How do I implement an external trait for an external struct?

[dimitarvp]

Yep, worked. Thanks for reminding me that I didn't pay enough attention before. I am getting a bit overloaded but definitely not stopping!

I am much more ahead now. Currently grappling with how to serialize a rustler::error::Error to a normal Rust Error.

[alice]

Huh, the rustler::Error error type apparently doesn't implement the Error trait from std. Maybe it's for errors that are meant to be returned to erlang instead of to Rust?

[dimitarvp]

It could be. I noticed several Rustler examples where people directly use the ? operator (which means it'll just transparently return Err(whatever)).

[dimitarvp]

I am still not getting the whole "translate one error to another" thing correctly.

Here's a snippet from a sample project from Rustler's author:

fn io_error_to_term<'a>(env: Env<'a>, err: &IoError) -> Term<'a> {
    let error = match err.kind() {
        IoErrorKind::NotFound => atoms::enoent().encode(env),
        IoErrorKind::PermissionDenied => atoms::eacces().encode(env),
        IoErrorKind::BrokenPipe => atoms::epipe().encode(env),
        IoErrorKind::AlreadyExists => atoms::eexist().encode(env),
        _ => format!("{}", err).encode(env),
    };

    (atoms::error(), error).encode(env)
}

macro_rules! handle_io_error {
    ($env:expr, $e:expr) => {
        match $e {
            Ok(inner) => inner,
            Err(ref error) => return Ok(io_error_to_term($env, error)),
        }
    };
}

Earlier, you also alluded to writing my own function to map between those different errors.

Still looking how to do the translation.

---

EDIT: @alice I hit a new user posting limit. Here's what I tried to reply to your comment below:

I got a bit disoriented. In this particular case I have to pattern-match on all 4 enum variants of rustler::Error and just return Erlang string or atom depending.

My mistake, apologies.

[alice]

What are you missing? The posted snippet seems rather complete for conversion from IO error to rustler term.

[dimitarvp]

Thanks in part to intense back-and-forth session with @OvermindDL1 who, besides providing a PR, also provided a lot of extra explanations on top of what @alice did, the initial phase of the project is now a success:

Link to the file with the exact commit.

Thanks so much to the amazing community.

[dimitarvp]

@OvermindDL1's PR that pointed me in the right direction: Get the rust code compiling by OvermindDL1 · Pull Request #4 · dimitarvp/xqlite · GitHub