thiserror
The thiserror
crate provides macros to help avoid boilerplate when defining error types. It provides derive macros that assist in implementing From<T>
, Display
, and the Error
trait.
use std::io::Read; use std::{fs, io}; use thiserror::Error; #[derive(Debug, Error)] enum ReadUsernameError { #[error("I/O error: {0}")] IoError(#[from] io::Error), #[error("Found no username in {0}")] EmptyUsername(String), } fn read_username(path: &str) -> Result<String, ReadUsernameError> { let mut username = String::with_capacity(100); fs::File::open(path)?.read_to_string(&mut username)?; if username.is_empty() { return Err(ReadUsernameError::EmptyUsername(String::from(path))); } Ok(username) } fn main() { //fs::write("config.dat", "").unwrap(); match read_username("config.dat") { Ok(username) => println!("Username: {username}"), Err(err) => println!("Error: {err:?}"), } }
This slide should take about 5 minutes.
- The
Error
derive macro is provided bythiserror
, and has lots of useful attributes to help define error types in a compact way. - The message from
#[error]
is used to derive theDisplay
trait. - Note that the (
thiserror::
)Error
derive macro, while it has the effect of implementing the (std::error::
)Error
trait, is not the same this; traits and macros do not share a namespace.