491 lines
14 KiB
Rust
491 lines
14 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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//! Traits for working with Errors.
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//!
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//! # The `Error` trait
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//!
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//! `Error` is a trait representing the basic expectations for error values,
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//! i.e. values of type `E` in `Result<T, E>`. At a minimum, errors must provide
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//! a description, but they may optionally provide additional detail (via
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//! `Display`) and cause chain information:
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//!
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//! ```
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//! use std::fmt::Display;
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//!
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//! trait Error: Display {
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//! fn description(&self) -> &str;
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//!
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//! fn cause(&self) -> Option<&Error> { None }
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//! }
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//! ```
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//!
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//! The `cause` method is generally used when errors cross "abstraction
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//! boundaries", i.e. when a one module must report an error that is "caused"
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//! by an error from a lower-level module. This setup makes it possible for the
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//! high-level module to provide its own errors that do not commit to any
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//! particular implementation, but also reveal some of its implementation for
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//! debugging via `cause` chains.
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#![stable(feature = "rust1", since = "1.0.0")]
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// A note about crates and the facade:
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//
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// Originally, the `Error` trait was defined in libcore, and the impls
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// were scattered about. However, coherence objected to this
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// arrangement, because to create the blanket impls for `Box` required
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// knowing that `&str: !Error`, and we have no means to deal with that
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// sort of conflict just now. Therefore, for the time being, we have
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// moved the `Error` trait into libstd. As we evolve a sol'n to the
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// coherence challenge (e.g., specialization, neg impls, etc) we can
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// reconsider what crate these items belong in.
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use any::TypeId;
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use cell;
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use char;
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use fmt::{self, Debug, Display};
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use marker::Reflect;
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use mem::transmute;
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use num;
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use str;
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use string;
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/// Base functionality for all errors in Rust.
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#[stable(feature = "rust1", since = "1.0.0")]
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pub trait Error: Debug + Display + Reflect {
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/// A short description of the error.
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///
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/// The description should not contain newlines or sentence-ending
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/// punctuation, to facilitate embedding in larger user-facing
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/// strings.
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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///
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/// match "xc".parse::<u32>() {
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/// Err(e) => {
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/// println!("Error: {}", e.description());
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/// }
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/// _ => println!("No error"),
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/// }
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn description(&self) -> &str;
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/// The lower-level cause of this error, if any.
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///
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/// # Examples
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///
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/// ```
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/// use std::error::Error;
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/// use std::fmt;
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///
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/// #[derive(Debug)]
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/// struct SuperError {
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/// side: SuperErrorSideKick,
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/// }
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///
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/// impl fmt::Display for SuperError {
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/// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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/// write!(f, "SuperError is here!")
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/// }
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/// }
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///
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/// impl Error for SuperError {
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/// fn description(&self) -> &str {
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/// "I'm the superhero of errors!"
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/// }
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///
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/// fn cause(&self) -> Option<&Error> {
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/// Some(&self.side)
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/// }
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/// }
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///
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/// #[derive(Debug)]
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/// struct SuperErrorSideKick;
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///
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/// impl fmt::Display for SuperErrorSideKick {
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/// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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/// write!(f, "SuperErrorSideKick is here!")
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/// }
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/// }
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///
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/// impl Error for SuperErrorSideKick {
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/// fn description(&self) -> &str {
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/// "I'm SuperError side kick!"
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/// }
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/// }
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///
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/// fn get_super_error() -> Result<(), SuperError> {
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/// Err(SuperError { side: SuperErrorSideKick })
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/// }
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///
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/// fn main() {
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/// match get_super_error() {
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/// Err(e) => {
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/// println!("Error: {}", e.description());
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/// println!("Caused by: {}", e.cause().unwrap());
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/// }
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/// _ => println!("No error"),
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/// }
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/// }
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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fn cause(&self) -> Option<&Error> { None }
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/// Get the `TypeId` of `self`
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#[doc(hidden)]
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#[unstable(feature = "error_type_id",
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reason = "unclear whether to commit to this public implementation detail",
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issue = "27745")]
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fn type_id(&self) -> TypeId where Self: 'static {
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TypeId::of::<Self>()
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, E: Error + 'a> From<E> for Box<Error + 'a> {
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fn from(err: E) -> Box<Error + 'a> {
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Box::new(err)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<Error + Send + Sync + 'a> {
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fn from(err: E) -> Box<Error + Send + Sync + 'a> {
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Box::new(err)
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl From<String> for Box<Error + Send + Sync> {
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fn from(err: String) -> Box<Error + Send + Sync> {
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#[derive(Debug)]
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struct StringError(String);
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impl Error for StringError {
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fn description(&self) -> &str { &self.0 }
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}
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impl Display for StringError {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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Display::fmt(&self.0, f)
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}
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}
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Box::new(StringError(err))
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}
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}
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#[stable(feature = "string_box_error", since = "1.7.0")]
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impl From<String> for Box<Error> {
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fn from(str_err: String) -> Box<Error> {
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let err1: Box<Error + Send + Sync> = From::from(str_err);
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let err2: Box<Error> = err1;
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err2
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<'a, 'b> From<&'b str> for Box<Error + Send + Sync + 'a> {
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fn from(err: &'b str) -> Box<Error + Send + Sync + 'a> {
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From::from(String::from(err))
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}
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}
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#[stable(feature = "string_box_error", since = "1.7.0")]
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impl<'a> From<&'a str> for Box<Error> {
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fn from(err: &'a str) -> Box<Error> {
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From::from(String::from(err))
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Error for str::ParseBoolError {
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fn description(&self) -> &str { "failed to parse bool" }
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Error for str::Utf8Error {
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fn description(&self) -> &str {
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"invalid utf-8: corrupt contents"
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Error for num::ParseIntError {
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fn description(&self) -> &str {
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self.__description()
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}
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}
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#[unstable(feature = "try_from", issue = "33417")]
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impl Error for num::TryFromIntError {
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fn description(&self) -> &str {
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self.__description()
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Error for num::ParseFloatError {
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fn description(&self) -> &str {
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self.__description()
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Error for string::FromUtf8Error {
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fn description(&self) -> &str {
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"invalid utf-8"
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}
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl Error for string::FromUtf16Error {
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fn description(&self) -> &str {
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"invalid utf-16"
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}
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}
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#[stable(feature = "str_parse_error2", since = "1.8.0")]
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impl Error for string::ParseError {
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fn description(&self) -> &str {
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match *self {}
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}
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}
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#[stable(feature = "decode_utf16", since = "1.9.0")]
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impl Error for char::DecodeUtf16Error {
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fn description(&self) -> &str {
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"unpaired surrogate found"
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}
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}
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#[stable(feature = "box_error", since = "1.7.0")]
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impl<T: Error> Error for Box<T> {
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fn description(&self) -> &str {
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Error::description(&**self)
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}
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fn cause(&self) -> Option<&Error> {
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Error::cause(&**self)
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}
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}
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#[stable(feature = "fmt_error", since = "1.11.0")]
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impl Error for fmt::Error {
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fn description(&self) -> &str {
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"an error occurred when formatting an argument"
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}
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}
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#[unstable(feature = "try_borrow", issue = "35070")]
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impl<'a, T: ?Sized + Reflect> Error for cell::BorrowError<'a, T> {
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fn description(&self) -> &str {
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"already mutably borrowed"
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}
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}
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#[unstable(feature = "try_borrow", issue = "35070")]
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impl<'a, T: ?Sized + Reflect> Error for cell::BorrowMutError<'a, T> {
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fn description(&self) -> &str {
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"already borrowed"
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}
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}
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#[unstable(feature = "try_from", issue = "33417")]
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impl Error for char::CharTryFromError {
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fn description(&self) -> &str {
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"converted integer out of range for `char`"
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}
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}
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// copied from any.rs
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impl Error + 'static {
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/// Returns true if the boxed type is the same as `T`
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn is<T: Error + 'static>(&self) -> bool {
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// Get TypeId of the type this function is instantiated with
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let t = TypeId::of::<T>();
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// Get TypeId of the type in the trait object
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let boxed = self.type_id();
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// Compare both TypeIds on equality
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t == boxed
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}
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/// Returns some reference to the boxed value if it is of type `T`, or
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/// `None` if it isn't.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
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if self.is::<T>() {
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unsafe {
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Some(&*(self as *const Error as *const T))
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}
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} else {
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None
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}
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}
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/// Returns some mutable reference to the boxed value if it is of type `T`, or
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/// `None` if it isn't.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
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if self.is::<T>() {
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unsafe {
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Some(&mut *(self as *mut Error as *mut T))
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}
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} else {
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None
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}
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}
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}
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impl Error + 'static + Send {
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/// Forwards to the method defined on the type `Any`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn is<T: Error + 'static>(&self) -> bool {
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<Error + 'static>::is::<T>(self)
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}
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/// Forwards to the method defined on the type `Any`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
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<Error + 'static>::downcast_ref::<T>(self)
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}
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/// Forwards to the method defined on the type `Any`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
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<Error + 'static>::downcast_mut::<T>(self)
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}
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}
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impl Error + 'static + Send + Sync {
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/// Forwards to the method defined on the type `Any`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn is<T: Error + 'static>(&self) -> bool {
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<Error + 'static>::is::<T>(self)
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}
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/// Forwards to the method defined on the type `Any`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_ref<T: Error + 'static>(&self) -> Option<&T> {
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<Error + 'static>::downcast_ref::<T>(self)
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}
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/// Forwards to the method defined on the type `Any`.
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#[stable(feature = "error_downcast", since = "1.3.0")]
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#[inline]
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pub fn downcast_mut<T: Error + 'static>(&mut self) -> Option<&mut T> {
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<Error + 'static>::downcast_mut::<T>(self)
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}
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}
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impl Error {
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#[inline]
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#[stable(feature = "error_downcast", since = "1.3.0")]
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/// Attempt to downcast the box to a concrete type.
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pub fn downcast<T: Error + 'static>(self: Box<Self>) -> Result<Box<T>, Box<Error>> {
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if self.is::<T>() {
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unsafe {
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let raw: *mut Error = Box::into_raw(self);
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Ok(Box::from_raw(raw as *mut T))
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}
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} else {
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Err(self)
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}
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}
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}
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impl Error + Send {
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#[inline]
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#[stable(feature = "error_downcast", since = "1.3.0")]
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/// Attempt to downcast the box to a concrete type.
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pub fn downcast<T: Error + 'static>(self: Box<Self>)
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-> Result<Box<T>, Box<Error + Send>> {
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let err: Box<Error> = self;
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<Error>::downcast(err).map_err(|s| unsafe {
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// reapply the Send marker
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transmute::<Box<Error>, Box<Error + Send>>(s)
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})
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}
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}
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impl Error + Send + Sync {
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#[inline]
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#[stable(feature = "error_downcast", since = "1.3.0")]
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/// Attempt to downcast the box to a concrete type.
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pub fn downcast<T: Error + 'static>(self: Box<Self>)
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-> Result<Box<T>, Box<Self>> {
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let err: Box<Error> = self;
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<Error>::downcast(err).map_err(|s| unsafe {
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// reapply the Send+Sync marker
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transmute::<Box<Error>, Box<Error + Send + Sync>>(s)
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})
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}
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}
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#[cfg(test)]
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mod tests {
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use super::Error;
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use fmt;
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#[derive(Debug, PartialEq)]
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struct A;
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#[derive(Debug, PartialEq)]
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struct B;
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impl fmt::Display for A {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "A")
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}
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}
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impl fmt::Display for B {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(f, "B")
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}
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}
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impl Error for A {
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fn description(&self) -> &str { "A-desc" }
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}
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impl Error for B {
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fn description(&self) -> &str { "A-desc" }
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}
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#[test]
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fn downcasting() {
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let mut a = A;
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let mut a = &mut a as &mut (Error + 'static);
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assert_eq!(a.downcast_ref::<A>(), Some(&A));
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assert_eq!(a.downcast_ref::<B>(), None);
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assert_eq!(a.downcast_mut::<A>(), Some(&mut A));
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assert_eq!(a.downcast_mut::<B>(), None);
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let a: Box<Error> = Box::new(A);
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match a.downcast::<B>() {
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Ok(..) => panic!("expected error"),
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Err(e) => assert_eq!(*e.downcast::<A>().unwrap(), A),
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}
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}
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}
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