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Comment by diondokter | Hacker News Reader

So on the title, I picked this because it's simply the truth. Since async landed in 2019 or so, not much has changed.

Yes, we can have async in traits and closures now. But those are updates to the typesystem, not to the async machinery itself. Wakers are a little bit easier to work with, but that's an update to std/core.

As I understand it, the people who landed async Rust were quite burnt out and got less active and no one has picked up the torch. (Though there's 1 PR open from some google folk that will optimize how captured variables are laid out in memory, which is really nice to have) Since I and the people I work with are heavy async users, I think it's maybe up to me to do it or at least start it. Free as in puppy I guess.

So yeah, the title is a little baitey, but I do stand behind it.

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Some of the burnout no doubt being due to the catastrophizing of every decision by the community and the extreme rhetoric used across the board.

Great to see people wanting to get involved with the project, though. That’s the beauty of open source: if it aggravates you, you can fix it.

As an example of this, i remember a huge debate at the time about `await foo()` vs `foo().await` syntax. The community was really divided on that one, and there was a lot of drama because that's the kind of design decision you can't really walk back from.

Retrospectively, i think everyone is satisfied with the adopted syntax.

> Retrospectively, i think everyone is satisfied with the adopted syntax.

Maybe it’s a case of agree and commit, since it can’t really be walked back.

Various prominent people have said years after that .await was the correct choice after all

I'm not prominent but I disagreed with it at the time and I was wrong.

I’m curious - why were you wrong? It still seems like a wart to me, all these years later. What am I missing?

Contrast it with async in JS/ES as an example... now combine it with the using statement for disposeAsync instances.

    await using db = await sqlite.connect(await ctx.getConfig("DB_CONN"));

It's not so bad when you have one `await foo` vs `foo.await`, it's when you have several of them on a line in different scopes/contexts.

Another one I've seen a lot is...

    const v = await (await fetch(...)).json();

Though that could also be...

    const v = await fetch(...).then(r => r.json());

In any case, it still gets ugly very quickly.

I’ve never in my life used JS, so I’ll have to take your word for it.

It's a language I'm familiar with that uses the `await foo` syntax and often will see more than one in a line, per the examples given. C# is the most prominent language that has similar semantics that I know well, but is usually less of an issue there.

I'll give my two cents here. I work with Dart daily, and it also uses the `await future` syntax. I can cite a number of ergonomic issues:

```dart (await taskA()).doSomething() (await taskB()) + 1 (await taskC()) as int ```

vs.

```rust taskA().await.doSomething() taskB().await + 1 taskC().await as i32 ```

It gets worse if you try to compose:

```dart (await taskA( (await taskB( (await taskC()) as int )) + 1) ).doSomething() ```

This often leads to trading the await syntax for `then`:

```dart await taskC() .then((r) => r as i32) .then(taskB) .then((r) => r + 1) .then(taskA) .then((r) => r.doSomething()) ```

But this is effectively trading the await structured syntax for a callback one. In Rust, we can write it as this:

```rust taskA(taskB(taskC().await as i32).await + 1).await.doSomething() ```

Two spaces before a line make it a code block literal

  This is a code block

HN has never used markdown so the triple-tick does nothing but create noise here.

Thnaks for heads up, I'll keep this in mind in the future.

I was a proponent of the postfix macro solution. `.await!` or `.await!()`, essentially. The idea was that this could be generalized, it was closer to existing syntax, etc.

I was worried about features that I still don't love like `.match` etc (I'm more open to these now).

Post-fix macros would have been very complex. Scoping alone is complex.

`.await` kinda just works. It does everything you want and the one cost is that it looks like a property access but it isn't. A trivial cost in retrospect that I was a huge baby about, and I'll always feel bad about that.

The postfix macro does sound like a better solution tbh. Did you write the static assertions crate? If so, thank you. I’m a daily user.

Ha, no, I did not write that crate. I think my use of this username probably predates rust, certainly that crate.

Postfix macros had some very tricky issues and it would have delayed things a lot to figure out the right resolution.

I was initially very against postfix await and I was wrong. It's great.

It makes sense that there was a huge debate, because the postfix .await keyword was both novel (no other languages had done it that way before) and arguably the right call. Of course, one can argue that the ? operator set a relevant precedent.

I think it's partially accurate, and partially a consequence of how async fractures the design space, so it will always feel like a somewhat separate thing, or at least until we figure out how to make APIs agnostic to async-ness.

I am a beginner to Rust but I've coded with gevent in Python for many years and later moved to Go. Goroutines and gevent greenlets work seamlessly with synchronous code, with no headache. I know there've been tons of blog posts and such saying they're actually far inferior and riskier but I've really never had any issues with them. I am not sure why more languages don't go with a green thread-like approach.

One of Rust's central design goals is to allow zero cost abstractions. Unifying the async model by basically treating all code as being possibly async would make that very challenging, if not impossible. Could be an interesting idea, but not currently tenable.

One problem I have with systems like gevent is that it can make it much harder to look at some code and figure out what execution model it's going to run with. Early Rust actually did have a N:M threading model as part of its runtime, but it was dropped.

I think one thing Rust could do to make async feel less like an MVP is to ship a default executor, much like it has a default allocator.

They could still come in a step short of default executor and establish some standard traits/types that are typical across executors.

By providing a default, I think you're going to paint yourself into a corner. Maybe have one of two opt-in executors in the box... one that is higher resource like tokio and one that is meant for lower resource environments (like embedded).

Rust originally came with a green thread library as part of its primary concurrency story but it was removed pre-1.0 because it imposed unacceptable constraints on code that didn’t use it (it’s very much not a zero cost abstraction).

As an Elixir + Erlang developer I agree it’s a great programming model for many applications, it just wasn’t right for the Rust stdlib.

Because they have their own drawbacks. To make them really useful, you need a resizable stack. Something that's a no-go for a runtime-less language like Rust.

You may also need to setup a large stack frame for each C FFI call.

Claim-1: the async versus sync distinction cannot be meaningfully dissolved at the programmer level.

Claim-2: async versus sync is a fundamental division in CS

Discuss amongst yourselves. I lean towards thinking both are probably true (P~70%, P~90%)

See: “What Color is Your Function?” by Bob Nystrom (2015). https://journal.stuffwithstuff.com/2015/02/01/what-color-is-...

As an uninterested 3rd party, it’s a wild exaggeration

> So on the title, I picked this because it's simply the truth. Since async landed in 2019 or so, not much has changed.

Hi. The article calls Rust async an MVP. You should expect strong reactions when you frame it like that.

"MVP" has a generally understood meaning; distorting that is unhelpful and confusing. Rust's async was not an MVP when it was released in 2019. It was the result of a lot of earlier work.

Rust async: (a) works well for a lot of people and orgs in production settings and (b) is arguably better designed than most (all?) other async implementations. Calling it an MVP is far from "simply the truth". It is an opinion -- and frankly a pretty clickbaity one. I appreciate your article's attention to detail, but the title is straight up shameful sensationalism.

I strive to not reflexively defend the status quo, but I get really chafed when people conveniently blur the difference between fact and opinion.

Please argue on narrowest correct claims available. The current title overstates your claims and undermines its overall credibility. Your central claim (as I read it) is that for embedded software there are opportunities for async improvement in Rust. Yeah this might sound boring, but I think it's accurate.

My other main criticism of your article is when it claims Rust async breaks the "zero cost abstraction" principle. I don't buy this claim, because you do not show that hand rolling the code provides the same guarantees. A lot of people misunderstand what "zero cost" means; your article wouldn't be the first to give the wrong impression.

Writing is hard (different audiences bring different backgrounds), and I commend anyone who puts their ideas out into the world. Please take this as constructive feedback: please agree or disagree with me on the merits. Ask and engage where I'm unclear.

> Rust's async was not an MVP when it was released in 2019

The team literally described it as such.

One of the main architects of Rust’s async/await, withoutboats, left a comment on lobsters:

> It's just the truth. Neither in the language design nor in the compiler implementation has hardly any progress been made in the now 7 years since we shipped the MVP. The people primarily involved in delivering the MVP all become less active in the project around the same time and delivery since then has stalled out.

> I hope this person receives the support to do this work.

Rust’s async is great, and I feel you around some of the less informed criticisms. But it’s been called an MVP for a decade now, it’s not an insulting characterization. Just because it’s been an MVP does not mean it’s not good or useful.

Arguably the state it was left in is the state that was sufficient for the needs of all adopters. Don't fix something if it ain't broke. I know it's been sufficient for fuchsia which did a lot of the initial investment. The types of improvements described in the post tend to only matter at scale or in embedded use cases. No one from those realms has decided it was a sufficiently important problem to prioritize solving until now so it didn't get solved.

Even if MVP is the correct term for its current state, it has a connotation to it which less informed folks will take away the wrong meaning from, so perhaps it's not useful to continue to propagate it even if true.

> No one from those realms has decided it was a sufficiently important problem to prioritize solving until now so it didn't get solved.

This is both true and not true. It's no secret that the async ecosystem has had deep social rifts for a very long time, and that's made it very tough to actually make progress by anyone, regardless of the desire to.

It is true that async massively gave a boost to Rust's adoption, and it is good enough for many users. It is a monumental technical achievement. At the same time, that doesn't mean it's perfect.

Sorry, I was too harsh. Or to be more precise: I should not have directed my criticism only at this particular blog post. This topic is a hot mess. Yes, even the 2019 blog post announcing Async Rust [1] used the phrase:

> On this coming Thursday, November 7, async-await syntax hits stable Rust, as part of the 1.39.0 release. This work has been a long time in development -- the key ideas for zero-cost futures, for example, were first proposed by Aaron Turon and Alex Crichton in 2016! -- and we are very proud of the end result. We believe that Async I/O is going to be an increasingly important part of Rust's story.

> While this first release of "async-await" is a momentous event, it's also only the beginning. The current support for async-await marks a kind of "Minimum Viable Product" (MVP). We expect to be polishing, improving, and extending it for some time.

> Already, in the time since async-await hit beta, we've made a lot of great progress, including making some key diagnostic improvements that help to make async-await errors far more approachable. To get involved in that work, check out the Async Foundations Working Group; if nothing else, you can help us by filing bugs about polish issues or by nominating those bugs that are bothering you the most, to help direct our efforts.

---

MVP originated from the lean startup world: the core meaning is to build the smallest thing that validates demand. Async-await (a-a) was so much more than that.

Whoever wrote the blog post wrote "MVP" which leaves a reader wondering: are those scare quotes? [2]

Nice a-a was "in the air" since Go shipped it in 2009. Compiled state machines hit the scene not long after: C# in 2012, Clojure in 2013. So demand did not need validation. As I understand it, probably the biggest driver for Rust a-a was to provide a common foundation for work going forward.

The effort and thinking that went into async/await probably blows away 99.9% of MVPs released out into the world! And I don't think it would be crazy to say Rust's a-a was better than ~80% of even "1.0" products.

I don't want to get bogged down in mere definitions... I'm emphasizing the primary emotional vibe. Using MVP (or "MVP") is a surefire way to conjure the wrong emotional valence. It invites confusion and downplays years of incredible work.

My feeling is that original blog post used that framing because the Rust team is famously open to taking however much time is needed to get things as close to perfect as they know how.

[1]: https://blog.rust-lang.org/2019/11/07/Async-await-stable/

[2]: https://en.wikipedia.org/wiki/Scare_quotes

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