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John Carmack on mutable variables

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498 points azhenley | 1 comments | 31 Oct 25 02:34 UTC | HN request time: 0s | source
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hyperhello ◴[31 Oct 25 03:00 UTC] No.45767863[source]▶
> 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, list, set, listOf, array, vector, arrayOf, Array.of(), etc unless it's going to get in my way because I have ten CPU cores and I'll optimize the loop when I need to.

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estimator7292 ◴[31 Oct 25 03:40 UTC] No.45768166[source]▶
Your IDE probably supports this as an explicit action. JetBrains has a feature that can find all reads and writes to a variable
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Denvercoder9 ◴[31 Oct 25 07:48 UTC] No.45769329[source]▶
It also has the ability to style mutated variables differently.
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1. greenicon ◴[31 Oct 25 08:40 UTC] No.45769672[source]▶
Yes, depending on your highlighting scheme. Not every highlighting scheme shows this by default, unfortunately.

To me, this seems initially like some very minor thing, but I find this very helpful working with non-trivial code. For larger methods you can directly discern whether a not-as-immutable-declared variable behaves immutable nonetheless.