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// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Traits for working with Errors.
//!
//! # The `Error` trait
//!
//! `Error` is a trait representing the basic expectations for error values,
//! i.e. values of type `E` in `Result<T, E>`. At a minimum, errors must provide
//! a description, but they may optionally provide additional detail (via
//! `Display`) and cause chain information:
//!
//! ```
//! use std::fmt::Display;
//!
//! trait Error: Display {
//! fn description(&self) -> &str;
//!
//! fn cause(&self) -> Option<&Error> { None }
//! }
//! ```
//!
//! The `cause` method is generally used when errors cross "abstraction
//! boundaries", i.e. when a one module must report an error that is "caused"
//! by an error from a lower-level module. This setup makes it possible for the
//! high-level module to provide its own errors that do not commit to any
//! particular implementation, but also reveal some of its implementation for
//! debugging via `cause` chains.
#![stable(feature = "rust1", since = "1.0.0")]
use prelude::*;
use fmt::{Debug, Display};
/// Base functionality for all errors in Rust.
#[stable(feature = "rust1", since = "1.0.0")]
pub trait Error: Debug + Display {
/// A short description of the error.
///
/// The description should not contain newlines or sentence-ending
/// punctuation, to facilitate embedding in larger user-facing
/// strings.
#[stable(feature = "rust1", since = "1.0.0")]
fn description(&self) -> &str;
/// The lower-level cause of this error, if any.
#[stable(feature = "rust1", since = "1.0.0")]
fn cause(&self) -> Option<&Error> { None }
}
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