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The Cost of Indirection in Rust

56 points

by sebastianconcpt

3 days ago

| past

| 9 comments

| blog.sebastiansastre.co

| HN

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cwillu

1 hour ago

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> Maintainability and understandability only show up when you’re deliberate about them. Extracting meaning into well-named functions is how you practice that. Code aesthetics are a feature and they affect team and agentic coding performance, just not the kind you measure in the runtime.

> And be warned: some will resist this and surrender to the convenience of their current mental context, betting they’ll “remember” how they did it. Time will make that bet age badly. It’s 2026 — other AI agents are already in execution loops, disciplined to code better than that.”

Hard disagree: separating code from its context is exactly how you end up in the situation of needing to “remember”. Yes, helper functions and such can be useful for readability, but it's easy to overdo it and end up with incomprehensible ravioli code that does nothing terribly complicated in a terribly complicated manner.

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schubart

45 minutes ago

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I’m familiar with spaghetti code and with lasagna code (too many layers) but I’m curious: what’s ravioli code?

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p1necone

3 minutes ago

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Each part of the codebase is a separate self contained module with its own wrapping (boilerplate), except there's like 30 of them and you still have to understand everything as a whole to understand the behaviour of the system anyway.

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tartoran

34 minutes ago

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Think of what ravioli are and apply that to the same code analogy as spagetti or lassagna. The code is split in tiny units and that creates too much indirection, a different indirection than spagetti or ravioli. The architecture feels fragmented even though there's nothing wrong with each piece.

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bombela

2 hours ago

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I think this long post is saying that if you are afraid that moving code behind a function call will slow it down, you can look at the machine code and run a benchmark to convince yourself that it is fine?

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layer8

1 hour ago

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I think it’s making a case that normally you shouldn’t even bother benchmarking it, unless you know that it’s in a critical hot path.

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ekidd

2 hours ago

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We have been able to automatically inline functions for a few decades now. You can even override inlining decisions manually, though that's usually a bad idea unless you're carefully profiling.

Also, it's pointer indirection in data structures that kills you, because uncached memory is brutally slow. Function calls to functions in the cache are normally a much smaller concern except for tiny functions in very hot loops.

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thezipcreator

12 minutes ago

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seems pointless to extract `handle_suspend` here. There are very few reasons to extract code that isn't duplicated in more than one place; it's probably harder to read to extract the handling of the event than to handle it inline.

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kstrauser

6 minutes ago

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One huge one is so that you can test it in isolation.

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Sytten

2 hours ago

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Also to note that the inline directive is optional and the compiler can decide to ignore it (even if you put always if I remember)

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armchairhacker

47 minutes ago

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A nitpick I have with this specific example: would `handle_suspend` be called by any other code? If not, does it really improve readability and maintainability to extract it?

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rudolph9

25 minutes ago

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The idea is that performance isn’t a reason not to do it. Other considerations may cause you to choose inline, but performance shouldn’t be one of them.

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cat-whisperer

3 hours ago

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I wouldn't have agreed with you a year ago. async traits that were built with boxes had real implications on the memory. But, by design the async abstraction that rust provides is pretty good!

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Scubabear68

2 hours ago

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A function call is not necessarily an indirection. Basic premise of the blog is wrong on its face.

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hrmtst93837

22 minutes ago

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People new to Rust sometimes assume every abstraction is free but that's just not the case, especially with lifetimes and dynamic dispatch. Even a small function call can hide allocations or vtable lookups that add up quickly if you're not watching closely.

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alilleybrinker

2 hours ago

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Did you read the article? The author makes exactly that point.

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slopinthebag

2 hours ago

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Cool article but I got turned off by the obvious AI-isms which, because of my limited experience with Rust, has me wondering how true any of the article actually is.

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ramon156

2 hours ago

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I don't see anything wrong code-wise, but it's definitely an odd way of making an accumulator. Maybe I'm pedantic