simple-error

simple-error is a Rust library that provides a simple Error type backed by a String. It is best used when all you care about the error is an error string.

Documentation

Usage

To use simple-error, first add this to your Cargo.toml:

[dependencies]
simple-error = "0.3"

Then import what you use (Rust 2018/2021):

use simple_error::{SimpleError, try_with};
// Add others as needed: require_with, ensure_with, bail, simple_error, map_err_with

Now you can use simple-error in different ways:

You can use it simply as a string error type:

fn do_foo() -> Result<(), SimpleError> {
    Err(SimpleError::new("cannot do foo"))
}

You can use it to replace all error types if you only care about a string description:

fn do_bar() -> Result<(), SimpleError> {
    Err(SimpleError::from(std::io::Error::new(std::io::ErrorKind::Other, "oh no")))
}

Or you can chain all the errors, and get a complete error description at the top level:

fn find_tv_remote() -> Result<(), SimpleError> {
    try_with!(std::fs::File::open("remotefile"), "failed to open remote file");
    Ok(())
}

fn turn_on_tv() -> Result<(), std::io::Error> {
    Ok(())
}

fn watch_tv() -> Result<(), SimpleError> {
    try_with!(find_tv_remote(), "tv remote not found");
    try_with!(turn_on_tv(), "cannot turn on tv");
    Ok(())
}

fn study() -> Result<(), SimpleError> {
    Ok(())
}

fn run() -> Result<(), SimpleError> {
    try_with!(study(), "cannot study");
    try_with!(watch_tv(), "cannot watch tv");
    Ok(())
}

fn main() {
    if let Err(e) = run() {
        println!("{}", e);
    }
}
// This prints out "cannot watch tv, tv remote not found, failed to open remote file, Text file busy" if the error is text file busy.

You can also ensure a condition holds and early-return a SimpleError if it does not:

use simple_error::{SimpleError, ensure_with};

fn check_config(is_valid: bool) -> Result<(), SimpleError> {
    ensure_with!(is_valid, "invalid config");
    Ok(())
}

Macros

• try_with! — unwrap Result, else return SimpleError::with.
• require_with! — unwrap Option, else return SimpleError::new.
• ensure_with! — assert boolean, else return SimpleError::new.
• bail! — return early with a SimpleError (supports format/expr).
• simple_error! — construct a SimpleError (supports format/expr).
• map_err_with! — map a Result’s error with extra context.