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<!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="API documentation for the Rust `anyhow` crate."><meta name="keywords" content="rust, rustlang, rust-lang, anyhow"><title>anyhow - Rust</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><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[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='../anyhow/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><p class='location'>Crate anyhow</p><div class="sidebar-elems"><a id='all-types' href='all.html'><p>See all anyhow's items</p></a><div class="block items"><ul><li><a href="#reexports">Re-exports</a></li><li><a href="#macros">Macros</a></li><li><a href="#structs">Structs</a></li><li><a href="#traits">Traits</a></li><li><a href="#types">Type Definitions</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'anyhow', ty: 'mod', relpath: '../'};</script></div></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"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><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"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../src/anyhow/lib.rs.html#1-612' title='goto source code'>[src]</a></span><span class='in-band'>Crate <a class="mod" href=''>anyhow</a></span></h1><div class='docblock'><p><a href="https://github.com/dtolnay/anyhow"><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/anyhow"><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/anyhow"><img src="https://img.shields.io/badge/docs.rs-66c2a5?style=for-the-badge&labelColor=555555&logoColor=white&logo=data:image/svg+xml;base64,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" alt="docs-rs" /></a></p>
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<br>
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<p>This library provides [<code>anyhow::Error</code>][Error], a trait object based error
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type for easy idiomatic error handling in Rust applications.</p>
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<br>
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<h1 id="details" class="section-header"><a href="#details">Details</a></h1>
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<ul>
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<li>
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<p>Use <code>Result<T, anyhow::Error></code>, or equivalently <code>anyhow::Result<T></code>, as
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the return type of any fallible function.</p>
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<p>Within the function, use <code>?</code> to easily propagate any error that implements
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the <code>std::error::Error</code> trait.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">anyhow</span>::<span class="prelude-ty">Result</span>;
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<span class="kw">fn</span> <span class="ident">get_cluster_info</span>() <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">ClusterMap</span><span class="op">></span> {
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<span class="kw">let</span> <span class="ident">config</span> <span class="op">=</span> <span class="ident">std</span>::<span class="ident">fs</span>::<span class="ident">read_to_string</span>(<span class="string">"cluster.json"</span>)<span class="question-mark">?</span>;
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<span class="kw">let</span> <span class="ident">map</span>: <span class="ident">ClusterMap</span> <span class="op">=</span> <span class="ident">serde_json</span>::<span class="ident">from_str</span>(<span class="kw-2">&</span><span class="ident">config</span>)<span class="question-mark">?</span>;
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<span class="prelude-val">Ok</span>(<span class="ident">map</span>)
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}</pre></div>
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</li>
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<li>
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<p>Attach context to help the person troubleshooting the error understand
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where things went wrong. A low-level error like "No such file or
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directory" can be annoying to debug without more context about what higher
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level step the application was in the middle of.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">anyhow</span>::{<span class="ident">Context</span>, <span class="prelude-ty">Result</span>};
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<span class="kw">fn</span> <span class="ident">main</span>() <span class="op">-</span><span class="op">></span> <span class="prelude-ty">Result</span><span class="op"><</span>()<span class="op">></span> {
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...
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<span class="ident">it</span>.<span class="ident">detach</span>().<span class="ident">context</span>(<span class="string">"Failed to detach the important thing"</span>)<span class="question-mark">?</span>;
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<span class="kw">let</span> <span class="ident">content</span> <span class="op">=</span> <span class="ident">std</span>::<span class="ident">fs</span>::<span class="ident">read</span>(<span class="ident">path</span>)
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.<span class="ident">with_context</span>(<span class="op">|</span><span class="op">|</span> <span class="macro">format</span><span class="macro">!</span>(<span class="string">"Failed to read instrs from {}"</span>, <span class="ident">path</span>))<span class="question-mark">?</span>;
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...
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}</pre></div>
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<pre><code class="language-console">Error: Failed to read instrs from ./path/to/instrs.json
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Caused by:
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No such file or directory (os error 2)
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</code></pre>
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</li>
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<li>
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<p>Downcasting is supported and can be by value, by shared reference, or by
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mutable reference as needed.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="comment">// If the error was caused by redaction, then return a</span>
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<span class="comment">// tombstone instead of the content.</span>
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<span class="kw">match</span> <span class="ident">root_cause</span>.<span class="ident">downcast_ref</span>::<span class="op"><</span><span class="ident">DataStoreError</span><span class="op">></span>() {
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<span class="prelude-val">Some</span>(<span class="ident">DataStoreError</span>::<span class="ident">Censored</span>(<span class="kw">_</span>)) <span class="op">=</span><span class="op">></span> <span class="prelude-val">Ok</span>(<span class="ident">Poll</span>::<span class="ident">Ready</span>(<span class="ident">REDACTED_CONTENT</span>)),
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<span class="prelude-val">None</span> <span class="op">=</span><span class="op">></span> <span class="prelude-val">Err</span>(<span class="ident">error</span>),
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}</pre></div>
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</li>
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<li>
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<p>If using the nightly channel, a backtrace is captured and printed with the
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error if the underlying error type does not already provide its own. In
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order to see backtraces, they must be enabled through the environment
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variables described in <a href="https://doc.rust-lang.org/std/backtrace/index.html#environment-variables"><code>std::backtrace</code></a>:</p>
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<ul>
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<li>If you want panics and errors to both have backtraces, set
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<code>RUST_BACKTRACE=1</code>;</li>
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<li>If you want only errors to have backtraces, set <code>RUST_LIB_BACKTRACE=1</code>;</li>
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<li>If you want only panics to have backtraces, set <code>RUST_BACKTRACE=1</code> and
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<code>RUST_LIB_BACKTRACE=0</code>.</li>
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</ul>
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<p>The tracking issue for this feature is <a href="https://github.com/rust-lang/rust/issues/53487">rust-lang/rust#53487</a>.</p>
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</li>
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<li>
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<p>Anyhow works with any error type that has an impl of <code>std::error::Error</code>,
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including ones defined in your crate. We do not bundle a <code>derive(Error)</code>
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macro but you can write the impls yourself or use a standalone macro like
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<a href="https://github.com/dtolnay/thiserror">thiserror</a>.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">thiserror</span>::<span class="ident">Error</span>;
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<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Error</span>, <span class="ident">Debug</span>)]</span>
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<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">FormatError</span> {
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<span class="attribute">#[<span class="ident">error</span>(<span class="string">"Invalid header (expected {expected:?}, got {found:?})"</span>)]</span>
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<span class="ident">InvalidHeader</span> {
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<span class="ident">expected</span>: <span class="ident">String</span>,
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<span class="ident">found</span>: <span class="ident">String</span>,
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},
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<span class="attribute">#[<span class="ident">error</span>(<span class="string">"Missing attribute: {0}"</span>)]</span>
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<span class="ident">MissingAttribute</span>(<span class="ident">String</span>),
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}</pre></div>
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</li>
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<li>
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<p>One-off error messages can be constructed using the <code>anyhow!</code> macro, which
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supports string interpolation and produces an <code>anyhow::Error</code>.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="macro">anyhow</span><span class="macro">!</span>(<span class="string">"Missing attribute: {}"</span>, <span class="ident">missing</span>));</pre></div>
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</li>
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</ul>
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<br>
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<h1 id="no-std-support" class="section-header"><a href="#no-std-support">No-std support</a></h1>
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<p>In no_std mode, the same API is almost all available and works the same way.
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To depend on Anyhow in no_std mode, disable our default enabled "std"
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feature in Cargo.toml. A global allocator is required.</p>
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<pre><code class="language-toml">[dependencies]
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anyhow = { version = "1.0", default-features = false }
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</code></pre>
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<p>Since the <code>?</code>-based error conversions would normally rely on the
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<code>std::error::Error</code> trait which is only available through std, no_std mode
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will require an explicit <code>.map_err(Error::msg)</code> when working with a
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non-Anyhow error type inside a function that returns Anyhow's error type.</p>
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</div><h2 id='reexports' class='section-header'><a href="#reexports">Re-exports</a></h2>
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<table><tr><td><code>pub use <a class="macro" href="../anyhow/macro.anyhow.html" title="macro anyhow::anyhow">anyhow</a> as format_err;</code></td></tr></table><h2 id='macros' class='section-header'><a href="#macros">Macros</a></h2>
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<table><tr class='module-item'><td><a class="macro" href="macro.anyhow.html" title='anyhow::anyhow macro'>anyhow</a></td><td class='docblock-short'><p>Construct an ad-hoc error from a string.</p>
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</td></tr><tr class='module-item'><td><a class="macro" href="macro.bail.html" title='anyhow::bail macro'>bail</a></td><td class='docblock-short'><p>Return early with an error.</p>
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</td></tr><tr class='module-item'><td><a class="macro" href="macro.ensure.html" title='anyhow::ensure macro'>ensure</a></td><td class='docblock-short'><p>Return early with an error if a condition is not satisfied.</p>
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</td></tr></table><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table><tr class='module-item'><td><a class="struct" href="struct.Chain.html" title='anyhow::Chain struct'>Chain</a></td><td class='docblock-short'><p>Iterator of a chain of source errors.</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.Error.html" title='anyhow::Error struct'>Error</a></td><td class='docblock-short'><p>The <code>Error</code> type, a wrapper around a dynamic error type.</p>
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</td></tr></table><h2 id='traits' class='section-header'><a href="#traits">Traits</a></h2>
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<table><tr class='module-item'><td><a class="trait" href="trait.Context.html" title='anyhow::Context trait'>Context</a></td><td class='docblock-short'><p>Provides the <code>context</code> method for <code>Result</code>.</p>
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</td></tr></table><h2 id='types' class='section-header'><a href="#types">Type Definitions</a></h2>
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<table><tr class='module-item'><td><a class="type" href="type.Result.html" title='anyhow::Result type'>Result</a></td><td class='docblock-short'><p><code>Result<T, Error></code></p>
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</td></tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><script>window.rootPath = "../";window.currentCrate = "anyhow";</script><script src="../aliases.js"></script><script src="../main.js"></script><script defer src="../search-index.js"></script></body></html> |