<!DOCTYPE html><htmllang="en"><head><metacharset="utf-8"><metaname="viewport"content="width=device-width, initial-scale=1.0"><metaname="generator"content="rustdoc"><metaname="description"content="Panics the current thread."><title>panic in anstream - Rust</title><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><linkrel="preload"as="font"type="font/woff2"crossoriginhref="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><linkrel="stylesheet"href="../static.files/normalize-76eba96aa4d2e634.css"><linkrel="stylesheet"href="../static.files/rustdoc-ac92e1bbe349e143.css"><metaname="rustdoc-vars"data-root-path="../"data-static-root-path="../static.files/"data-current-crate="anstream"data-themes=""data-resource-suffix=""data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)"data-channel="1.76.0"data-search-js="search-2b6ce74ff89ae146.js"data-settings-js="settings-4313503d2e1961c2.js"><scriptsrc="../static.files/storage-f2adc0d6ca4d09fb.js"></script><scriptdefersrc="sidebar-items.js"></script><scriptdefersrc="../static.files/main-305769736d49e732.js"></script><noscript><linkrel="stylesheet"href="../static.files/noscript-feafe1bb7466e4bd.css"></noscript><linkrel="alternate icon"type="image/png"href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><linkrel="alternate icon"type="image/png"href="../static.files/favicon-32x32-422f7d1d52889060.png"><linkrel="icon"type="image/svg+xml"href="../static.files/favicon-2c020d218678b618.svg"></head><bodyclass="rustdoc macro"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><navclass="mobile-topbar"><buttonclass="sidebar-menu-toggle">☰</button></nav><navclass="sidebar"><divclass="sidebar-crate"><h2><ahref="../anstream/index.html">anstream</a><spanclass="version">0.6.12</span></h2></div><divclass="sidebar-elems"></div></nav><divclass="sidebar-resizer"></div>
<main><divclass="width-limiter"><navclass="sub"><formclass="search-form"><span></span><divid="sidebar-button"tabindex="-1"><ahref="../anstream/all.html"title="show sidebar"></a></div><inputclass="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"><divid="help-button"tabindex="-1"><ahref="../help.html"title="help">?</a></div><divid="settings-menu"tabindex="-1"><ahref="../settings.html"title="settings"><imgwidth="22"height="22"alt="Change settings"src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><sectionid="main-content"class="content"><divclass="main-heading"><h1>Macro <ahref="index.html">anstream</a>::<wbr><aclass="macro"href="#">panic</a><buttonid="copy-path"title="Copy item path to clipboard"><imgsrc="../static.files/clipboard-7571035ce49a181d.svg"width="19"height="18"alt="Copy item path"></button></h1><spanclass="out-of-band"><aclass="src"href="../src/anstream/macros.rs.html#371-389">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><preclass="rust item-decl"><spanclass="macro">macro_rules! </span>panic {
}</pre><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="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
<ahref="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html#method.unwrap"title="method core::option::Option::unwrap"><code>Option</code></a> and <ahref="https://doc.rust-lang.org/1.76.0/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 <ahref="https://doc.rust-lang.org/1.76.0/core/option/enum.Option.html#variant.None"title="variant core::option::Option::None"><code>None</code></a> or <ahref="https://doc.rust-lang.org/1.76.0/core/result/enum.Result.html#variant.Err"title="variant core::result::Result::Err"><code>Err</code></a> variants.</p>
<p>When using <code>panic!()</code> you can specify a string payload, that is built using
the <ahref="../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 <ahref="../std/panic/fn.set_hook.html"><code>std::panic::set_hook()</code></a>.
Inside the hook a panic can be accessed as a <code>&dyn Any + Send</code>,
which contains either a <code>&str</code> or <code>String</code> for regular <code>panic!()</code> invocations.
To panic with a value of another other type, <ahref="../std/panic/fn.panic_any.html"><code>panic_any</code></a> can be used.</p>
<p>See also the macro <ahref="https://doc.rust-lang.org/1.76.0/core/macro.compile_error.html"title="macro core::compile_error"><code>compile_error!</code></a>, for raising errors during compilation.</p>
<h2id="when-to-use-panic-vs-result"><ahref="#when-to-use-panic-vs-result">When to use <code>panic!</code> vs <code>Result</code></a></h2>
<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 <ahref="../book/ch09-00-error-handling.html">book</a> or the
<divclass="example-wrap should_panic"><ahref="#"class="tooltip"title="This example panics">ⓘ</a><preclass="rust rust-example-rendered"><code><spanclass="kw">use </span>anstream::panic;
<spanclass="macro">panic!</span>();
<spanclass="macro">panic!</span>(<spanclass="string">"this is a terrible mistake!"</span>);
<spanclass="macro">panic!</span>(<spanclass="string">"this is a {} {message}"</span>, <spanclass="string">"fancy"</span>, message = <spanclass="string">"message"</span>);</code></pre></div>
