Error Handling

TL;DR

• No exceptions. Use Result<T, E> for recoverable, panic! for unrecoverable.
• ? operator propagates errors up the call chain.
• Use thiserror for library errors, anyhow for application errors.

The Basics

use std::fs;

// Returns Result — caller decides what to do
fn read_config(path: &str) -> Result<String, std::io::Error> {
    fs::read_to_string(path)
}

// ? propagates error to caller
fn get_port() -> Result<u16, Box<dyn std::error::Error>> {
    let config = fs::read_to_string("config.toml")?;
    let port: u16 = config.trim().parse()?;
    Ok(port)
}

Cheat Sheet

Custom Errors (thiserror)

use thiserror::Error;

#[derive(Error, Debug)]
enum AppError {
    #[error("not found: {0}")]
    NotFound(String),
    #[error("io error")]
    Io(#[from] std::io::Error),
    #[error("parse error")]
    Parse(#[from] std::num::ParseIntError),
}