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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="Panics the current thread."><title>panic in anstream - Rust</title><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"><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-5bc39a1768837dd0.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="anstream" data-themes="" data-resource-suffix="" data-rustdoc-version="1.77.0 (aedd173a2 2024-03-17)" data-channel="1.77.0" data-search-js="search-dd67cee4cfa65049.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-4c98445ec4002617.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-48f368f3872407c8.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 macro"><!--[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="../anstream/index.html">anstream</a><span class="version">0.6.13</span></h2></div><div class="sidebar-elems"></div></nav><div class="sidebar-resizer"></div>
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<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../anstream/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>Macro <a href="index.html">anstream</a>::<wbr><a class="macro" href="#">panic</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/anstream/macros.rs.html#371-389">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>&#x2212;</span>]</button></span></div><pre class="rust item-decl"><span class="macro">macro_rules! </span>panic {
() =&gt; { ... };
($(<span class="macro-nonterminal">$arg</span>:tt)<span class="kw-2">*</span>) =&gt; { ... };
}</pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Panics the current thread.</p>
<p>This allows a program to terminate immediately and provide feedback
to the caller of the program.</p>
<p>This macro is the perfect way to assert conditions in example code and in
tests. <code>panic!</code> is closely tied with the <code>unwrap</code> method of both
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<a href="https://doc.rust-lang.org/1.77.0/core/option/enum.Option.html#method.unwrap" title="method core::option::Option::unwrap"><code>Option</code></a> and <a href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html#method.unwrap" title="method core::result::Result::unwrap"><code>Result</code></a> enums. Both implementations call
<code>panic!</code> when they are set to <a href="https://doc.rust-lang.org/1.77.0/core/option/enum.Option.html#variant.None" title="variant core::option::Option::None"><code>None</code></a> or <a href="https://doc.rust-lang.org/1.77.0/core/result/enum.Result.html#variant.Err" title="variant core::result::Result::Err"><code>Err</code></a> variants.</p>
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<p>When using <code>panic!()</code> you can specify a string payload, that is built using
the <a href="../std/macro.format.html"><code>format!</code></a> syntax. That payload is used when injecting the panic into
the calling Rust thread, causing the thread to panic entirely.</p>
<p>The behavior of the default <code>std</code> hook, i.e. the code that runs directly
after the panic is invoked, is to print the message payload to
<code>stderr</code> along with the file/line/column information of the <code>panic!()</code>
call. You can override the panic hook using <a href="../std/panic/fn.set_hook.html"><code>std::panic::set_hook()</code></a>.
Inside the hook a panic can be accessed as a <code>&amp;dyn Any + Send</code>,
which contains either a <code>&amp;str</code> or <code>String</code> for regular <code>panic!()</code> invocations.
To panic with a value of another other type, <a href="../std/panic/fn.panic_any.html"><code>panic_any</code></a> can be used.</p>
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<p>See also the macro <a href="https://doc.rust-lang.org/1.77.0/core/macro.compile_error.html" title="macro core::compile_error"><code>compile_error!</code></a>, for raising errors during compilation.</p>
<h2 id="when-to-use-panic-vs-result"><a class="doc-anchor" href="#when-to-use-panic-vs-result">§</a>When to use <code>panic!</code> vs <code>Result</code></h2>
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<p>The Rust language provides two complementary systems for constructing /
representing, reporting, propagating, reacting to, and discarding errors. These
responsibilities are collectively known as “error handling.” <code>panic!</code> and
<code>Result</code> are similar in that they are each the primary interface of their
respective error handling systems; however, the meaning these interfaces attach
to their errors and the responsibilities they fulfill within their respective
error handling systems differ.</p>
<p>The <code>panic!</code> macro is used to construct errors that represent a bug that has
been detected in your program. With <code>panic!</code> you provide a message that
describes the bug and the language then constructs an error with that message,
reports it, and propagates it for you.</p>
<p><code>Result</code> on the other hand is used to wrap other types that represent either
the successful result of some computation, <code>Ok(T)</code>, or error types that
represent an anticipated runtime failure mode of that computation, <code>Err(E)</code>.
<code>Result</code> is used alongside user defined types which represent the various
anticipated runtime failure modes that the associated computation could
encounter. <code>Result</code> must be propagated manually, often with the the help of the
<code>?</code> operator and <code>Try</code> trait, and they must be reported manually, often with
the help of the <code>Error</code> trait.</p>
<p>For more detailed information about error handling check out the <a href="../book/ch09-00-error-handling.html">book</a> or the
<a href="../std/result/index.html"><code>std::result</code></a> module docs.</p>
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<h2 id="current-implementation"><a class="doc-anchor" href="#current-implementation">§</a>Current implementation</h2>
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<p>If the main thread panics it will terminate all your threads and end your
program with code <code>101</code>.</p>
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<h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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<div class="example-wrap should_panic"><a href="#" class="tooltip" title="This example panics">ⓘ</a><pre class="rust rust-example-rendered"><code><span class="kw">use </span>anstream::panic;
<span class="macro">panic!</span>();
<span class="macro">panic!</span>(<span class="string">"this is a terrible mistake!"</span>);
<span class="macro">panic!</span>(<span class="string">"this is a {} {message}"</span>, <span class="string">"fancy"</span>, message = <span class="string">"message"</span>);</code></pre></div>
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