Crate disperror

disperror

Displaying errors instead of Debugging them when returned from main.

Usage

Simply wrap your error type MyError in a DispError:

- fn main() -> Result<(), MyError> {
+ use disperror::DispError;
+ fn main() -> Result<(), DispError<MyError>> {

Note that MyError must implement std::error::Error.

Example

use disperror::DispError;

fn main() -> Result<(), DispError<std::io::Error>> {
    let contents = std::fs::read_to_string("nonexistent_file.txt")?;
    println!("{}", contents);
    Ok(())
}

Should Display the following error message if that file does not exist:

Error: No such file or directory (os error 2)

Instead of the usual Debug output:

Error: Os { code: 2, kind: NotFound, message: "No such file or directory" }

Implementation

The DispError type is a simple wrapper around an error type E that implements std::error::Error:

use std::error::Error;

pub struct DispError<E: Error>(E);

The Debug implementation of DispError forwards to the Display implementation of the inner error:

use std::{error::Error, fmt::Debug};

impl<E: Error> Debug for DispError<E> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

In addition, DispError implements From<E> for implicit conversion:

impl<E: Error> From<E> for DispError<E> {
    fn from(error: E) -> Self {
        Self(error)
    }
}

In this way, when an error of type E is returned from main, it is automatically converted to a DispError<E>. When the Err variant of a Result is returned from main, the Debug implementation is used to print the error message, thus forwarding to the Display implementation of the inner error.

Notes

This project is heavily inspired by main_error. If you’re working with Box<dyn std::error::Error> in your main function, use main_error instead. Here’s a quick comparison:

	disperror	main_error
Library size	Tiny	Small
Overhead	None	Negligible
Dynamic dispatch	✘	✔
Usage	DispError<E>	MainError

Structs

DispError

A wrapper for errors implementing std::error::Error, that when Debugged, will Display the contained error. Usually used in the signature of a main function - see examples in the crate documentation.