The point of the async interview series, in the end, was to help figure out what we should be doing next when it comes to Async I/O. I thought it would be good then to step back and, rather than interviewing someone else, give my opinion on some of the immediate next steps, and a bit about the medium to longer term. I’m also going to talk a bit...

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Since we created the Rust teams, I have been serving as lead of two teams: the compiler team and the language design team (I’ve also been a member of the core team, which has no lead). For those less familiar with Rust’s governance, the compiler team is focused on the maintenance and implementation of the compiler itself (and, more recently, the...

I wanted to write a post that looks back over 2020 from a personal perspective. My goal here is to look at the various initiatives that I’ve been involved in and try to get a sense for how they went, what worked and what didn’t, and also what that means for next year. This post is a backdrop for a #niko2021 post that I plan to post sometime...

I’ve got an announcement to make. As of Jan 4th, I’m starting at Amazon as the tech lead of their new Rust team. Working at Mozilla has been a great experience, but I’m pretty excited about this change. It’s a chance to help shape what I hope to be an exciting new phase for Rust, where we grow from a project with a single primary sponsor...

Hey folks! As part of the Async Vision Doc effort, I’m planning on holding two public drafting sessions tomorrow, March 23rd: March 23rd at noon ET (click to see in your local timezone) March 23rd at 5pm ET (click to see in your local tomezone) During these sessions, we’ll be looking over the status quo issues and writing a story or two! If you’d...

I’m scheduling two more public drafting sessions for tomorrow, Match 26th: On March 26th at 10am ET (click to see in your local timezone), we will be working on writing a story about the challenges of writing a library that can be reused across many runtimes (rust-lang/wg-async-foundations#45); On March 26th at 2pm ET (click to see in your local...

Ryan Levick and I are hosting a number of public drafting sessions scheduled this week. Some of them are scheduled early to cover a wider range of time zones. When Who Topic Tue at 14:30 ET Niko wrapping C++ async APIs in Rust futures and other tales of interop Wed at 10:00 ET Niko picking an HTTP library and similar stories Wed at 15:00 ET Niko...

I’ve been working on the Rust project for just about ten years. The language has evolved radically in that time, and so has the project governance. When I first started, for example, we communicated primarily over the rust-dev mailing list and the #rust IRC channel. I distinctly remember coming into the Mozilla offices1 one day and brson...

My week is very scheduled, so I am not able to host any public drafting sessions this week – however, Ryan Levick will be hosting two sessions! When Who Topic Thu at 07:00 ET Ryan The need for Async Traits Fri at 07:00 ET Ryan Challenges from cancellation If you’re available and those stories sound like something that interests you, please join...

This is an exciting week for the vision doc! As of this week, we are starting to draft “shiny future” stories, and we would like your help! (We are also still working on status quo stories, so there is no need to stop working on those.) There will be a blog post coming out on the main Rust blog soon with all the details, but you can go to the...

Ryan Levick and I are going to be hosting more Async Vision Doc Writing Sessions this week. We’re not organized enough to have assigned topics yet, so I’m just going to post the dates/times and we’ll be tweeting about the particular topics as we go. When Who Wed at 07:00 ET Ryan Wed at 15:00 ET Niko Fri at 07:00 ET Ryan Fri at 14:00 ET Niko If...

My week is very scheduled, so I am not able to host any public drafting sessions this week – however, Ryan Levick will be hosting two sessions! When Who Wed at 07:00 ET Ryan Fri at 07:00 ET Ryan If you’re available and those stories sound like something that interests you, please join him! Just ping me or Ryan on Discord or Zulip and we’ll send...

The Async Vision Doc effort has been going now for about 6 weeks. It’s been a fun ride, and I’ve learned a lot. It seems like a good time to take a step back and start talking a bit about the vision doc structure and the process. In this post, I’m going to focus on the role that I see vision docs playing in Rust’s planning and decision making,...

This Monday I am starting something new: a monthly meeting called the “Cross Team Collaboration Fun Times” (CTCFT)1. Check out our nifty logo2: The meeting is a mechanism to help keep the members of the Rust teams in sync and in touch with one another. The idea is to focus on topics of broad interest (more than two teams): Status updates on...

You may have heard that the Rust 2021 Edition is coming. Along with my daughter Daphne, I have recorded a little song in honor of the occasion! The full lyrics are below – if you feel inspired, please make your own version!1 Enjoy! Video Lyrics (Spoken) Breaking changes where no code breaks. Sounds impossible, no? But in the Rust language, you...

The second “Cross Team Collaboration Fun Times” (CTCFT) meeting will take place one week from today, on 2021-06-21 (in your time zone)! This post describes the main agenda items for the meeting; you’ll find the full details (along with a calendar event, zoom details, etc) on the CTCFT website. Afterwards: Social hour After the CTCFT this week, we...

Hey everyone! At the CTCFT meeting this Monday (2021-06-21), we’re going to try a “social hour”. The idea is really simple: for the hour after the meeting, we will create breakout rooms in Zoom with different themes. You can join any breakout room you like and hangout. The themes for the breakout rooms will be based on suggestions. If you have an...

The next “Cross Team Collaboration Fun Times” (CTCFT) meeting will take place one week from today, on 2021-07-19 (in your time zone)! What follows are the abstracts for the talks we have planned. You’ll find the full details (along with a calendar event, zoom details, etc) on the CTCFT website. Mentoring Presented by: doc-jones The Rust project...

Hold the date! The next Cross Team Collaboration Fun Times meeting will be 2021-09-20. We’ll be using the “Asia-friendly” time slot of 21:00 EST. What will the talks be about? A detailed agenda will be announced in a few weeks. Current thinking however is to center the agenda on Rust interest groups and domain working groups, those brave...

As the web site says, Rust is a language empowering everyone to build reliable and efficient software. I think it’s precisely this feeling of empowerment that people love about Rust. As wycats put it recently to me, Rust makes it “feel like things are possible that otherwise feel out of reach”. But what exactly makes Rust feel that way? If we can...

The next “Cross Team Collaboration Fun Times” (CTCFT) meeting will take place next Monday, on 2021-09-20 (in your time zone)! This post covers the agenda. You’ll find the full details (along with a calendar event, zoom details, etc) on the CTCFT website. Agenda Announcements Interest group panel discussion We’re going to try something a bit...

RustConf is always a good time for reflecting on the project. For me, the last week has been particularly “reflective”. Since announcing the Rustacean Principles, I’ve been having a number of conversations with members of the community about how they can be improved. I wanted to write a post summarizing some of the feedback I’ve gotten. The...

Over the last few weeks, Tyler Mandry and I have been digging hard into what it will take to implement async fn in traits. Per the new lang team initiative process, we are collecting our design thoughts in an ever-evolving website, the async fundamentals initiative. If you’re interested in the area, you should definitely poke around; you may be...

In the previous post, we uncovered a key challenge for dyn and async traits: the fact that, in Rust today, dyn types have to specify the values for all associated types. This post is going to dive into more background about how dyn traits work today, and in particular it will talk about where that limitation comes from. Today: Dyn traits...

In the previous “dyn async traits” posts, I talked about how we can think about the compiler as synthesizing an impl that performed the dynamic dispatch. In this post, I wanted to start explore a theoretical future in which this impl was written manually by the Rust programmer. This is in part a thought exercise, but it’s also a possible...

In the previous post, I talked about how we could write our own impl Iterator for dyn Iterator by adding a few primitives. In this post, I want to look at what it would take to extend that to an async iterator trait. As before, I am interested in exploring the “core capabilities” that would be needed to make everything work. Start somewhere: Just...

The next “Cross Team Collaboration Fun Times” (CTCFT) meeting will take place next Monday, on 2021-10-18 (in your time zone)! This post covers the agenda. You’ll find the full details (along with a calendar event, zoom details, etc) on the CTCFT website. Agenda The theme for this meeting is exploring ways to empower and organize contributors. (5...

If you’re willing to use nightly, you can already model async functions in traits by using GATs and impl Trait — this is what the Embassy async runtime does, and it’s also what the real-async-trait crate does. One shortcoming, though, is that your trait doesn’t support dynamic dispatch. In the previous posts of this series, I have been exploring...

A quick update to my last post: first, a better way to do what I was trying to do, and second, a sketch of the crate I’d like to see for experimental purposes. An easier way to roll our own boxed dyn traits In the previous post I covered how you could create vtables and pair the up with a data pointer to kind of “roll your own dyn”. After I...

Ever wanted to understand how rustc works? Me too! Doc Jones and I have been talking and we had an idea we wanted to try. Inspired by the very cool Code Reading Club, we are launching an experimental Rustc Reading Club. Doc Jones posted an announcement on her blog, so go take a look! The way this club works is pretty simple: every other week,...

I wanted to write about an idea that’s been kicking around in the back of my mind for some time. I call it view types. The basic idea is to give a way for an &mut or & reference to identify which fields it is actually going to access. The main use case for this is having “disjoint” methods that don’t interfere with one another. This is not a...

The next “Cross Team Collaboration Fun Times” (CTCFT) meeting will take place next Monday, on 2021-11-22 at 11am US Eastern Time (click to see in your time zone). Note that this is a new time: we are experimenting with rotating in an earlier time that occurs during the European workday. This post covers the agenda. You’ll find the full details...

Wow! The response to the last Rustc Reading Club was overwhelming – literally! We maxed out the number of potential zoom attendees and I couldn’t even join the call! It’s clear that there’s a lot of demand here, which is great. We’ve decided to take another stab at running the Rustc Reading Club, but we’re going to try it a bit differently this...

Hi all! Welcome to 2022! Towards the end of last year, Tyler Mandry and I were doing a lot of iteration around supporting “dyn async trait” – i.e., making traits that use async fn dyn safe – and we’re starting to feel pretty good about our design. This is the start of several blog posts talking about where we’re at. In this first post, I’m going...

One of the things people often complain about when doing Async Rust is cancellation. This has always been a bit confusing to me, because it seems to me that async cancellation should feel a lot like panics in practice, and people don’t complain about panics very often (though they do sometimes). This post is the start of a short series comparing...

Last year, we shipped Rust 2021 and I have found the changes to be a real improvement in usability. Even though the actual changes themselves were quite modest, the combination of precise capture closure and simpler formatting strings (println!("{x:?}") instead of println!("{:?}", x)) is making a real difference in my “day to day” life.1 Just...

Last Friday, tmandry, cramertj, and I had an exciting conversation. We were talking about the design for combining async functions in traits with dyn Trait that tmandry and I had presented to the lang team on Friday. cramertj had an insightful twist to offer on that design, and I want to talk about it here. Keep in mind that this is a piece of...

There are two ergonomic features that have been discussed for quite some time in Rust land: perfect derive and expanded implied bounds. Until recently, we were a bit stuck on the best way to implement them. Recently though I’ve been working on a new formulation of the Rust trait checker that gives us a bunch of new capabilities — among them, it...

Rust has been wrestling with coherence more-or-less since we added methods; our current rule, the “orphan rule”, is safe but overly strict. Roughly speaking, the rule says that one can only implement foreign traits (that is, traits defined by one of your dependencies) for local types (that is, types that you define). The goal of this rule was to...

Lately I’ve been diving deep into tokio’s mini-redis example. The mini-redis example is a great one to look at because it’s a realistic piece of quality async Rust code that is both self-contained and very well documented. Digging into mini-redis, I found that it exemplifies the best and worst of async Rust. On the one hand, the code itself is...

You’ve probably heard that the Rust type checker can be a great “co-pilot”, helping you to avoid subtle bugs that would have been a royal pain in the !@#!$! to debug. This is truly awesome! But what you may not realize is how it feels in the moment when this happens. The answer typically is: really, really frustrating! Usually, you are trying to...

As some of you may know, on May 4th Jack Huey opened a PR to stabilize an initial version of generic associated types. The current version is at best an MVP: the compiler support is limited, resulting in unnecessary errors, and the syntax is limited, making code that uses GATs much more verbose than I’d like. Nonetheless, I’m super excited, since...

Have you heard of the Salsa project? Salsa is a library for incremental computation – it’s used by rust-analyzer, for example, to stay responsive as you type into your IDE (we have also discussed using it in rustc, though more work is needed there). We are in the midst of a big push right now to develop and release Salsa 2022, a major new...

In the last few months, Tyler Mandry and I have been circulating a “User’s Guide from the Future” that describes our current proposed design for async functions in traits. In this blog post, I want to deep dive on one aspect of that proposal: how to handle dynamic dispatch. My goal here is to explore the space a bit and also to address one...

Re-reading my previous post, I felt I should clarify why I called it the “soul of Rust”. The soul of Rust, to my mind, is definitely not being explicit about allocation. Rather, it’s about the struggle between a few key values — especially productivity and versatility1 in tension with transparency. Rust’s goal has always been to feel like a...

After my last post on dyn async traits, some folks pointed out that I was overlooking a seemingly obvious possibility. Why not have the choice of how to manage the future be made at the call site? It’s true, I had largely dismissed that alternative, but it’s worth consideration. This post is going to explore what it would take to get...

I’ve been thinking about what “Rust 2024” will look like lately. I don’t really mean the edition itself — but more like, what will Rust feel like after we’ve finished up the next few years of work? I think the answer is that Rust 2024 is going to be the year of “everywhere”. Let me explain what I mean. Up until now, Rust has had a lot of nice...

When I started working on Rust in 2011, my daughter was about three months old. She’s now in sixth grade, and she’s started growing rapidly. Sometimes we wake up to find that her clothes don’t quite fit anymore: the sleeves might be a little too short, or the legs come up to her ankles. Rust is experiencing something similar. We’ve been growing...

Nightly Rust now has support for async functions in traits, so long as you limit yourself to static dispatch. That’s super exciting! And yet, for many users, this support won’t yet meet their needs. One of the problems we need to resolve is how users can conveniently specify when they need an async function to return a Send future. This post...

In the previous post, I introduced the “send bound” problem, which refers to the need to add a Send bound to the future returned by an async function. I want to start talking about some of the ideas that have been floating around for how to solve this problem. I consider this a bit of an open problem, in that I think we know a lot of the...

I previously introduced the “send bound” problem, which refers to the need to add a Send bound to the future returned by an async function. This post continues my tour over the various solutions that are available. This post covers “Trait Transformers”. This proposal arose from a joint conversation with myself, Eric Holk, Yoshua Wuyts, Oli...

One interesting question about async fn in traits is whether or not we should label the trait itself as async. Until recently, I didn’t see any need for that. But as we discussed the question of how to enable “maybe async” code, we realized that there would be some advantages to distinguishing “async traits” (which could contain async functions)...

In today’s lang team design meeting, we reviewed a doc I wrote about temporary lifetimes in Rust. The current rules were established in a blog post I wrote in 2014. Almost a decade later, we’ve seen that they have some rough edges, and in particular can be a common source of bugs for people. The Rust 2024 Edition gives us a chance to address some...

Rust has lots of mechanisms that prevent you from doing something bad. But, right now, it has NO mechanisms that force you to do something good1. I’ve been thinking lately about what it would mean to add “must move” types to the language. This is an idea that I’ve long resisted, because it represents a fundamental increase to complexity. But...

I’ve been thinking about async closures and how they could work once we have static async fn in trait. Somewhat surprisingly to me, I found that async closures are a strong example for where async transformers could be an important tool. Let’s dive in! We’re going to start with the problem, then show why modeling async closures as “closures that...

It’s well known that my blog has some issues. The category links don’t work. It renders oddly on mobile. And maybe Safari, too? The Rust snippets are not colored. The RSS feed is apparently not advertised properly in the metadata. It’s published via a makefile instead of some hot-rod CI/CD script, and it uses jekyll instead of whatever the new...

In a previous post on async closures, I concluded that the best way to support async closures was with an async trait combinator. I’ve had a few conversations since the post and I want to share some additional thoughts. In particular, this post dives into what it would take to make async functions matchable with a type like impl FnMut() -> impl...

I recently posted a draft of an RFC about Return Type Notation to the async working group Zulip stream. In response, Josh Triplett reached out to me to raise some concerns. Talking to him gave rise to a 3rd idea for how to resolve the send bound problem. I still prefer RTN, but I think this idea is interesting and worth elaborating. I call it...

One of Rust’s core principles is “stability without stagnation”. This is embodied by our use of a “release train” model, in which we issue a new release every 6 weeks. Release trains make releasing a new release a “non-event”. Feature-based releases, in contrast, are super stressful! Since they occur infrequently, people try to cram everything...