exowos/subject_text/errors/result.md

name = "Results" file = "src/errors/result.rs"

name = "Results" file = "src/errors/result.rs"

We saw earlier the Option type, which represents a possibly absent value (sometimes called "nullable" in other languages). Now it would be useful to carry the reason of this absence of value. Let's say you are parsing an integer from a String, there are multiple ways it can fail.

• The string contains invalid characters (non-digits).
• The value we want to parse is too large (for example, trying to parse "999999999999" as an i32).

If we want to react properly, we need to know why it failed. So instead of having only None as output, we would like a variant like SomeError(v). In Rust, this type with Some and SomeError variants is called Result.

Its variants are Ok and Err, and we can use it much like Option:

// creating values of type Result
let itworked: Result<i32, &str> = Ok(420);
let oops: Result<i32, &str> = Err("badb002e");

// using values from Result
match itworked {
    Ok(value) => println!("yes, we got {value}"),
    Err(err) => eprintln!("oh no, some error occured: {err}"),
}

/// Returns `true` if the result contains an `Err`
pub fn is_err(res: &Result<i32, &str>) -> bool {
    unimplemented!()
}

/// Returns `true` if the result contains a `Ok`
pub fn is_ok(res: &Result<i32, &str>) -> bool {
    unimplemented!()
}

/// Returns the wrapped `&str` if any, panic otherwise
pub fn get_err_or_panic(res: Result<i32, &str>) -> &str {
    unimplemented!()
}

/// Returns the wrapped `i32` if any, panic otherwise
pub fn get_val_or_panic(res: Result<i32, &str>) -> i32 {
    unimplemented!()
}

/// Transforms `Ok` to `Some` and `Err` to `None`
/// effectively discarding the `Err` wrapped value
pub fn discard_err(res: Result<i32, &str>) -> Option<i32> {
    unimplemented!()
}

fn main() {
    dbg!(is_err(Ok(10))); // false
    dbg!(is_ok(Ok(128))); // true
    dbg!(get_err_or_panic(Err("oh no"))); // "oh no"
    dbg!(get_val_or_panic(Ok(420))); // 420
    dbg!(discard_err(Ok(69))); // Some(69)
}