Skip to content(if available)orjump to list(if available)

Ruby 4.0.0 Preview2 Released

Ruby 4.0.0 Preview2 Released

21 comments

·November 18, 2025

ksec

Nothing about Fibres and Async from Samuel Williams ?

falcor84

Any particular changes of interest?

sdwolfz

The NEWS link details a bit more:

https://github.com/ruby/ruby/blob/v4_0_0_preview2/NEWS.md

What is interesting to me is the `Ractor.shareable_proc` changes that solved a bug for a use case I was having. And in general fixes for Ractors make them more appealing to use right now, even though they have not removed the `Experimental` flag from them. They are still missing a built-in concurrency primitive like channels or a lock free queue; I'm curious what they will settle on, Ractor::Port is nice but not enough.

dudeinjapan

ZJIT is supposed to be an improvement on YJIT. I'm happy to get any free performance improvements!

The Ruby Ractor (Actor) interface is now completely changed to use a Ractor::Port class, mirroring IPC (inter-process communication) semantics. Ractors were added in 3.0 as a way to get around the GVL/GIL, but having N number of Ruby interpreters running in a Ruby process which would enable executing on N cores at once. For me, hot take but Ractors don't seem to offer major advantages over plain-ol' copy-on-write (COW) forking.

The one "big" feature was supposed to be namespaces, which apparently have now been renamed to Ruby::Box (https://docs.ruby-lang.org/en/master/box_md.html). From what I can glean from the Ruby issue tracker, it appears this feature has been radically descoped, primarily because it had performance impacts, but also, I think probably there are realistic concerns about fit with the existing ecosystem. Unlike Javascript/Python, Ruby has never used "modules" for code isolation--everything is loaded into the global namespace (the "global dumping ground" as I call it.) Now the Box feature is only enabled with an environment variable RUBY_BOX=1

https://bugs.ruby-lang.org/issues/21311

shevy-java

I don't think it has really descoped. They just want the transition to be smooth. So they start slowly. The lead japanese dev will most likely in 2026 go for more extension, and I also think this kind of has to be synced a bit with ractor (I think?).

Ractor is also strange. Do many people use ractors? I rarely see them used in actual ruby code out there. Right now it seems to me as if ractors are used by only ... say ... 1% or fewer of the ruby developers out there. A bit more than refinement users ... :P

dudeinjapan

Ractors have promise but the implementations up till now haven't had strong concurrency safety. It seems in the latest release some of the heavy-hitter contributors like Jean Boussier (byroot) have taken a detailed look at Ractors and started to clean things up.

https://byroot.github.io/ruby/performance/2025/05/24/unlocki...

frou_dh

I'm happy if that feature has been descoped because when I last read up on it, it seemed like it was being ramrodded in by an inner circle who were hardly interested in constructive criticism even from other Ruby core maintainers.

dudeinjapan

I had a talk with Matz 1-on-1 about 6 months back and expressed my doubts about namespaces :) He's a nice guy, he just smiled.

lloydatkinson

I didn't know Ruby has three different JITs

Lio

I was actually hoping it would be four JITs and we'd get Tenderlove's tiny FFI JIT too.

https://railsatscale.com/2025-02-12-tiny-jits-for-a-faster-f...

shevy-java

Mostly the newer ones try to improve the older ones.

I guess at some later point one will dominate and the others will go sleep mode. Just like in the movie Highlander - there can only be one. (I couldn't name offhand which JIT is the main one right now ... I always think it is from Takashi Kokubun but that may now be outdated. MJIT YJIT ZJIT HUJIT WAJIT WTFJIT GRANDMAJIT - too many JITs.)

hartator

Yes, specially ZJIT is news to me.

shevy-java

It is 4.0.0 largely because matz created ruby 30 years ago.

matz is no longer the youngest - although he does look young, he is already 60 years old. He also said he has a retirement plan, e. g. avoiding a situation such as when Guido quit (or semi-quit) from Python (due to fatigue/frustration; Guido is not 100% retired but he is also not necessarily the solo-design-dev either, so it is a bit of a semi-retirement). So we won't know how long matz will be the lead designer of ruby - and who will succeed. Which may be reason to worry depending on who it would be. Imagine DHH takes over - man, there would be an insta-exodus of people ...

So while this release does not have a lot of content as such, one thing that is quite big, even though right now it is not, is Ruby::Box. There are many who don't understand it. The thing is ... I understand the use cases for it. I was not involved in any way with regards to its design, mind you - that was mostly a japanese-group in design. But there are objective use cases for it.

Many years ago I recall on IRC (we oldschool people used IRC back in the pre-discord stone age) some C# hacker said he won't use ruby because there are no strong namespaces, that is, someone else can just overwrite things and then nothing works. Although I think he was a drama guy, and any "danger" to be minimal, objectively he has had a point, simply because ruby had no strong concept of isolation here. Lateron there came refinements. Now refinements are strange, because while I think the use case makes sense, the syntax is strange. Syntax is one huge reason why I do not use refinements; but also because I try to avoid putting my own modifications all over the place, largely because I'd have to distribute that too, and also because modifying core classes, while that has a use, should not be done excessively, IMO.

Ruby::Box kind of builds on that and makes the refinement use case more generic (eventually; I am aware that right now this is not the case but you need a transition stage. Syntax-wise Ruby::Box is also weird, so hopefully the syntax gets easier too, but I instantly understood the use cases. Many people don't, in particular about 95% who demanded a name change away from Namespace to something else, really don't understand the underlying use case.)

Now - making isolated per-project changes is not the only use case. For instance, ractors could be simplified if you know that there are separate ruby processes; ruby threads probably too. These I consider secondary benefits though (and yes, that may be far in the future, who knows; when python removed its GIL though, it put ruby under pressure, aka shape-up-or-go-extinct mode).

One thing I would complain a lot is that on rubygems.org, before RubyCentral went shopify-controlled-only, that people would occupy namespaces. Such as Configuration. I wanted to have a project called Configuration so I can do Configuration.new or Configuration.parse_this_file(). This is possible of course, but when it comes to distributing code, who owns that toplevel namespace? Normally the one who occupied the name first on rubygems.org, sort of. Via Ruby::Box, it should be possible to have ownerships. This could be strong or weak; weak as a hint, aka "psych is owned by ruby core ownershiper but it can be modified", or strong aka making it immutable. Both have use cases. Could also be both. Having this more organized would be really convenient for developers. I would not have to worry whether anyone else uses that "namespace". And of course we need a way to query this state from within ruby code too aka, say immutable:

"If psych is owned by ruby-core, continue to use it."

psych (for yaml) is not a good example here but you can think of any other namespace where you may only want to consider some gems/projects but not others. (Again, the use case may differ between strong and weak ownership, but the thing is that this is an improvement over the prior status quo.)

There are several additional use cases to be had but I'll stop here. What I find strange is that many people who complain, don't refer to the old issues and discussions. We had discussions before refinements were added. About 80% of the people involved, DON'T EVEN KNOW THESE OLD DISCUSSIONS. Either they have dementia, or these are young ruby users who never were active in the old days. It's very strange.

I am not saying all is perfect about Ruby::Box, in particular syntax-wise I'd like improvements, but many people don't seem to understand the use cases, and this is very very strange.

werdnapk

Ruby dev since 2000 and looks like refinements have been available since 2.4. I just used them for the first time this year. Definitely not a go to feature for me, but it was nice the feature was available.

dudeinjapan

Ruby::Box in its current form seems to radically miss the mark. Any namespace paradigm only has utility if it is widely adopted across the ecosystem. Javascript did this with ES modules 10 years ago--it IS possible--but it takes a ton of buy-in and effort from the community to achieve it.

I just don't think Ruby has this "burning need" to have namespaces/modules/erm... "boxes". So we're likely to end up with sporadic usage of Boxes leading to inconsistent behavior.

thebigkick

Curious, why would DHH trigger a mass exodus?

brigandish

The Ruby "community" has long been dogged by politics and culture war stuff. This comment[0] on a flagged submission has lots of links for getting up to speed.

Maybe they're right, there would be an exodus, I just wonder if other languages' communities will want the trouble. The Japanese Rubyists don't care for a second, a nice by-product of Japanese insularity. Ruby would continue in Japan just fine without westerners, don't worry.

[0] https://news.ycombinator.com/item?id=45379652

throwaway48921

I'd much prefer Jeremy Evans[0] taking over rather than DHH. Jeremy is a Ruby core committer (and much more pleasant person), unlike DHH.

[0] - https://github.com/jeremyevans

flykespice

Would you keep using a programming language leaded by a racist? I wouldn't

npteljes

If programming is just my hobby, then maybe. But would you, for example, quit your current job and look for another, just to change the programming language? I know I'm not that sort of person.

dudeinjapan

This is exactly why we shouldn't use KKScript either. Plus it has 1-based array indexes.