<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source to the Rust file `libstd/error.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>error.rs.html -- source</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc source"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><a href='../../std/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span>
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</pre><pre class="rust ">
<span class="comment">// Copyright 2014 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="doccomment">//! Traits for working with Errors.</span>
<span class="attribute">#![<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="comment">// A note about crates and the facade:</span>
<span class="comment">//</span>
<span class="comment">// Originally, the `Error` trait was defined in libcore, and the impls</span>
<span class="comment">// were scattered about. However, coherence objected to this</span>
<span class="comment">// arrangement, because to create the blanket impls for `Box` required</span>
<span class="comment">// knowing that `&str: !Error`, and we have no means to deal with that</span>
<span class="comment">// sort of conflict just now. Therefore, for the time being, we have</span>
<span class="comment">// moved the `Error` trait into libstd. As we evolve a sol'n to the</span>
<span class="comment">// coherence challenge (e.g., specialization, neg impls, etc) we can</span>
<span class="comment">// reconsider what crate these items belong in.</span>
<span class="kw">use</span> <span class="ident">alloc</span>::{<span class="ident">AllocErr</span>, <span class="ident">LayoutErr</span>, <span class="ident">CannotReallocInPlace</span>};
<span class="kw">use</span> <span class="ident">any</span>::<span class="ident">TypeId</span>;
<span class="kw">use</span> <span class="ident">borrow</span>::<span class="ident">Cow</span>;
<span class="kw">use</span> <span class="ident">cell</span>;
<span class="kw">use</span> <span class="ident">char</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">array</span>;
<span class="kw">use</span> <span class="ident">fmt</span>::{<span class="self">self</span>, <span class="ident">Debug</span>, <span class="ident">Display</span>};
<span class="kw">use</span> <span class="ident">mem</span>::<span class="ident">transmute</span>;
<span class="kw">use</span> <span class="ident">num</span>;
<span class="kw">use</span> <span class="ident">str</span>;
<span class="kw">use</span> <span class="ident">string</span>;
<span class="doccomment">/// `Error` is a trait representing the basic expectations for error values,</span>
<span class="doccomment">/// i.e. values of type `E` in [`Result<T, E>`]. Errors must describe</span>
<span class="doccomment">/// themselves through the [`Display`] and [`Debug`] traits, and may provide</span>
<span class="doccomment">/// cause chain information:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The [`cause`] method is generally used when errors cross "abstraction</span>
<span class="doccomment">/// boundaries", i.e. when a one module must report an error that is "caused"</span>
<span class="doccomment">/// by an error from a lower-level module. This setup makes it possible for the</span>
<span class="doccomment">/// high-level module to provide its own errors that do not commit to any</span>
<span class="doccomment">/// particular implementation, but also reveal some of its implementation for</span>
<span class="doccomment">/// debugging via [`cause`] chains.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Result<T, E>`]: ../result/enum.Result.html</span>
<span class="doccomment">/// [`Display`]: ../fmt/trait.Display.html</span>
<span class="doccomment">/// [`cause`]: trait.Error.html#method.cause</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">trait</span> <span class="ident">Error</span>: <span class="ident">Debug</span> <span class="op">+</span> <span class="ident">Display</span> {
<span class="doccomment">/// **This method is soft-deprecated.**</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Although using it won’t cause compilation warning,</span>
<span class="doccomment">/// new code should use [`Display`] instead</span>
<span class="doccomment">/// and new `impl`s can omit it.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// To obtain error description as a string, use `to_string()`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`Display`]: ../fmt/trait.Display.html</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// match "xc".parse::<u32>() {</span>
<span class="doccomment">/// Err(e) => {</span>
<span class="doccomment">/// // Print `e` itself, not `e.description()`.</span>
<span class="doccomment">/// println!("Error: {}", e);</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// _ => println!("No error"),</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"description() is deprecated; use Display"</span>
}
<span class="doccomment">/// The lower-level cause of this error, if any.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Examples</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">/// use std::error::Error;</span>
<span class="doccomment">/// use std::fmt;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// #[derive(Debug)]</span>
<span class="doccomment">/// struct SuperError {</span>
<span class="doccomment">/// side: SuperErrorSideKick,</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// impl fmt::Display for SuperError {</span>
<span class="doccomment">/// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {</span>
<span class="doccomment">/// write!(f, "SuperError is here!")</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// impl Error for SuperError {</span>
<span class="doccomment">/// fn description(&self) -> &str {</span>
<span class="doccomment">/// "I'm the superhero of errors"</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn cause(&self) -> Option<&Error> {</span>
<span class="doccomment">/// Some(&self.side)</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// #[derive(Debug)]</span>
<span class="doccomment">/// struct SuperErrorSideKick;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// impl fmt::Display for SuperErrorSideKick {</span>
<span class="doccomment">/// fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {</span>
<span class="doccomment">/// write!(f, "SuperErrorSideKick is here!")</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// impl Error for SuperErrorSideKick {</span>
<span class="doccomment">/// fn description(&self) -> &str {</span>
<span class="doccomment">/// "I'm SuperError side kick"</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn get_super_error() -> Result<(), SuperError> {</span>
<span class="doccomment">/// Err(SuperError { side: SuperErrorSideKick })</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn main() {</span>
<span class="doccomment">/// match get_super_error() {</span>
<span class="doccomment">/// Err(e) => {</span>
<span class="doccomment">/// println!("Error: {}", e.description());</span>
<span class="doccomment">/// println!("Caused by: {}", e.cause().unwrap());</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// _ => println!("No error"),</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">fn</span> <span class="ident">cause</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Error</span><span class="op">></span> { <span class="prelude-val">None</span> }
<span class="doccomment">/// Get the `TypeId` of `self`</span>
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">hidden</span>)]</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_type_id"</span>,
<span class="ident">reason</span> <span class="op">=</span> <span class="string">"unclear whether to commit to this public implementation detail"</span>,
<span class="ident">issue</span> <span class="op">=</span> <span class="string">"27745"</span>)]</span>
<span class="kw">fn</span> <span class="ident">type_id</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">TypeId</span> <span class="kw">where</span> <span class="self">Self</span>: <span class="lifetime">'static</span> {
<span class="ident">TypeId</span>::<span class="ident">of</span>::<span class="op"><</span><span class="self">Self</span><span class="op">></span>()
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">E</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">E</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">err</span>: <span class="ident">E</span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">err</span>)
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">E</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">E</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">err</span>: <span class="ident">E</span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">err</span>)
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">From</span><span class="op"><</span><span class="ident">String</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">err</span>: <span class="ident">String</span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span><span class="op">></span> {
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">struct</span> <span class="ident">StringError</span>(<span class="ident">String</span>);
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">StringError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> { <span class="kw-2">&</span><span class="self">self</span>.<span class="number">0</span> }
}
<span class="kw">impl</span> <span class="ident">Display</span> <span class="kw">for</span> <span class="ident">StringError</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="ident">Display</span>::<span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="number">0</span>, <span class="ident">f</span>)
}
}
<span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">StringError</span>(<span class="ident">err</span>))
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"string_box_error"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.6.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">From</span><span class="op"><</span><span class="ident">String</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">str_err</span>: <span class="ident">String</span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">err1</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span><span class="op">></span> <span class="op">=</span> <span class="ident">From</span>::<span class="ident">from</span>(<span class="ident">str_err</span>);
<span class="kw">let</span> <span class="ident">err2</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> <span class="op">=</span> <span class="ident">err1</span>;
<span class="ident">err2</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="lifetime">'b</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'b</span> <span class="ident">str</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">err</span>: <span class="kw-2">&</span><span class="lifetime">'b</span> <span class="ident">str</span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">From</span>::<span class="ident">from</span>(<span class="ident">String</span>::<span class="ident">from</span>(<span class="ident">err</span>))
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"string_box_error"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.6.0"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span><span class="op">></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">err</span>: <span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">str</span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> {
<span class="ident">From</span>::<span class="ident">from</span>(<span class="ident">String</span>::<span class="ident">from</span>(<span class="ident">err</span>))
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cow_box_error"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.22.0"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="lifetime">'b</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">Cow</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">str</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">err</span>: <span class="ident">Cow</span><span class="op"><</span><span class="lifetime">'b</span>, <span class="ident">str</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> <span class="op">+</span> <span class="lifetime">'a</span><span class="op">></span> {
<span class="ident">From</span>::<span class="ident">from</span>(<span class="ident">String</span>::<span class="ident">from</span>(<span class="ident">err</span>))
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"cow_box_error"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.22.0"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> <span class="ident">From</span><span class="op"><</span><span class="ident">Cow</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">str</span><span class="op">>></span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">err</span>: <span class="ident">Cow</span><span class="op"><</span><span class="lifetime">'a</span>, <span class="ident">str</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> {
<span class="ident">From</span>::<span class="ident">from</span>(<span class="ident">String</span>::<span class="ident">from</span>(<span class="ident">err</span>))
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"never_type"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"35121"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="op">!</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> { <span class="kw-2">*</span><span class="self">self</span> }
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>,
<span class="ident">reason</span> <span class="op">=</span> <span class="string">"the precise API and guarantees it provides may be tweaked."</span>,
<span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">AllocErr</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"memory allocation failed"</span>
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>,
<span class="ident">reason</span> <span class="op">=</span> <span class="string">"the precise API and guarantees it provides may be tweaked."</span>,
<span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">LayoutErr</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"invalid parameters to Layout::from_size_align"</span>
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>,
<span class="ident">reason</span> <span class="op">=</span> <span class="string">"the precise API and guarantees it provides may be tweaked."</span>,
<span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">CannotReallocInPlace</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="ident">CannotReallocInPlace</span>::<span class="ident">description</span>(<span class="self">self</span>)
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">str</span>::<span class="ident">ParseBoolError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> { <span class="string">"failed to parse bool"</span> }
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">str</span>::<span class="ident">Utf8Error</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"invalid utf-8: corrupt contents"</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">num</span>::<span class="ident">ParseIntError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="self">self</span>.<span class="ident">__description</span>()
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_from"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"33417"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">num</span>::<span class="ident">TryFromIntError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="self">self</span>.<span class="ident">__description</span>()
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_from"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"33417"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">array</span>::<span class="ident">TryFromSliceError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="self">self</span>.<span class="ident">__description</span>()
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">num</span>::<span class="ident">ParseFloatError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="self">self</span>.<span class="ident">__description</span>()
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">string</span>::<span class="ident">FromUtf8Error</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"invalid utf-8"</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"rust1"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.0.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">string</span>::<span class="ident">FromUtf16Error</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"invalid utf-16"</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"str_parse_error2"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.8.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">string</span>::<span class="ident">ParseError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="kw">match</span> <span class="kw-2">*</span><span class="self">self</span> {}
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"decode_utf16"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.9.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">char</span>::<span class="ident">DecodeUtf16Error</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"unpaired surrogate found"</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"box_error"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.8.0"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span><span class="op">></span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">Box</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="ident">Error</span>::<span class="ident">description</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="self">self</span>)
}
<span class="kw">fn</span> <span class="ident">cause</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">Error</span><span class="op">></span> {
<span class="ident">Error</span>::<span class="ident">cause</span>(<span class="kw-2">&</span><span class="kw-2">*</span><span class="kw-2">*</span><span class="self">self</span>)
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"fmt_error"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.11.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">fmt</span>::<span class="ident">Error</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"an error occurred when formatting an argument"</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">cell</span>::<span class="ident">BorrowError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"already mutably borrowed"</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_borrow"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.13.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">cell</span>::<span class="ident">BorrowMutError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"already borrowed"</span>
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_from"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"33417"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">char</span>::<span class="ident">CharTryFromError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"converted integer out of range for `char`"</span>
}
}
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"char_from_str"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.20.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">char</span>::<span class="ident">ParseCharError</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="self">self</span>.<span class="ident">__description</span>()
}
}
<span class="comment">// copied from any.rs</span>
<span class="kw">impl</span> <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span> {
<span class="doccomment">/// Returns true if the boxed type is the same as `T`</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="comment">// Get TypeId of the type this function is instantiated with</span>
<span class="kw">let</span> <span class="ident">t</span> <span class="op">=</span> <span class="ident">TypeId</span>::<span class="ident">of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>();
<span class="comment">// Get TypeId of the type in the trait object</span>
<span class="kw">let</span> <span class="ident">boxed</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">type_id</span>();
<span class="comment">// Compare both TypeIds on equality</span>
<span class="ident">t</span> <span class="op">==</span> <span class="ident">boxed</span>
}
<span class="doccomment">/// Returns some reference to the boxed value if it is of type `T`, or</span>
<span class="doccomment">/// `None` if it isn't.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_ref</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">is</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() {
<span class="kw">unsafe</span> {
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">*</span>(<span class="self">self</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">Error</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">T</span>))
}
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
<span class="doccomment">/// Returns some mutable reference to the boxed value if it is of type `T`, or</span>
<span class="doccomment">/// `None` if it isn't.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_mut</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span><span class="op">></span> {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">is</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() {
<span class="kw">unsafe</span> {
<span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="kw-2">*</span>(<span class="self">self</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Error</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>))
}
} <span class="kw">else</span> {
<span class="prelude-val">None</span>
}
}
}
<span class="kw">impl</span> <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span> <span class="op">+</span> <span class="ident">Send</span> {
<span class="doccomment">/// Forwards to the method defined on the type `Any`.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>::<span class="ident">is</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="self">self</span>)
}
<span class="doccomment">/// Forwards to the method defined on the type `Any`.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_ref</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">T</span><span class="op">></span> {
<span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>::<span class="ident">downcast_ref</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="self">self</span>)
}
<span class="doccomment">/// Forwards to the method defined on the type `Any`.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_mut</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span><span class="op">></span> {
<span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>::<span class="ident">downcast_mut</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="self">self</span>)
}
}
<span class="kw">impl</span> <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> {
<span class="doccomment">/// Forwards to the method defined on the type `Any`.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">is</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">bool</span> {
<span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>::<span class="ident">is</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="self">self</span>)
}
<span class="doccomment">/// Forwards to the method defined on the type `Any`.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_ref</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="ident">T</span><span class="op">></span> {
<span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>::<span class="ident">downcast_ref</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="self">self</span>)
}
<span class="doccomment">/// Forwards to the method defined on the type `Any`.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast_mut</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">T</span><span class="op">></span> {
<span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>::<span class="ident">downcast_mut</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="self">self</span>)
}
}
<span class="kw">impl</span> <span class="ident">Error</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="doccomment">/// Attempt to downcast the box to a concrete type.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="self">self</span>: <span class="ident">Box</span><span class="op"><</span><span class="self">Self</span><span class="op">></span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">>></span> {
<span class="kw">if</span> <span class="self">self</span>.<span class="ident">is</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>() {
<span class="kw">unsafe</span> {
<span class="kw">let</span> <span class="ident">raw</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">Error</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="self">self</span>);
<span class="prelude-val">Ok</span>(<span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">raw</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>))
}
} <span class="kw">else</span> {
<span class="prelude-val">Err</span>(<span class="self">self</span>)
}
}
}
<span class="kw">impl</span> <span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="doccomment">/// Attempt to downcast the box to a concrete type.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="self">self</span>: <span class="ident">Box</span><span class="op"><</span><span class="self">Self</span><span class="op">></span>)
<span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span><span class="op">>></span> {
<span class="kw">let</span> <span class="ident">err</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> <span class="op">=</span> <span class="self">self</span>;
<span class="op"><</span><span class="ident">Error</span><span class="op">></span>::<span class="ident">downcast</span>(<span class="ident">err</span>).<span class="ident">map_err</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> <span class="kw">unsafe</span> {
<span class="comment">// reapply the Send marker</span>
<span class="ident">transmute</span>::<span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span>, <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span><span class="op">>></span>(<span class="ident">s</span>)
})
}
}
<span class="kw">impl</span> <span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"error_downcast"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.3.0"</span>)]</span>
<span class="doccomment">/// Attempt to downcast the box to a concrete type.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">downcast</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span><span class="op">></span>(<span class="self">self</span>: <span class="ident">Box</span><span class="op"><</span><span class="self">Self</span><span class="op">></span>)
<span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">Box</span><span class="op"><</span><span class="self">Self</span><span class="op">>></span> {
<span class="kw">let</span> <span class="ident">err</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> <span class="op">=</span> <span class="self">self</span>;
<span class="op"><</span><span class="ident">Error</span><span class="op">></span>::<span class="ident">downcast</span>(<span class="ident">err</span>).<span class="ident">map_err</span>(<span class="op">|</span><span class="ident">s</span><span class="op">|</span> <span class="kw">unsafe</span> {
<span class="comment">// reapply the Send+Sync marker</span>
<span class="ident">transmute</span>::<span class="op"><</span><span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span>, <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span> <span class="op">+</span> <span class="ident">Send</span> <span class="op">+</span> <span class="ident">Sync</span><span class="op">>></span>(<span class="ident">s</span>)
})
}
}
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span>
<span class="kw">mod</span> <span class="ident">tests</span> {
<span class="kw">use</span> <span class="kw">super</span>::<span class="ident">Error</span>;
<span class="kw">use</span> <span class="ident">fmt</span>;
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>, <span class="ident">PartialEq</span>)]</span>
<span class="kw">struct</span> <span class="ident">A</span>;
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>, <span class="ident">PartialEq</span>)]</span>
<span class="kw">struct</span> <span class="ident">B</span>;
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">A</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">"A"</span>)
}
}
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">B</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">"B"</span>)
}
}
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">A</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> { <span class="string">"A-desc"</span> }
}
<span class="kw">impl</span> <span class="ident">Error</span> <span class="kw">for</span> <span class="ident">B</span> {
<span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> { <span class="string">"A-desc"</span> }
}
<span class="attribute">#[<span class="ident">test</span>]</span>
<span class="kw">fn</span> <span class="ident">downcasting</span>() {
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">A</span>;
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">a</span> <span class="kw">as</span> <span class="kw-2">&</span><span class="kw-2">mut</span> (<span class="ident">Error</span> <span class="op">+</span> <span class="lifetime">'static</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">downcast_ref</span>::<span class="op"><</span><span class="ident">A</span><span class="op">></span>(), <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="ident">A</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">downcast_ref</span>::<span class="op"><</span><span class="ident">B</span><span class="op">></span>(), <span class="prelude-val">None</span>);
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">downcast_mut</span>::<span class="op"><</span><span class="ident">A</span><span class="op">></span>(), <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">A</span>));
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">a</span>.<span class="ident">downcast_mut</span>::<span class="op"><</span><span class="ident">B</span><span class="op">></span>(), <span class="prelude-val">None</span>);
<span class="kw">let</span> <span class="ident">a</span>: <span class="ident">Box</span><span class="op"><</span><span class="ident">Error</span><span class="op">></span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">new</span>(<span class="ident">A</span>);
<span class="kw">match</span> <span class="ident">a</span>.<span class="ident">downcast</span>::<span class="op"><</span><span class="ident">B</span><span class="op">></span>() {
<span class="prelude-val">Ok</span>(..) <span class="op">=></span> <span class="macro">panic</span><span class="macro">!</span>(<span class="string">"expected error"</span>),
<span class="prelude-val">Err</span>(<span class="ident">e</span>) <span class="op">=></span> <span class="macro">assert_eq</span><span class="macro">!</span>(<span class="kw-2">*</span><span class="ident">e</span>.<span class="ident">downcast</span>::<span class="op"><</span><span class="ident">A</span><span class="op">></span>().<span class="ident">unwrap</span>(), <span class="ident">A</span>),
}
}
}
</pre>
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