mirror of
https://github.com/edg-l/edlang.git
synced 2024-11-23 00:18:24 +00:00
164 lines
12 KiB
HTML
164 lines
12 KiB
HTML
<!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="github crates-io docs-rs"><title>thiserror - Rust</title><script> if (window.location.protocol !== "file:") document.write(`<link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2">`)</script><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-e935ef01ae1c1829.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="thiserror" data-themes="" data-resource-suffix="" data-rustdoc-version="1.78.0 (9b00956e5 2024-04-29)" data-channel="1.78.0" data-search-js="search-42d8da7a6b9792c2.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-4c98445ec4002617.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-12cf3b4f4f9dc36d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-04d5337699b92874.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc mod crate"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle" title="show sidebar"></button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../thiserror/index.html">thiserror</a><span class="version">1.0.61</span></h2></div><div class="sidebar-elems"><ul class="block">
|
||
<li><a id="all-types" href="all.html">All Items</a></li></ul><section><ul class="block"><li><a href="#derives">Derive Macros</a></li></ul></section></div></nav><div class="sidebar-resizer"></div>
|
||
<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../thiserror/all.html" title="show sidebar"></a></div><input class="search-input" name="search" aria-label="Run search in the documentation" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" tabindex="-1"><a href="../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Crate <a class="mod" href="#">thiserror</a><button id="copy-path" title="Copy item path to clipboard"><img src="../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../src/thiserror/lib.rs.html#1-260">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p><a href="https://github.com/dtolnay/thiserror"><img src="https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github" alt="github" /></a> <a href="https://crates.io/crates/thiserror"><img src="https://img.shields.io/badge/crates.io-fc8d62?style=for-the-badge&labelColor=555555&logo=rust" alt="crates-io" /></a> <a href="https://docs.rs/thiserror"><img src="https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" alt="docs-rs" /></a></p>
|
||
<br>
|
||
<p>This library provides a convenient derive macro for the standard library’s
|
||
<a href="https://doc.rust-lang.org/std/error/trait.Error.html"><code>std::error::Error</code></a> trait.</p>
|
||
<br>
|
||
<h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2>
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>thiserror::Error;
|
||
|
||
<span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub enum </span>DataStoreError {
|
||
<span class="attr">#[error(<span class="string">"data store disconnected"</span>)]
|
||
</span>Disconnect(<span class="attr">#[from] </span>io::Error),
|
||
<span class="attr">#[error(<span class="string">"the data for key `{0}` is not available"</span>)]
|
||
</span>Redaction(String),
|
||
<span class="attr">#[error(<span class="string">"invalid header (expected {expected:?}, found {found:?})"</span>)]
|
||
</span>InvalidHeader {
|
||
expected: String,
|
||
found: String,
|
||
},
|
||
<span class="attr">#[error(<span class="string">"unknown data store error"</span>)]
|
||
</span>Unknown,
|
||
}</code></pre></div>
|
||
<br>
|
||
<h2 id="details"><a class="doc-anchor" href="#details">§</a>Details</h2>
|
||
<ul>
|
||
<li>
|
||
<p>Thiserror deliberately does not appear in your public API. You get the
|
||
same thing as if you had written an implementation of <code>std::error::Error</code>
|
||
by hand, and switching from handwritten impls to thiserror or vice versa
|
||
is not a breaking change.</p>
|
||
</li>
|
||
<li>
|
||
<p>Errors may be enums, structs with named fields, tuple structs, or unit
|
||
structs.</p>
|
||
</li>
|
||
<li>
|
||
<p>A <code>Display</code> impl is generated for your error if you provide
|
||
<code>#[error("...")]</code> messages on the struct or each variant of your enum, as
|
||
shown above in the example.</p>
|
||
<p>The messages support a shorthand for interpolating fields from the error.</p>
|
||
<ul>
|
||
<li><code>#[error("{var}")]</code> ⟶ <code>write!("{}", self.var)</code></li>
|
||
<li><code>#[error("{0}")]</code> ⟶ <code>write!("{}", self.0)</code></li>
|
||
<li><code>#[error("{var:?}")]</code> ⟶ <code>write!("{:?}", self.var)</code></li>
|
||
<li><code>#[error("{0:?}")]</code> ⟶ <code>write!("{:?}", self.0)</code></li>
|
||
</ul>
|
||
<p>These shorthands can be used together with any additional format args,
|
||
which may be arbitrary expressions. For example:</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub enum </span>Error {
|
||
<span class="attr">#[error(<span class="string">"invalid rdo_lookahead_frames {0} (expected < {})"</span>, i32::MAX)]
|
||
</span>InvalidLookahead(u32),
|
||
}</code></pre></div>
|
||
<p>If one of the additional expression arguments needs to refer to a field of
|
||
the struct or enum, then refer to named fields as <code>.var</code> and tuple fields
|
||
as <code>.0</code>.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub enum </span>Error {
|
||
<span class="attr">#[error(<span class="string">"first letter must be lowercase but was {:?}"</span>, first_char(.<span class="number">0</span>))]
|
||
</span>WrongCase(String),
|
||
<span class="attr">#[error(<span class="string">"invalid index {idx}, expected at least {} and at most {}"</span>, .limits.lo, .limits.hi)]
|
||
</span>OutOfBounds { idx: usize, limits: Limits },
|
||
}</code></pre></div>
|
||
</li>
|
||
<li>
|
||
<p>A <code>From</code> impl is generated for each variant containing a <code>#[from]</code>
|
||
attribute.</p>
|
||
<p>Note that the variant must not contain any other fields beyond the source
|
||
error and possibly a backtrace. A backtrace is captured from within the
|
||
<code>From</code> impl if there is a field for it.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub enum </span>MyError {
|
||
Io {
|
||
<span class="attr">#[from]
|
||
</span>source: io::Error,
|
||
backtrace: Backtrace,
|
||
},
|
||
}</code></pre></div>
|
||
</li>
|
||
<li>
|
||
<p>The Error trait’s <code>source()</code> method is implemented to return whichever
|
||
field has a <code>#[source]</code> attribute or is named <code>source</code>, if any. This is
|
||
for identifying the underlying lower level error that caused your error.</p>
|
||
<p>The <code>#[from]</code> attribute always implies that the same field is <code>#[source]</code>,
|
||
so you don’t ever need to specify both attributes.</p>
|
||
<p>Any error type that implements <code>std::error::Error</code> or dereferences to <code>dyn std::error::Error</code> will work as a source.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub struct </span>MyError {
|
||
msg: String,
|
||
<span class="attr">#[source] </span><span class="comment">// optional if field name is `source`
|
||
</span>source: anyhow::Error,
|
||
}</code></pre></div>
|
||
</li>
|
||
<li>
|
||
<p>The Error trait’s <code>provide()</code> method is implemented to provide whichever
|
||
field has a type named <code>Backtrace</code>, if any, as a
|
||
<code>std::backtrace::Backtrace</code>.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::backtrace::Backtrace;
|
||
|
||
<span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub struct </span>MyError {
|
||
msg: String,
|
||
backtrace: Backtrace, <span class="comment">// automatically detected
|
||
</span>}</code></pre></div>
|
||
</li>
|
||
<li>
|
||
<p>If a field is both a source (named <code>source</code>, or has <code>#[source]</code> or
|
||
<code>#[from]</code> attribute) <em>and</em> is marked <code>#[backtrace]</code>, then the Error
|
||
trait’s <code>provide()</code> method is forwarded to the source’s <code>provide</code> so that
|
||
both layers of the error share the same backtrace.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub enum </span>MyError {
|
||
Io {
|
||
<span class="attr">#[backtrace]
|
||
</span>source: io::Error,
|
||
},
|
||
}</code></pre></div>
|
||
</li>
|
||
<li>
|
||
<p>Errors may use <code>error(transparent)</code> to forward the source and Display
|
||
methods straight through to an underlying error without adding an
|
||
additional message. This would be appropriate for enums that need an
|
||
“anything else” variant.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">pub enum </span>MyError {
|
||
...
|
||
|
||
<span class="attr">#[error(transparent)]
|
||
</span>Other(<span class="attr">#[from] </span>anyhow::Error), <span class="comment">// source and Display delegate to anyhow::Error
|
||
</span>}</code></pre></div>
|
||
<p>Another use case is hiding implementation details of an error
|
||
representation behind an opaque error type, so that the representation is
|
||
able to evolve without breaking the crate’s public API.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="comment">// PublicError is public, but opaque and easy to keep compatible.
|
||
</span><span class="attr">#[derive(Error, Debug)]
|
||
#[error(transparent)]
|
||
</span><span class="kw">pub struct </span>PublicError(<span class="attr">#[from] </span>ErrorRepr);
|
||
|
||
<span class="kw">impl </span>PublicError {
|
||
<span class="comment">// Accessors for anything we do want to expose publicly.
|
||
</span>}
|
||
|
||
<span class="comment">// Private and free to change across minor version of the crate.
|
||
</span><span class="attr">#[derive(Error, Debug)]
|
||
</span><span class="kw">enum </span>ErrorRepr {
|
||
...
|
||
}</code></pre></div>
|
||
</li>
|
||
<li>
|
||
<p>See also the <a href="https://github.com/dtolnay/anyhow"><code>anyhow</code></a> library for a convenient single error type to use
|
||
in application code.</p>
|
||
</li>
|
||
</ul>
|
||
</div></details><h2 id="derives" class="section-header">Derive Macros<a href="#derives" class="anchor">§</a></h2><ul class="item-table"><li><div class="item-name"><a class="derive" href="derive.Error.html" title="derive thiserror::Error">Error</a></div></li></ul></section></div></main></body></html> |