Result and ? in Rust

Recoverable errors, and the ? early-return operator.

fn parse_sum(a: &str, b: &str) -> Result<i32, std::num::ParseIntError> {
    let x: i32 = a.parse()?;
    let y: i32 = b.parse()?;
    Ok(x + y)
}

fn main() {
    match parse_sum("3", "4") {
        Ok(total) => println!("sum: {total}"),
        Err(e) => println!("error: {e}"),
    }
}

How it works

1. parse()? returns early on an error.
2. The function's error type is the parse error.
3. match handles Ok and Err at the call site.

Keywords and builtins used here

• Err
• Ok
• Result
• fn
• i32
• let
• main
• match
• parse_sum
• str

The run, in numbers

Lines

12

Characters to type

252

Tokens

101

Three-star pace

100 tpm

At the three-star pace of 100 tokens a minute, this run takes about 61 seconds.

Type this snippet

Step 1 of 4 in Result & the ? operator, step 4 of 15 in Error handling.

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