Crate easyerr

easyerr

crate for easier creation and transformation of error types. heavily inspired by thiserror and snafu, which are way more mature. go check them out!

goals

• small library (< 1k LOC)
• easy to use
• doesn’t show up in your public API

basic usage

(completely made up example - i’m not very creative so take this with a grain of salt)

use easyerr::prelude::*;
use std::path::PathBuf;

#[derive(Debug, Error)]
enum ValidateMessageError {
    #[error("message is too short: {f0} bytes")]
    TooShort(usize),
    #[error("message is too long: {f0} bytes")]
    TooLong(usize),
}

fn validate_message(msg: &str) -> Result<(), ValidateMessageError> {
    ensure!(msg.len() < 20, ValidateMessageError::TooShort(msg.len()));
    ensure!(msg.len() > 100, ValidateMessageError::TooLong(msg.len()));

    Ok(())
}

#[derive(Debug, Error)]
enum OpenMyStructError {
    #[error("failed to read message from {path:?}")]
    Read {
        source: std::io::Error,
        path: PathBuf,
    },
    #[error(transparent)] // delegates display and .source() to `source`
    Validation { source: ValidateMessageError },
}

struct MyStruct {
    magic_number: u32,
    message: String,
}

impl MyStruct {
    fn open_my_struct(path: PathBuf) -> Result<Self, OpenMyStructError> {
        let message = std::fs::read_to_string(&path).context(OpenMyStructCtx::Read { path })?;
        validate_message(&message).context(OpenMyStructCtx::Validation)?;

        Ok(Self {
            magic_number: 42,
            message,
        })
    }
}

the example does not show it, but structs are supported too!

Modules

prelude

Prelude. Currently, just reexports everything (a grand total of… 4 items), but might change in the future.

Macros

ensure

Macro that evaluates an expression and returns an error if it is not true.

Traits

ErrorContext

Trait for types which can add context to some Error (Source), transforming it into a new Error (Err).

ResultExt

Extension trait for Result which adds useful methods to use ErrorContexts.

Derive Macros

Error