Crate error_rules

Intro

Key feature of the error-rules is chained error handling.

Idea is simple, each module has own error handler. Source error wrapped into error handler with configurable display text.

Declaring error types

Macro error_rules! implements Error, Result types and all necessary traits for Error. All arguments should be comma-separated.

To prevent types shadowing all errors from standard library and other crates should be used with module name. For example: io::Error.

Display format

Error display text defines in tuple after Error => keyword. First tuple argument is a format string. Additional arguments:

• error - chained error text

use error_rules::*;

error_rules! {
    Error => ("app error => {}", error)
}

assert_eq!(
    Error::from("error message").to_string().as_str(),
    "app error => error message");

Error types

After display text you could define error types for conversions into Error chain. By the default implements conversion for: &str, String

use std::io;
use error_rules::*;

error_rules! {
    Error => ("app error => {}", error),
    std::io::Error,
}

let io_error = io::Error::new(io::ErrorKind::Other, "io-error");
assert_eq!(
    Error::from(io_error).to_string().as_str(),
    "app error => io-error");

Custom error types

Custom errors is an additional error kind to use with Error. Defines like struct with display arguments after => keyword. Could be defined without fields:

error_rules! {
    Error => ("app error => {}", error),
    CustomError => ("custom error"),
}

assert_eq!(
    Error::from(CustomError).to_string().as_str(),
    "app error => custom error");

or with fields:

error_rules! {
    Error => ("app error => {}", error),
    CustomError(usize) => ("custom error value:{}", 0),
}

assert_eq!(
    Error::from(CustomError(100)).to_string().as_str(),
    "app error => custom error value:100");

or with named fields:

error_rules! {
    Error => ("app error => {}", error),
    CustomError {
        value: usize,
    } => ("custom error value:{}", value),
}

assert_eq!(
    Error::from(CustomError { value: 100 }).to_string().as_str(),
    "app error => custom error value:100");

Macros

bail	Exits a function and returns Error
ensure	Ensure that a boolean expression is true at runtime. If condition is false then invokes bail! macro
error_rules	Macro for chained error handling