made in gimp, with <3

Context for actual rust programmers

I 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<dyn Error> 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;
    }
}
  • [object Object]@sh.itjust.worksEnglish
    762·
    1 month ago

    Rust output is bad? I feel like it’s one of the best in terms of telling you where you got things wrong. Nix output when you accidentally get infinite recursion is so bad.

    Come to think of it, Nix fits all three better than Rust.

  • anyhow2503@lemmy.world
    621·
    1 month ago

    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?

    • communism@lemmy.ml
      111·
      1 month ago

      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…?

        • anyhow2503@lemmy.world
          3·
          1 month 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.

  • wisha@lemmy.ml
    12·
    1 month 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 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;
    }
}