Errors when running quickstart from docs

[bertday]

What version of regex are you using?

1.10.4

Describe the bug at a high level.

When I run the quick example from the landing page of the regex docs, I get two errors.

What are the steps to reproduce the behavior?

First, cargo add regex to a new project. Then, run the example from the docs. (I can't link to it directly, so I'll copy it below.)

use regex::Regex;

let re = Regex::new(r"(?m)^([^:]+):([0-9]+):(.+)$").unwrap();
let hay = "\
path/to/foo:54:Blue Harvest
path/to/bar:90:Something, Something, Something, Dark Side
path/to/baz:3:It's a Trap!
";

let mut results = vec![];
for (_, [path, lineno, line]) in re.captures_iter(hay).map(|c| c.extract()) {
    results.push((path, lineno.parse::<u64>()?, line));
}
assert_eq!(results, vec![
    ("path/to/foo", 54, "Blue Harvest"),
    ("path/to/bar", 90, "Something, Something, Something, Dark Side"),
    ("path/to/baz", 3, "It's a Trap!"),
]);

What is the actual behavior?

I get an error:

error[E0277]: the `?` operator can only be used in a function that returns `Result` or `Option` (or another type that implements `FromResidual`)
  --> src/main.rs:25:50
   |
3  | fn main() {
   | --------- this function should return `Result` or `Option` to accept `?`
...
25 |         results.push((path, lineno.parse::<u64>()?, line));
   |                                                  ^ cannot use the `?` operator in a function that returns `()`
   |
   = help: the trait `FromResidual<Result<Infallible, ParseIntError>>` is not implemented for `()`

If I change lineno.parse::<u64>()? to lineno.parse::<u64>().unwrap() the error goes away, but then I run into a different error:

thread 'main' panicked at src/main.rs:27:5:
assertion `left == right` failed
  left: [("path/to/foo", 54, "Blue Harvest"), ("        path/to/bar", 90, "Something, Something, Something, Dark Side"), ("        path/to/baz", 3, "It's a Trap!")]
 right: [("path/to/foo", 54, "Blue Harvest"), ("path/to/bar", 90, "Something, Something, Something, Dark Side"), ("path/to/baz", 3, "It's a Trap!")]
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

What is the expected behavior?

I expect the example to work without errors. I'm new to Rust so I may just be missing something, but I think my expectation is that I can essentially copy/paste the example from the docs and it should work.

Thank you for any insights on this!

[BurntSushi]

The error tells you the problem. Your function should return a Result. The main function can do that.

I think I can add the main function to the example to avoid this specific speed bump. But doc examples generally have to assume some base background knowledge of Rust.

[bertday]

Thank you for explaining that @BurntSushi! There's definitely a lot I'm still absorbing about Rust :)

I think having the quickstart example be self-contained in a main function would be helpful for newcomers like me, but understand if it's not a Rust doc norm.