Post #495378

2025-11-13 13:28 UTC

🦀 I&#39;ve improved the implementation behind all the string formatting macros in Rust: println!(), panic!(), format!(), write!(), log::info!(), and so on. (That is, everything based on format_args!().) They will compile a bit faster, use a bit less memory while compiling, result in smaller binaries, and produce more efficient code! 🎉 &#39;Hello world&#39; compiles 3% faster and a few bigger projects like Ripgrep and Cargo compile 1.5% to 2% faster. And those binaries are roughly 2% smaller. 🎊 This change will be available in Rust Nightly tomorrow, and should ship as part of Rust 1.93.0 in January. #rustlang

Replies (15)

@Mara@hachyderm.io 2025-11-13 14:04

Note that there are also lots of programs where this change makes very little difference. Many benchmarks show just 0.5% or 0.1% improvement, or simply zero difference. The most extreme case is the `large-workspace` benchmark, which is a generated benchmark with hundreds of crates that each just have a few println!() statements. That one now compiles 38% faster and produces a 22% smaller binary.

Open ##1364948
@Sobex@social.sciences.re 2025-11-13 13:29

@Mara Is there any write-up of the underlying dark magic (or light magic, if that's the work of a Jedi)

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@sminez@hachyderm.io 2025-11-13 13:30

@Mara Awesome! 🎉 Do you have a link the PR(s) that landed this? I'd love to see what the changes look like 😄

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@lorepozo@tech.lgbt 2025-11-13 14:23

@Mara I remember your writeup a couple years ago on this, it looked like such a daunting task! Thank you for pursuing this!

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@michalfita@mastodon.social 2025-11-13 14:45

@Mara Thank you very much for your hard work on this!

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@PerlPlayer@mastodon.social 2025-11-13 15:36

@Mara great job. Thank you 🥳

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@natty@astolfo.social 2025-11-13 14:17

@Mara@hachyderm.io Wait the magic trick is turning an array of arrays into a tiny interpreted language? :wlfAngel:

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@vivasupeR@mastodon.social 2025-11-13 16:13

@Mara Great reduction of waste. are there any downsides to the new approach? for example, a flaw or copy error in a shared macro could potentially be more harmful. on the other hand, such a flaw would now be harder to hide. I wonder if these considerations have already been made, or if I’m just overthinking it.

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@aras@mastodon.gamedev.place 2025-11-13 17:07

@Mara excellent work!

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@ahoneybun@hachyderm.io 2025-11-13 19:20

@Mara nice!

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@bascule@mas.to 2025-11-13 21:00

@Mara I've heard several people say the old implementation was incredibly arcane and hadn't changed much since the pre-1.0 days. Regardless kudos to you for rewriting it and improving the performance, one of those wins almost every program benefits from

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@ekhjarta@mastodon.nu 2025-11-14 08:27

@Mara wow. Great work!

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@bshn@hachyderm.io 2026-02-02 08:46

@Mara ✊✊✊

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@RuchiraSDatta@mathstodon.xyz 2026-02-04 07:27

@Mara Thank you!

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@niconiconi@mk.absturztau.be 2025-11-13 21:50

@Mara@hachyderm.io I thought the performance gain was negligible, then I saw the original implementation needed to toggle the SSE register just to print "Hello, world" on the screen. Certainly an important optimization regardless of CPU time spent.

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