I found this funny.

The context is as explained by @laund@hachyderm.io

the issue is that you can't return from inside a closure, since the closure might be called later/elsewhere

and this post was the asnwer to the question by @antonok@fosstodon.org

you got me curious what the record for the longest ? operator chain on crates.io is

Original post: https://fosstodon.org/users/antonok/statuses/111134824451525448

  • KillTheMule@programming.dev
    ·
    9 months ago

    While funny, this also highlights part of why I like rust's error handling story so much: You can really just read the happy path and understand what's going on. The error handling takes up minimal space, yet with one glance you can see that errors are all handled (bubbled up in this case). The usual caveats still apply, of course ;)

    • 1984@lemmy.today
      ·
      9 months ago

      I'm writing my Rust wrong... I have match statements everywhere to the degree that it's cluttering up everything.

      • Aloso@programming.dev
        ·
        9 months ago

        If all you do in the Err(e) => ... match arm is returning the error, then you absolutely should use the ? operator instead.

        If the match arm also converts the error type into another error type, implement the From trait for the conversion, then you can use ? as well.

        If you want to add more information to the error, you can use .map_err(...)?. Or, if you're using the anyhow crate, .with_context(...)?.

  • BB_C@programming.dev
    ·
    9 months ago

    Is everyone genuinely liking this!

    This is, IMHO, not a good style.

    Isn't something like this much clearer?

    // Add `as_cstr()` to `NixPath` trait first

let some_or_null_cstr = |v| v.map(NixPath::as_cstr)
  .unwrap_or(Ok(std::ptr::null()));

// `Option::or_null_cstr()` for `OptionᐸTᐳ`
// where `T:  NixPath` would make this even better
let source_cstr = some_or_null_cstr(＆source)?;
let target_cstr = target.as_cstr()?;
let fs_type_cstr = some_or_null_cstr(＆fs_type)?;
let data_cstr = some_or_null_cstr(＆data)?;
let res = unsafe { .. };

    Edit: using alternative chars to circumvent broken Lemmy sanitization.

    • realharo@lemm.ee
      ·
      9 months ago

      I think the issue with this is that the code (https://docs.rs/nix/0.27.1/src/nix/lib.rs.html#297) allocates a fixed-size buffer on the stack in order to add a terminating zero to the end of the path copied into it. So it just gives you a reference into that buffer, which can't outlive the function call.

      They do also have a with_nix_path_allocating function (https://docs.rs/nix/0.27.1/src/nix/lib.rs.html#332) that just gives you a CString that owns its buffer on the heap, so there must be some reason why they went this design. Maybe premature optimization? Maybe it actually makes a difference? 🤔

      They could have just returned the buffer via some wrapper that owns it and has the as_cstr function on it, but that would have resulted in a copy, so I'm not sure if it would have still achieved what they are trying to achieve here. I wonder if they ran some benchmarks on all this stuff, or they're just writing what they think will be fast.

  • sip@programming.dev
    ·
    9 months ago

    there was a comment about adding an ?! operator that would resolve any number of ? operators but I can't find it.

    • Aloso@programming.dev
      ·
      9 months ago

      I can't remember ever needing more than two question marks (??), and even that is very rare in my experience.