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Rewriting Bun in Rust

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Re: Rewriting Bun in Rust

#101

Post by dabinat »

> This Rust rewrite would've taken a team of engineers with full-context on the codebase a year of work. With 1 engineer using Fable & closely monitoring Claude Code, we went from start to 100% of the test suite passing on all platforms in 11 days.

This is impressive from a technological standpoint, but it does gloss over the fact that it would have cost $165k in tokens were Bun not part of Anthropic.

The comparison here isn’t completely fair - it would take a small team a year to port it if they spent $0 extra on it.

I’d be interested to see a comparison between spending $165k in 11 days on Claude vs splitting that between 50 people over 11 days for a line-by-line rewrite of the Zig code. I suspect Claude might be faster and therefore cheaper, but maybe not by a lot.

Re: Rewriting Bun in Rust

#102

Post by achristmascarl »

I was fairly skeptical about the rewrite when news about it first started going around, and I still don't plan on switching anything to use the Bun rewrite anytime soon, but I appreciate how detailed and well-written the blog post is; it also seems to be primarily human-authored, in my opinion, which is refreshing.

The most significant revelation for me was that Claude Code has been using the rewrite without much fanfare since June 17th.

Re: Rewriting Bun in Rust

#103

Post by incognito124 »

himata4113 wrote: post #75

They didn't mention the cost of this. Assuming mythos was somewhat involved I'd extrapolate this as: 128 x20 max accounts needed which comes at $25.6k or over 75k in api costs. For 75k you can hire a team of engineers that would produce a better result with sematic conversion and other tricks used in porting from language A to language B at the cost of maybe taking 1 month instead of 10 days. I will be a lot more exc…

It states $165k in the article

Re: Rewriting Bun in Rust

#104

Post by pjjpo »

giancarlostoro wrote: post #31
YuechenLi wrote: post #29

>Combined with the Rust rewrite, ICU changes, and identical code folding, Bun's binary size shrinks by ~20% on Linux & Windows. People who are surprised by this probably has not seen what Zig code actually looks like. Zig's explicitness and lack of abstraction have a real cost that it is basically one of the most verbose programming languages I've ever seen, it's somehow even more verbose than Go. Basic features of m…

> Ironically, Zig is a programming language that's probably best written by LLMs, since they can tolerate actually tolerate the verbosity. Rust in my opinion feels the same.

I have found LLMs struggle with Rust's constraints - they are optimized to produce code that passes the tests, not necessarily good code. So instead of working out lifetimes and borrowing, it will be happy to copy a buffer many times without thought. This means I have to still go through line by line to review and often rewrite either by hand or with another LLM iteration.

There may be some prompting that can help with this but I suspect there is a fundamental tension between writing working code vs good code in LLMs. Go is popular for being simple, making it easy to jump in and write something fast and stable - minimizing the gap between working and good code probably helps out the LLMs a lot.

Re: Rewriting Bun in Rust

#105

Post by tekacs »

dabinat wrote: post #101

> This Rust rewrite would've taken a team of engineers with full-context on the codebase a year of work. With 1 engineer using Fable & closely monitoring Claude Code, we went from start to 100% of the test suite passing on all platforms in 11 days. This is impressive from a technological standpoint, but it does gloss over the fact that it would have cost $165k in tokens were Bun not part of Anthropic. The comparison…

I feel like a core difference is that the AI implementor can get cheaper/faster (and indeed _uniformly_ better), whereas it would be very difficult for the same humans to do so.

Even if this is not the right answer today, it can at the very least serve as a herald of a possible future, no?

Re: Rewriting Bun in Rust

#106

Post by Philpax »

dabinat wrote: post #101

> This Rust rewrite would've taken a team of engineers with full-context on the codebase a year of work. With 1 engineer using Fable & closely monitoring Claude Code, we went from start to 100% of the test suite passing on all platforms in 11 days. This is impressive from a technological standpoint, but it does gloss over the fact that it would have cost $165k in tokens were Bun not part of Anthropic. The comparison…

I think it'd take you at least eleven days to meaningfully coordinate 50 people!

Re: Rewriting Bun in Rust

#107

Post by Buttons840 »

ameliaquining wrote: post #94
Buttons840 wrote: post #78

I've always felt [0] the people who created Bun had, as their first and foremost goal, a desire to use Zig--and that's great, I like Zig, I like when people build things their own way. However, I've been skeptical of using Bun, because I want a project whose first and foremost goal is to build good tools that achieve the objectives of the project. It reminds me of asking game developers: Do you want to build a game ,…

So does that mean the rewrite made you less skeptical?

Yeah, I guess. Now it appears to be a project run by Anthropic and I'm sure the real focus is on making money--which is still slightly different than having the focus be on making the best tool.

Re: Rewriting Bun in Rust

#108

Post by typ »

YuechenLi wrote: post #29

>Combined with the Rust rewrite, ICU changes, and identical code folding, Bun's binary size shrinks by ~20% on Linux & Windows. People who are surprised by this probably has not seen what Zig code actually looks like. Zig's explicitness and lack of abstraction have a real cost that it is basically one of the most verbose programming languages I've ever seen, it's somehow even more verbose than Go. Basic features of m…

Abstraction doesn't necessarily lead to a smaller binary. Much of the bloat in modern software is indeed due to (bad) abstractions.

Re: Rewriting Bun in Rust

#109

Post by Jenk »

dabinat wrote: post #101

> This Rust rewrite would've taken a team of engineers with full-context on the codebase a year of work. With 1 engineer using Fable & closely monitoring Claude Code, we went from start to 100% of the test suite passing on all platforms in 11 days. This is impressive from a technological standpoint, but it does gloss over the fact that it would have cost $165k in tokens were Bun not part of Anthropic. The comparison…

$165k won't get you far on salaried engineers. There's every chance that 1 engineer, assuming Anthropic employs them, is on $500k or more. Assuming average of $336k in that pool of 50 engineers, then for 11 days for 50 engineers you've spent $710k[0].

Salary info: https://www.levels.fyi/companies/anthropic/salaries/software...

[0]The maths I used (posting because I'm tired and prone to mistakes):

    $336,000 / 260 (working days of the year) = ~$1,292.
    $1,292 * 11 * 50 = ~$710,769

Re: Rewriting Bun in Rust

#110

Post by Philpax »

simonw wrote: post #93
Philpax wrote: post #5

Without commenting on Bun itself as a project, or the nature of the rewrite, it can't be good for Zig that a naive rewrite away from it fixed memory leaks, improved stability, shrunk binary size by 20%, and improved performance by 5%.

I don't think it's care to categorize this as "a naive rewrite away from [Zig]" - Jarred has been immersed in this project for five years, got to benefit from everything he learned along the way and spent $165,000 of tokens on the most advanced coding LLM anyone has access to. I expect if he'd spent $165,000 running Fable against the Zig version he could have got a 5% performance improvement, too.

Oh, I have no doubt that they could have extracted those gains from Zig! My point is more that, from a relatively naive line-to-line port, they were able to claim these benefits without much effort.

It's not great for Zig if you have to put in more work to end up at the same place efficiency-wise, especially for a language marketed at people who like to get the most out of their metal.

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