this post was submitted on 18 Apr 2026
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made in gimp, with <3

Context for actual rust programmersI was having massive beef with the rust compiler yesterday, every cargo check takes 20 seconds.

And then look at the three functions below, only one of them are Send, if you know why, please let me know.

(Note: value that is not Send cannot be held across an await point, and Box is not Send)

async fn one() {
    let res: Result<(), Box<dyn Error>> = do_stuff();
    if let Err(err) = res {
        let content = err.to_string();
        let _ = do_stuff(content).await;
    }
}

async fn two() {
    let res: Result<(), Box<dyn Error>> = do_stuff();
    let content = if let Err(err) = res {
        Some(err.to_string())
    } else {
        None
    };
    drop(res);
    if let Some(content) = content {
        let _ = do_stuff(content).await;
    }
}

async fn three() {
    let content = {
        let res: Result<(), Box<dyn Error>> = do_stuff();
        if let Err(err) = res {
            Some(err.to_string())
        } else {
            None
        }
    };
    if let Some(content) = content {
        let _ = do_stuff(content).await;
    }
}

all 45 comments
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[–] anyhow2503@lemmy.world 69 points 4 weeks ago (3 children)

I get that it's supposed to be a meme, but aside from the first one these aren't even rust stereotypes. Is this a meme specifically for people who haven't used rust, know nothing about rust but have maybe heard that it's a programming language?

[–] nightlily@leminal.space 23 points 4 weeks ago (1 children)

Yeah, part of the point of Rust is that it does exactly what you tell it - sometimes to the point of absurdity. No implicit casting for instance.

[–] MoffKalast@lemmy.world 7 points 3 weeks ago* (last edited 3 weeks ago)

And here I was thinking most of our programming problems come from the thing doing exactly what we told it to, but didn't quite think the process through enough. Or at all.

[–] Fontasia@feddit.nl 13 points 4 weeks ago (2 children)

This is for people who learnt C++ in 2008 and refuse to believe that they've never fucked up a malloc in their lives

[–] Liketearsinrain@lemmy.ml 6 points 3 weeks ago* (last edited 3 weeks ago)

C++

malloc

You aren't supposed to use malloc in C++ with very few exceptions.

[–] limer@lemmy.ml 1 points 3 weeks ago

Hah I learned c++ in the 90s and never felt shame for messing up an allocation.

I think when this happens, I have a puddle of memory, the spilled ram “lubricates” the pointers, which often rub against each other. The wasted memory acts like oil does to a rusted chain. It’s helping push the program through the finish line.

Yes, I am having fun here

[–] communism@lemmy.ml 8 points 4 weeks ago (1 children)

I mean Rust is definitely known for long compilation times but yeah otherwise I am not sure how any of this is Rust-specific. Maybe by "doesn't do what you tell it to do" they mean the borrow checker and strict compile time checks...?

[–] siriusmart@lemmy.world 8 points 4 weeks ago (1 children)

i've edited the post content for context, and a small puzzle for rust programmers

[–] anyhow2503@lemmy.world 3 points 3 weeks ago

I was actually wondering if this was supposed to be about a specific problem someone has with rust (not like I haven't gotten stuck on some weird corner with rust before), but looking at the meme, that seemed unlikely to me. Thanks for the context.

[–] BlueKey@fedia.io 54 points 4 weeks ago (2 children)

output makes no sense

C++ template errors enter the room

[–] SpaceNoodle@lemmy.world 14 points 4 weeks ago (1 children)

Template errors make sense as long as you carefully read the entire error, but nobody has ever actually done that.

[–] marcos@lemmy.world 21 points 4 weeks ago (1 children)

You are saying that the error messages terminate at some point?

[–] SpaceNoodle@lemmy.world 12 points 4 weeks ago (1 children)

Well, yeah, templates won't recurse beyond 1,024 levels.

[–] mkwt@lemmy.world 1 points 3 weeks ago (1 children)

That's an implementation-defined behaviour.

[–] SpaceNoodle@lemmy.world 1 points 3 weeks ago

I like to pretend that gcc is the only compiler

[–] Courantdair@jlai.lu 5 points 4 weeks ago

boost::msm errors enter the room

[–] Ooops@feddit.org 35 points 4 weeks ago

So a narrow but clear win for the Rust compiler still...

[–] kibiz0r@midwest.social 31 points 4 weeks ago (1 children)
[–] leo85811nardo@lemmy.world 13 points 4 weeks ago

Deterministic when hit by that weird cosmic ray: ❌❌

/jk

[–] Courantdair@jlai.lu 27 points 4 weeks ago
cargo() {
  cargo $@
  echo So how you doin\' today?
}

Fixed

[–] Prunebutt@slrpnk.net 23 points 4 weeks ago (3 children)

I thought the rust compiler was supposed to be polite and helpful (unlike gcc, or nix).

[–] Sibbo@sopuli.xyz 44 points 4 weeks ago

It is, this meme is just trash.

[–] SpaceNoodle@lemmy.world 5 points 4 weeks ago (1 children)

gcc was unhelpful a couple decades ago. I've found it to be rather helpful in recent years.

[–] verdare@piefed.blahaj.zone 6 points 4 weeks ago (1 children)

Yeah, recent versions of GCC have gotten a lot better. I suspect it’s actually because of languages like Rust raising the bar.

[–] SpaceNoodle@lemmy.world 0 points 4 weeks ago (1 children)
[–] WhyJiffie@sh.itjust.works 3 points 3 weeks ago (1 children)
[–] SpaceNoodle@lemmy.world 1 points 3 weeks ago (2 children)

They literally did. They theorized that Rust influenced GCC's improved error messaging. That could not have happened if GCC improved their error messaging prior to the existence of Rust.

[–] fruitcantfly@programming.dev 6 points 3 weeks ago (1 children)

But GCC did not improve their error messages (much) prior to Rust, despite Clang's error messages comparing favorably to GCC even before Rust 1.0 was released, as for example discussed in

https://gcc.gnu.org/wiki/ClangDiagnosticsComparison?action=recall&rev=1

Rust itself is 14 years old, slightly older than above wiki page, and even back then it had great error messages, though they've also improved since. Here's a fun site where you can see how error messages have evolved through Rust's life:

https://kobzol.github.io/rust/rustc/2025/05/16/evolution-of-rustc-errors.html

It's only very recently that GCC has started to catch up, for example with some nice improvements in GCC 15:

https://developers.redhat.com/articles/2025/04/10/6-usability-improvements-gcc-15

[–] SpaceNoodle@lemmy.world 3 points 3 weeks ago

Oh, guess my mental timeline is wrong!

[–] WhyJiffie@sh.itjust.works 0 points 3 weeks ago (1 children)

no they didn't, yes it could have happened:

  1. GCC: exists, not too good messages
  2. rust gets made
  3. rust gets popular
  4. gcc error messages get improved by good example of rust

gcc is not a dead project. it is continuously maintained. its improvements can be influenced by other projects like rust

[–] SpaceNoodle@lemmy.world 0 points 3 weeks ago

I know that gcc is still alive. That was implied from my original comment.

What you just outlined is the other commenter's theory I already outlined, and literally describes Rust not coming along after gcc improves its error messaging. Thus, it contradicts my theory that Rust came along later than gcc's improved error messaging.

[–] kibiz0r@midwest.social 4 points 4 weeks ago (1 children)
[–] Prunebutt@slrpnk.net 6 points 4 weeks ago

You create a new file and don't check it into git yet.

Nix commands: "I've never met this file in my life!"

[–] kubica@fedia.io 21 points 4 weeks ago

cargo delete this_post

[–] wisha@lemmy.ml 15 points 3 weeks ago

You are running into the Send Approximation being too conservative. The compiler does not like to see a let binding for a non-Send type and an .await statement in the same scope. It is not (yet) smart enough to know that the non-Send type is already be consumed by the time of the .await.

You've already discovered the workaround in your three(). To make it more concise

async fn four() {
    let content = do_stuff().err().map(|err| err.to_string());
    if let Some(content) = content {
        let _ = do_stuff_2(content).await;
    }
}
[–] PlexSheep@infosec.pub 8 points 3 weeks ago

This is an awful "meme"

[–] cadekat@pawb.social 8 points 3 weeks ago (1 children)

Just a guess, but are you missing + Send on your error type?

[–] Ephera@lemmy.ml 5 points 3 weeks ago

Yeah, I was gonna say, that might be the root cause.

In the vast majority of cases, you want Box<dyn Error + Send + Sync>, but folks tend to leave out the Send + Sync, because it looks like additional complexity to them, and because it doesn't cause problems when they're not doing async/await.
It's better to define a type alias, if you don't want that long type name everywhere.

[–] Grail@multiverse.soulism.net 6 points 3 weeks ago

I love the rust compiler, it makes debugging so easy

[–] Cevilia@lemmy.blahaj.zone 4 points 4 weeks ago

sometimes?! Cargo never makes sense to me!

[–] Noja@sopuli.xyz 2 points 3 weeks ago

First mistake was using async

[–] psud@aussie.zone 1 points 3 weeks ago (2 children)

https://xkcd.com/303/ vs this guy who thinks 20 seconds is a long time

[–] mkwt@lemmy.world 2 points 3 weeks ago

I've done professional work on an old Unix system where the full build was more than 2 hours, and an incremental stop-rebuild-restart cycle was 20 minutes.

You get to where you really stare at your edits for a while before you hit build.

[–] Kolanaki@pawb.social 1 points 3 weeks ago

"This could take like a hundred milliseconds. It could even take gasp ONE WHOLE SECOND! 😱"