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Cognitive load is what matters

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1455 points nromiun | 2 comments | 30 Aug 25 12:58 UTC | HN request time: 0s | source
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exclipy ◴[30 Aug 25 20:51 UTC] No.45077894[source]▶
This was my main takeaway from A Philosophy Of Software Design by John Ousterhout. It is the best book on this subject and I recommend it to every software developer.

Basically, you should aim to minimise complexity in software design, but importantly, complexity is defined as "how difficult is it to make changes to it". "How difficult" is largely determined by the amount of cognitive load necessary to understand it.

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bsenftner ◴[30 Aug 25 20:58 UTC] No.45077954[source]▶
Which is why I consider DRY (Don't Repeat Yourself) to be an anti-rule until an application is fairly well understood and multiple versions exist. DO repeat yourself, and do not create some smart version of what you think the problem is before you're attempting the 3rd version. Version 1 is how you figure out the problem space, version 2 is how you figure out your solution as a maintainable dynamic thing within a changing tech landscape, and version 3 is when DRY is look at for the first time for that application.
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zahlman ◴[30 Aug 25 21:50 UTC] No.45078299[source]▶
DRY isn't about not reimplementing things; it's about not literally copying and pasting code. Which I have seen all the time, and which some might find easier now but will definitely make the system harder to change (correctly) at some point later on.
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1. YZF ◴[30 Aug 25 23:06 UTC] No.45078797{3}[source]▶
But sometimes you should copy and paste code because those difference pieces of code can evolve independently. Knowing when to do this and when not to do this is what we do and no rule can blindly say one way or the other.

Even the most obvious of functions like sin() and cos() may in some circumstances warrant a specialized implementation. Sure, for most stuff you should not have 10 copies of those all over the place. But sometimes you might.

DRY is a bad rule. The more appropriate rule is avoid duplicating code when not doing so results something better. I.e. judgement always trumps rules.

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2. Pannoniae ◴[01 Sep 25 11:53 UTC] No.45091977[source]▶
Oh yeah, 100% this, I made a homemade sincos implementation which roughly returns the right result roughly all the time. It's nice because I don't care about the exact answer (it's for randomly rotating angles for generating caves, terrain generation) and it's like 5x as fast as doing it properly!