Return an inline-defined enum from a function? - enums

Question

I'm diving into rust, and I'm trying to do something like this:
match send("select * from User;") {
ConnError => println!("Connection error!"),
DBError(e) => println!("Database error {}", e),
Ok(response) => {
...
}
}
and I'm trying to figure out a compact way of defining the send function. I saw the Result enum, but it only handles one kind of error at a time. I was hoping that I could define my own enum like this:
fn send(query: str) -> enum { Ok(Box<Response>), ConnError, DBError(str) } {
...
}
alas, it is not possible, it's complaining about the unexpected 'enum' keyword. Is there any way to do what I'm trying here, or perhaps make Result handle multiple error types? Thanks!

Answer 1

As you say, you can use Result but you have to define the enum with your error types separately, as you can't define it directly in the return of your function.
Something like this:
use std::rand::distributions::{IndependentSample, Range};
fn main() {
match send("select * from foo") {
Ok(Response) => println!("response"),
Err(e) => match e {
ConnError => println!("connection error"),
DbError(err) => println!("{}", err)
}
}
}
// the enum with your errors
enum DataLayerError {
ConnError,
DbError(String)
}
struct Response; /*...*/
fn send(_query: &str) -> Result<Response, DataLayerError> {
let between = Range::new(0u, 2);
let mut rng = std::rand::task_rng();
// return a random result
match between.ind_sample(&mut rng) {
0 => Ok(Response),
1 => Err(DbError("yikes".to_string())),
2 => Err(ConnError),
_ => unreachable!()
}
}