errors3.rs has outdated informations

[rusty-snake]

rustlings/exercises/error_handling/errors3.rs

Lines 48 to 58 in 5e1d7c3

	// Since the `?` operator returns an `Err` early if the thing it's trying to
	// do fails, you can only use the `?` operator in functions that have a
	// `Result` as their return type.
	// Hence the error that you get if you run this code is:
	// ```
	// error[E0277]: the `?` operator can only be used in a function that returns `Result` (or another type that implements `std::ops::Try`)
	// ```
	// So we have to use another way of handling a `Result` within `main`.

Since rust 1.26 main can also return Result.

[mikemorris]

I was just working through this exercise and noticed this too, the following is now a acceptable solution solution that compiles for example

fn main() -> Result<String, ParseIntError> {
    let mut tokens = 100;
    let pretend_user_input = "8";

    let cost = total_cost(pretend_user_input)?;

    if cost > tokens {
        Ok(format!("You can't afford that many!"))
    } else {
        tokens -= cost;
        Ok(format!("You now have {} tokens.", tokens))
    }
}

[rusty-snake]

maybe better:fn main() -> Result<(), AnyErrorType>

because fn main() -> String isn't allowed.

[EvanCarroll]

I'm not sure that this issue should be marked as completed. Previously the lesson was that you can use ? only if you're returning a result, but if you want to panic on error and only concern yourself with success you can use the .unwrap().

let cost = total_cost(pretend_user_input)?; # old
let cost = total_cost(pretend_user_input).unwrap(); #fixed

The hint says,

If other functions can return a `Result`, why shouldn't `main`?

That's pushing the users to make main return a Result. The user is likely to look up "how do I make main return a result".