli » Fri, Oct 31, 2025, 1:45 PM UTC

AaronAPU wrote: post #267

This would require coming up with an order of magnitude more variable names which is just unnecessary cognitive load.

No, not at all. You still have the advantages of scopes, name shadowing, namespaces, and collection types. If your language supports them, you can also use algebraic data types to further reduce the number of names you need to deal with.

Re: John Carmack on mutable variables

#276

Post by bmitc » Fri, Oct 31, 2025, 1:45 PM UTC

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…

I get your sentiment, but I side on it's infuriating that it's taken this long. Lol.

F# is wonderful. It is the best general purpose language, in my opinion. I looked for F# jobs for years and never landed one and gave up. I write Rust now which has opened up the embedded world, and it's nice that Rust paid attention to F# and OCaml.

Re: John Carmack on mutable variables

#277

Post by ape4 » Fri, Oct 31, 2025, 1:46 PM UTC

rendaw wrote: post #188

EastLondonCoder wrote: post #128

After a 2 year Clojure stint I find it very hard to explain the clarity that comes with immutability for programmers used to trigger effects with a mutation. I think it may be one of those things you have to see in order to understand.

I think the explanation is: When you mutate variables it implicitly creates an ordering dependency - later uses of the variable rely on previous mutations. However, this is an implicit dependency that isn't modeled by the language so reordering won't cause any errors. With a very basic concrete example: x = 7 x = x + 3 x = x / 2 Vs x = 7 x1 = x + 3 x2 = x1 / 2 Reordering the first will have no error, but you'll get t…

I would be nicer if you gave x1 and x2 meaningful names

Re: John Carmack on mutable variables

#278

Post by bmitc » Fri, Oct 31, 2025, 1:47 PM 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…

F# is not a pure functional language. It is a functional-first language that does imperative and OOP better than imperative and OOP languages.

You can program F# just like you would Python, and it will be more readable, concise, performant, and correct.

Re: John Carmack on mutable variables

#279

Post by ufo » Fri, Oct 31, 2025, 1:47 PM UTC

nyrp wrote: post #273

Is he referring to something specific with "true" iterative calculations vs. plain old iterative ones, assuming they are in some way "non-true" or less "true"? Like, avoiding i+=x in favor of ++i or something? Or maybe am I just tired today.

I think he's just saying that mutation is ok if it's something loopy, like changing the loop counter or updating some running sum. So both i+=1 and ++i are fine.

Re: John Carmack on mutable variables

#280

Post by bmitc » Fri, Oct 31, 2025, 1:48 PM UTC

pvdebbe wrote: post #196

christophilus wrote: post #89

Earlier quoted context omitted.

F# isn’t purely functional, though, and strikes a nice balance. I just don’t really like the .NET ecosystem, being 100% Linux these days, as it always seems slightly off to me somehow.

Same. I strikes me a great shame that there aren't great F#-like languages that targeted the JVM.

Really? What's wrong with .NET? It's one of the nicest cross-platform platforms out there. What Microsoft has done with it is amazing.