[Darmani]

Pretty surprising -- I had much the opposite experience.

On our last product, we decided to start switching from Typescript to Rust on the backend because we got tired of crashes. I consider that to be one of the greatest technical mistakes I've made ever, as our productivity slowed massively. I'll just share two time-draining issues that only occur in Rust: (1) Writing higher-order functions (e.g.: a function to open a database connection, do something, and then close it -- yes, I know you can use RAII for this particular example), which is trivial in Haskell and TypeScript and JavaScript and C++ and PHP, turned out to be so impossible in Rust [even after asking Rust-expert friends for help], that I learned to just give up and never try, though it sometimes worked to write a macro instead. (2) It's happened many times that I would attempt a refactoring, spend all day fixing type errors, finally get to the top-level file, get a type error that's actually caused somewhere else by basic parts of the design, and conclude the entire refactoring I had attempted is impossible and need to revert everything.

On top of that, Rust is the only modern language I can name where using a value by its interface instead of its concrete type lies somewhere between advanced and impossible, depending on what exactly you're doing.

I came away concluding that application code (as opposed to systems or library code) should, to a first approximation, never be written in Rust.

[atombender]

I'm not a Rust expert by any means, but I'm surprised to hear this. In my Rust code, doing anything with a database connection is not at all different from, say, Go or TypeScript.

For example, I use the deadpool-postgres crate for database pooling. Getting a connection looks like this:

    let conn = self.pool.get().await?;

Because of RAII, you don't need a higher-order function helper, but if you really wanted to make one:

    async fn with_conn<T>(
        &self,
        f: impl AsyncFnOnce(Object<Manager>) -> Result<T>,
    ) -> Result<T> {
        let conn = self.pool.get().await?;
        f(conn).await
    }

Now you can do:

    with_conn(|conn| async move {
      conn.query("SELECT 1")  // Or whatever
    }).await

If you know TypeScript, this shouldn't be too difficult to read or write. The gnarliest stuff here is knowing the type signature of the function argument; because of async, it must be AsyncFnOnce, for one, and you need to know that the type that the deadpool crate returns is called Object<Manager> (which doesn't sound like a connection, to be fair). Determining the exact concrete type to match type constraints on is sometimes a chore, but TypeScript is surely no different here!

If you don't know Rust too well, the "move" part will be a little mysterious, to be sure.

[Darmani]

Just investigated -- looks like this works now! Yay!

For this family of examples, had been completely stymied by AsyncFnOnce not being released yet. IIRC it had been in the works for several years, was still an experimental feature when I was trying to use it, and I gave up after much frustration at trying to get a version of Rust with experimental features working under devenv (nix).

A subtraction then to my frustrations with Rust -- though I'd still be very wary of doing this, having seen how fragile higher-order functions have been in the past.

[atombender]

That explains it. I think async closures were stabilized a year ago. Before that, you'd have needed to write out the async signature as non-async with futures (that's what async is syntactic sugar for, anyway). Something like:

    f: impl FnOnce(Object<Manager>) -> impl Future<Output = Result<T>>

[pjmlp]

I appreciate Rust for making affine types mainstream, and having at least the C++ community start caring about security, even if half hearted.

However I share your conclusion, outside scenarios where having automated resource management as the main approach is either technically impossible, or a waste of time trying to change pervasive culture, I don't see much need for Rust.

In fact those that write comments about wanting a Rust but without borrow checker, the answer already exists.

[Darmani]

I think Rust would be fine for application code if it kept the borrow checker, but had greater allowance for dynamically-sized variables, or even garbage collection. The reason calling things through an interface is so tough in Rust is because doing so requires having a pointer to a value of unknown size, which involves either heap allocation or alloca(), neither of which are very happy in Rust. Many of the other things I complained about are also downstream of this decision. Affine types are useful both in high-level state management as well as in low-level memory management. But it's Rust's focus on static memory layout that really cements it as a low-level systems language, not its inclusion of borrowing.

Way back as an undergrad in 2011, I contributed to Plaid, a JVM language whose main feature is based on affine and linear types. I'm one of the very few people in the world who knew what borrowing is before Rust had it. So I know first-hand that borrow-checking is perfectly compatible with garbage collection.

[pjmlp]

Exactly, and that is why after Rust's break into mainstream, several garbage collected languages are trying to mix advanced type systems with their approach to garbage collection (GC, RC, a mix of both, whatever).

This is also not strange for those in the Rust community with type systems experience, hence the Roadmap 2026 proposals for a more ergonomic experience.

Thus we have Linear Haskell, Swift 6 ownership, D ownership, Koka, Hylo, Chapel, OxCaml, Scala Capabilities, Ada/SPARK proofs, Idris, F*, Dafny,....

[Darmani]

Interesting. But when I search `"roadmap 2026" rust`, I only get results for the video game.

Am familiar with Linear Haskell (and actually went on a walk through Tokyo with one of the authors just a few months ago). IIRC: still no resources allocated to add the things that would actually make it useful. Had not been aware of most of those, except the dependently-typed ones. Cool to know about the others. Yay linear types becoming known.

You seem interesting, and I'm curious about your background now. All I can find so far is that you're from Europe and used to lead C++ in some major corporation.

[pjmlp]

I wish, I got the luck to do some C++ at CERN and Nokia Networks, but nothing out of the ordinary.

Just happen to be a nerd with interests across systems programming, languages, graphics, that rather reads books and papers than watching dull TV shows.

Day job is boring enterprise consulting across the usual stacks you might imagine.

Here is the roadmap.

https://rust-lang.github.io/rust-project-goals/2026/goals.ht...

[Darmani]

Sounds like a fun life :)

Have found in that roadmap things that would help me personally like making async functions dyn-compatible. Have not found the deeper stuff I thought you were hinting at.

Last year, I wanted to use the 5- line Result.flatten function, abs then found it had been stuck in experimental....for 5 years. That left me with no confidence of the language's dev velocity.

[sn9]

To disambiguate search results in the future, I've had great luck appending "lang" like so: "roadmap 2026 rust lang".

[adastra22]

(1) Higher order functions are pretty much the same as all the other languages you mentioned, using closure syntax? What was the problem you ran into?

(2) In such situations the compiler (type system or borrow checker) is telling you that what you wanted to do has hidden bugs, and therefore refuses to compile. Usually that's a good thing.

(3) &dyn Trait

[Darmani]

(1) Oh sure, the syntax is easy. Getting it to borrow-check is somewhere between insane and impossible. As I said, I've had friends who are actual Rust experts give up trying.

(2) No, it stems from a compiler limitation (imposed in large part by the need for static memory layout), not because there's anything intrinsically buggy about doing this.

(3) Look up "dyn-compatibility", for the largest, but not the only, problem with doing this.

[yobbo]

If your goal is to translate Haskell (or other garbage collected code) pattern-for-pattern into Rust, you will almost certainly burn out.

[Darmani]

It seems to be a common reflex of Rust advocates that, whenever an issue with using the language is asked about, the response is "That's just a garbage-collected code pattern" followed by "and therefore you shouldn't want it." It's happened multiple times in this thread. [Edit: and both the times I was thinking of were from you, so need to weaken that conclusion]

Aside from having vibes of "I've chosen to get hit weekly in the face with a baseball bat, but have learned to like it, and so should you" it's also seldom true.

All three of these examples are also quite easy to do with C and C++. It's not about garbage collection.

[Boxxed]

"It's possible to write <lang-X> in <lang-Y>" is a common trope, but "It's possible to write <lang-X> in Rust" is painful and borderline impossible in my experience. I don't mean this as a defense of rust, I just think it's why the learning curve is so harsh.

[adastra22]

Rust makes you be explicit about memory management. I guarantee you if you threw everything into a box inside an Arc, your copy closures would have still worked just fine and your Haskell idiom would translate cleanly. Only now everything is heap allocated and reference counted. Before LLMs took over the reins, this was the hallmark of beginner rust code because it WOULD work, just with unnecessary allocations and copying and pointer dereferencing.

Rust makes the tradeoffs explicit, and Rust programmers tend to obsess over minimizing those tradeoffs to get abstractions that are zero-cost. So doing it “the rust way” is often very complicated and tricky to get right while satisfying the borrow checker and type system, but once found is lean, fast, clean, and safe.

[Darmani]

Oy. It is also a common experience that, when I struggle in Rust to use a pattern that's common in nearly every other language or find another way to achieve the same goal, people who know of my Haskell background call it a "Haskell pattern," and thereby avoid facing the suggestion that their favorite language is missing some pretty basic affordances.

No, boxing everything does not magically make things more dyn-compatible. It will not magically solve the issue that tokio does a whole-program transformation that does its most restrictive checking only after all local checks have been resolved. It will not magically allow more reuse between datatypes. It will solve none of the problems I encountered... because if beginner-Rust could solve any of these problems, then they would have ceased to be problems for me by the time I became intermediate.

> Rust programmers tend to obsess over minimizing those tradeoffs to get abstractions that are zero-cost. So doing it “the rust way” is often very complicated and tricky to get right while satisfying the borrow checker and type system, but once found is lean, fast, clean, and safe.

You and I must be using very different definitions of "lean." For me, "complicated" and "lean" do not go together

[jvuygbbkuurx]

Maybe it depends on the application, but web servers are effortless with something like axum. Libraries can do a lot of heavy lifting to expose straightforward coding patterns. Never had any problems like you desribed with database connections and such. In rust with db pools things just work and get closed on drop etc. I would never even consider making a higher order function for that.

Only other language that I think gets close to rust ergonomics is Kotlin, but it suffers from having too many possibilities for abstractions.

[pjmlp]

Depends very much on the market.

On my line of work we don't do Web servers from scratch, we use lego pieces like with enterprise integrations.

Think Sitecore, Dynamics, Sharepoint, Optimizely, Contentful, SAP, Mongolia, Stripe, PayPal, Adobe, SQL Server, Oracle, DB2,.....

Axum offers very little over existing .NET, Java, nodejs SDKs provided by those vendors.

[dagi3d]

That's pretty interesting. I was thinking about starting a new pet project and was considering doing it in Rust to learn as I never tried anything with it and after some small pocs I had the feeling it was too verbose to my taste, but wasn't sure it was just me and/or my lack of experience with Rust. Still, wonder if it's still worth it to give a shot considering other positive elements of the language.

[jandrewrogers]

Verbosity aside, whether or not Rust is a good fit depends on what you are doing. The language design is broadly optimized for low-level application code, like command-line utilities. If that is the use case then you are likely to have a good experience.

For high-performance and high-reliability systems code, Rust is much more of a mixed bag. In a systems context it lacks the ability to easily and ergonomically express idiomatic constructs important for safety and performance that are trivial to express in e.g. C++. When you run into these cases it can get pretty ugly.

Most people don't write this kind of systems code. What most people call "systems code" is really more like low-level applications code, where Rust excels. It is software like highly-optimized kernel-bypass database engines and similar where the limitations start to show.

[mplanchard]

It’s worth learning, in my opinion, but I’ve been writing it professionally for the better part of a decade, so my opinion may be a bit skewed.

It’s my favorite language to write, and it gets much easier over time. As a first approximation, if you’re doing something and it feels insanely difficult like the GP is talking about, try to think of a different way to do it rather than fighting it. There’s usually a way to do almost anything, but it’s more pleasant to lean into the grooves the language pushes you towards.

[Darmani]

Rust is definitely very verbose. I think it's a fine choice -- probably even the best choice -- if you're doing systems code or if performance is your most important feature. If not, I would pass.

[tcfhgj]

> performance

or less ressource hungry software

[nothinkjustai]

Some say verbose, some say explicit. I had the complete opposite reaction to Rust than this other person, and I don’t think I’m particularly smart so I don’t think it’s purely a matter of intelligence. Even asynchronous rust is pretty easy once you get the hang of it.

[IshKebab]

That is a very unusual Rust experience. I find "application code" very pleasant to write in Rust. Of course there are things that aren't as ergonomic in Rust as in other languages (e.g. callbacks) but that's true of pretty much any language.

[Darmani]

I have heard this reaction from others before. One of the Rust expert friends I consulted with told me "I'm not convinced you're not trying to write Haskell-style code in Rust;" I told him the patterns I was struggling with were both trivial and common in Java.

The things I found quite difficult or impossible in Rust were to me pretty basic patterns for modularity and removing duplication that it's really shocking that these complaints are not more common.

I currently have but two hypotheses for why.

First, the second problem I mentioned only comes from using tokio, which causes your top-level program to secretly be using a defunctionalized continuation data type, derived from where exactly in other files you put your await's, that might not be Send. If you're not using tokio, you won't experience that issue.

Second...I was kinda told to just give up on deduplication and have lots of copy+pasted code. This raises the very uncomfortable hypothesis that Rust afficionados are some combination of people who came to Rust early and never learned traditional software design and don't know what they're missing, and people who were raised on traditional good software engineering but then got hit with Rust's metaphorical baseball bat of lack-of-modularity over and over until they got used to being hit with a baseball bat as a normal pain of life.

I don't like either of these explanations (esp. with tokio seeming quite dominant), so I'm awaiting an explanation that makes more sense. https://xkcd.com/3210/

[IshKebab]

> Rust afficionados are some combination of people who came to Rust early and never learned traditional software design and don't know what they're missing

This is definitely not the case and is unnecessarily insulting.

The truth is that some things are harder in Rust but a) often those things are best avoided anyway (e.g. callbacks), and b) it's worth the trade-off because of the other good things it allows.

Surely as a Haskell user of all things you must understand that sometimes making things harder is worth the trade-off. Yeay everything is pure! Great for many reasons. Now how do I add logging to this deeply nested function?

[Darmani]

> is unnecessarily insulting.

I know that it's insulting! And it doesn't make sense, because I generally think Rust programmers are smart people. But right now, it's the only explanation I've got, so it is alas necessarily insulting. So please, please, please give me a better explanation that actually makes sense.

> The truth is that some things are harder in Rust but a) often those things are best avoided anyway (e.g. callbacks), and b) it's worth the trade-off because of the other good things it allows.

This sounds like the seeds of a better explanation, but it needs a lot more to actually suffice. E.g.: why are callbacks best avoided anyway, when they're virtually required for a large number of important programming patterns? (In more technical language: they're effectively the only way to eliminate duplication in non-leaf-expressions. In even more technical language: they're the way to do second-order anti-unification.)

> Surely as a Haskell user of all things you must understand that sometimes making things harder is worth the trade-off. Yeay everything is pure! Great for many reasons. Now how do I add logging to this deeply nested function?

And this is a great illustration of the difference. First, you will seldom find Haskell programmers trying to argue that, actually, things like deeply-nested logging that everyone wants are actually "best avoided anyway." Second, you'll actually get a solution if you ask about them -- in this case, to either use MTL-style, to use a fixed alias for your monad stack, or that unsafePerformIO isn't actually that bad.

BTW, similar to my unpleasant conclusion for Rust above, I have another unpleasant conclusion for Haskell: Haskell is incredible for medium-sized programs, but it has its own missing modularity features that make it non-ideal for large programs (e.g.: >50k lines). But this is a much smaller problem than it sounds because Haskell is so compact that, while many projects can be huge, very few individual codebases will need to approach that size.

[IshKebab]

> why are callbacks best avoided anyway

Look up "callback hell". Basically they encourage spaghetti.

> you'll actually get a solution if you ask about them

You got solutions to your problems didn't you? Macros are a perfectly reasonable thing to use in Rust, even if they are best avoided where possible. Exactly like unsafePerformIO.

If you were expecting Rust to work perfectly in every situation... well it doesn't. GUI programming in particular is still awkward, and async Rust has more footguns than anyone is happy with.

Despite that it's still probably the best language we have for a surprisingly large range of domains.

[Darmani]

> Look up "callback hell". Basically they encourage spaghetti.

Ah. I think you're confusing the general idea of a callback with one particular style of use. "callback hell" refers to the deep indentation that occurs when trying to program in monadic style in languages without syntactic support for monads. It was mostly solved by adding async/await syntax, aka syntactic support for the continuation monad. "Callback hell" is not spaghetti in any deep sense, merely syntactically cumbersome.

But a "callback" is a more general term, sometimes a synonym for "function parameter," sometimes for more narrow kinds of function parameter (e.g.: void function, invokable once). Many people will refer to the function argument of the `map` function as a callback, but no-one would refer to that as "callback hell."

Callbacks are quite universal, and most uses do not lead at all to callback hell. I've engaged with this topic a little bit at https://us16.campaign-archive.com/?u=8b565c97b838125f69e75fb... , above the header "Serious Business."

> You got solutions to your problems didn't you?

Mostly no :(

And when I did, I largely got it by figuring stuff out myself, while being told by multiple Rust experts that I either shouldn't care about the verbosity and lack of modularity, or that if I have a problem like "using the interface instead of the implementation" it must be because I'm a Haskeller.

Well, my ultimate solution was to start working on a new product, and to not use any Rust, except for some performance-heavy libraries. With the first product, the market had changed too much by the time we were ready for prime-time, and I'd put somewhere between 25% and 70% of the reason for that delay on our choice to start building new parts of the backend in Rust.

> Macros are a perfectly reasonable thing to use in Rust, even if they are best avoided where possible. Exactly like unsafePerformIO.

Good comparison!

> Despite that it's still probably the best language we have for a surprisingly large range of domains.

I agree with this. I just don't agree that that list of domains has a very large intersection with the set of applications.

[yobbo]

> difficult or impossible in Rust were to me pretty basic patterns for modularity

Many things are plainly not permitted, either because the borrow-checker isn't clever enough, or the pattern is unsafe (without garbage collection and so on).

Many functional/Haskell patterns simply can not be translated directly to Rust.

[Darmani]

That "and so on" is doing a lot of work. You may accept rejecting garbage collection as a reasonable trade-off, but the bulk of the cost is coming from a much more aggressive tradeoff Rust is making with is at odds with the goals of most application code.

A deeply-baked assumption of Rust is that your memory layout is static. Dynamic memory layout is perfectly compatible with manual memory management, but Rust does not readily support it because of its demands for static memory layout.

A very easy place to see this is the difference in decorator types between Rust and other languages like Java. Java's legacy File/reader API has you write things like `new PrintWriter(new BufferedWriter(new FileWriter("foo.txt")))`, where each layer adds some functionality to the base layer. The resulting value has principal type `PrintWriter` and can be used through the `Writer` interface.

The equivalent code in Rust would give you a value of type `PrintWriter<BufferedWriter<FileWriter>>` which can only be passed to functions that expect exactly that type and not, say, a `PrintWriter<BufferedWriter<StringStream>>`. You would solve this by using a template function that takes a `T where T: Writer` parameter and gets compiled separately for every use-site, thus contributing to Rust's infamous slow build times.

It would be perfectly sane, and desirable for application code, to be able to pass around a PrintWriter value as an owned pointer to a PrintWriter struct which contains an owned pointer to a BufferedWriter struct which contains an owned pointer to a FileWriter struct. You could even have each pointer actually be to a Writer value of unknown size, and thus recover modularity.

In Rust, there is sometimes a painful and very fragile way to do this: have each writer type contain a Box<&dyn Writer>, effectively the same as the Java solution above. This works, except that, if one day you want to add a method to the Writer trait that breaks dyn-compatibility, then you will no longer be able to do this, and will need to rewrite all code that uses this type.

[mplanchard]

You can usually manage dyn compatibility issues in my experience by writing a base trait that is not dyn compatible and then an Ext trait that is, which is auto implemented for all implementers of the base trait. You see this pattern all over the place, including with several of the buffer traits you mentioned.

Mostly, this works out well enough: dyn compatibility pretty much just insists your methods can in fact work with just a reference to an unknown variant of the type.

[Darmani]

Good suggestion. I think started doing that kind of thing towards the end of my days with Rust. It's been close to a year now, and don't remember how well it worked out.

[germandiago]

Some people ask me why I do not use Rust as opposed to C++ if it is already safer and more modern.

But I see the forums (and I also trued some toy stuff at times) plagued with rigidity problems that in C++ have obvious solutions.

For example, I am not going to fight a borrow-checker all the stack up to get a 0.0005% perf improvement, if sny, when I can use smart pointers.

I am not going to use Result everywhere when I can throw an exception and get done with it instead of refactoring all the stack up for the intermediate return types (though I use expected and optional and like them, but it is a choice depending on what I am doing).

I am not going to elaborate safe interfaces for my arrays of data I need to send to a GPU: there is no vslue in it and I can get it wrong snyway, it os ceremony. I assume this kind of code is unsafe by nature.

I find C++ just more flexible. Yes, it has warts, but I use all warnings as errors, clang tidy and have a lot of flexibility. I use values to avoid any trace of dangling and when it is going to get bad, I can, most of the time, switch to smart pointers.

I really do not get why someone would use Rust except for very niche cases like absolutely no memory unsafety (but this is not free either, as some reports show: you need to really be careful about reviewing unsafe if your domain is unsafe by nature or uses bindings to keep Rust invariants or you write only safe code, in whcih case, if memory safety is critical, it does give you something).

But I do not see Rust good for writing general application code. At least not compared to well-written C++ nowadays.

[singpolyma3]

I have to sit with the specific example, but a PrintWriter struct which owns a Box<impl Writer> and has no generics should be quite doable I'd think?

[Darmani]

*`dyn Writer`. `impl Writer` can only be used in function parameters.

This was one of the example approaches I gave. This works...at first. The problem is that, if you want to add a new function to the Writer trait which makes Writer no longer dyn-compatible, such as, say, any async function, then you can no longer write `Box<dyn Writer>` and need to rewrite all code that uses it.

(although you can dig under the hood and specify a pinned-down Future type, covering one kind of awfulness with another)

[singpolyma3]

Arc + clone or even just clone gets you 95% of the way to GC, no?

[mplanchard]

The most confusing thing that can happen with something like tokio is the failure-at-distance you can get from writing a non-Send future somewhere in the depths of a call stack and then having to figure out why your top-level spawn isn’t working. There’s a non-default lint I highly recommend turning on when working with tokio: clippy::future_not_send. Forces all your futures to be Send, unless you opt out, which really helps keep the reasoning local when you run into errors.

FWIW I write primarily rust, and I do not agree with the advice given in your second point, so I’d take it with a grain of salt were I you.

[Darmani]

Thanks! Very helpful. Pain is still there, but surfaced early.

[nothinkjustai]

> Rust afficionados are some combination of people who came to Rust early and never learned traditional software design and don't know what they're missing, and people who were raised on traditional good software engineering but then got hit with Rust's metaphorical baseball bat of lack-of-modularity over and over until they got used to being hit with a baseball bat as a normal pain of life.

Oh please. I came to Rust late, after using plenty of other languages. I have never had a problem with “modularity”. You express surprise that these issues haven’t been talked about more, well the null hypothesis is that you are just not very good at Rust and it hasn’t clicked for you - that’s fine, I doubt I would be very good at Haskell. But don’t insult us, and don’t assume your experience is de facto everyone’s and we’re just in denial. It’s incredibly arrogant.

[Darmani]

I respect that your experience is different.

Please respect the fact that I do not understand how one can like Rust without giving up caring about modularity.

I have pretty good reason for thinking this is a possibility. Directly, because the Rust experts I asked for help did in fact advocate giving up modularity. Indirectly, in that I've seen something similar but much stronger in a different language. That culminated in a conversation with several of the creators of that language, in which they argued their language was great for generic programming...while revealing some pretty basic holes in their understanding of generic programming (while calling me a "Haskell weenie," among other abuse). I am very confident in my conclusion about this other language community and not interested in getting into the details of this event. I am just sharing where I'm coming from, in not immediately dismissing this idea as too absurd to consider even when I have no other hypothesis.

I acknowledge that you feel personally insulted by me having a hypothesis that requires a large group of people behave in ways I consider strange. I have evidence for that hypothesis, and have been unable to find a better one. I hope you can see how the comment I am responding to crosses an extra line and is directly personally insulting.

I would very much like to come away from this discussion no longer believing that Rust programminh is at odds with modularity. I have shared some fairly basic and detailed criticisms, the ones I still remember after a year out of the language. Perhaps your can play a role in offering solutions to them -- or admit that these are indeed problems your hadn't noticed before or had gotten used to