Reacting per error kind in Rust

Matching on an error's variant so each failure gets its own recovery.

use std::num::IntErrorKind;

fn classify(text: &str) -> &'static str {
    match text.parse::<u8>() {
        Ok(_) => "fits in a byte",
        Err(e) => match e.kind() {
            IntErrorKind::Empty => "empty input",
            IntErrorKind::InvalidDigit => "not a number",
            IntErrorKind::PosOverflow => "too large",
            _ => "unusable",
        },
    }
}

fn main() {
    for text in ["7", "", "abc", "9000"] {
        println!("{text:?}: {}", classify(text));
    }
    println!("{}", matches!("5".parse::<u8>(), Ok(n) if n > 3));
}

How it works

1. kind() on an IO error names the category.
2. Matching lets one branch retry and another give up.
3. matches! is the terse form when you only need a bool.

Keywords and builtins used here

• Err
• Ok
• classify
• fn
• for
• if
• in
• main
• match
• static
• str
• u8
• use

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105 tpm

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Step 2 of 2 in Panics & recovery, step 14 of 15 in Error handling.

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