| <!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="Generates a random value using the thread-local random number generator."><meta name="keywords" content="rust, rustlang, rust-lang, random"><title>random in rand - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../SourceCodePro-Semibold.ttf.woff2"><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="../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../dark.css" disabled><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script src="../crates.js"></script><script defer src="../main.js"></script> |
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| </a><div class="sidebar-elems"><h2 class="location">Other items in<br><a href="index.html">rand</a></h2><div id="sidebar-vars" data-name="random" data-ty="fn" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../rand/index.html"><img src="https://www.rust-lang.org/logos/rust-logo-128x128-blk.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../brush.svg"></button><div id="theme-choices" role="menu"></div></div><form class="search-form"><div class="search-container"><div> |
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| <h1 class="fqn"><span class="in-band">Function <a href="index.html">rand</a>::<wbr><a class="fn" href="#">random</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span></h1><span class="out-of-band"> |
| <a class="srclink" href="../src/rand/lib.rs.html#184-187" title="goto source code">source</a> · |
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| <div class="docblock item-decl"><pre class="rust fn"><code>pub fn random<T>() -> T <span class="where fmt-newline">where<br> <a class="struct" href="distributions/struct.Standard.html" title="struct rand::distributions::Standard">Standard</a>: <a class="trait" href="distributions/trait.Distribution.html" title="trait rand::distributions::Distribution">Distribution</a><T>, </span></code></pre></div><div class="item-info"><div class="stab portability">This is supported on <strong>crate features <code>std</code> and <code>std_rng</code></strong> only.</div></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Generates a random value using the thread-local random number generator.</p> |
| <p>This is simply a shortcut for <code>thread_rng().gen()</code>. See <a href="fn.thread_rng.html" title="thread_rng"><code>thread_rng</code></a> for |
| documentation of the entropy source and <a href="distributions/struct.Standard.html"><code>Standard</code></a> for documentation of |
| distributions and type-specific generation.</p> |
| <h2 id="provided-implementations" class="section-header"><a href="#provided-implementations">Provided implementations</a></h2> |
| <p>The following types have provided implementations that |
| generate values with the following ranges and distributions:</p> |
| <ul> |
| <li>Integers (<code>i32</code>, <code>u32</code>, <code>isize</code>, <code>usize</code>, etc.): Uniformly distributed |
| over all values of the type.</li> |
| <li><code>char</code>: Uniformly distributed over all Unicode scalar values, i.e. all |
| code points in the range <code>0...0x10_FFFF</code>, except for the range |
| <code>0xD800...0xDFFF</code> (the surrogate code points). This includes |
| unassigned/reserved code points.</li> |
| <li><code>bool</code>: Generates <code>false</code> or <code>true</code>, each with probability 0.5.</li> |
| <li>Floating point types (<code>f32</code> and <code>f64</code>): Uniformly distributed in the |
| half-open range <code>[0, 1)</code>. See notes below.</li> |
| <li>Wrapping integers (<code>Wrapping<T></code>), besides the type identical to their |
| normal integer variants.</li> |
| </ul> |
| <p>Also supported is the generation of the following |
| compound types where all component types are supported:</p> |
| <ul> |
| <li>Tuples (up to 12 elements): each element is generated sequentially.</li> |
| <li>Arrays (up to 32 elements): each element is generated sequentially; |
| see also <a href="trait.Rng.html#method.fill" title="Rng::fill"><code>Rng::fill</code></a> which supports arbitrary array length for integer |
| types and tends to be faster for <code>u32</code> and smaller types.</li> |
| <li><code>Option<T></code> first generates a <code>bool</code>, and if true generates and returns |
| <code>Some(value)</code> where <code>value: T</code>, otherwise returning <code>None</code>.</li> |
| </ul> |
| <h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="ident">rand::random</span>::<span class="op"><</span><span class="ident">u8</span><span class="op">></span>(); |
| <span class="macro">println!</span>(<span class="string">"{}"</span>, <span class="ident">x</span>); |
| |
| <span class="kw">let</span> <span class="ident">y</span> <span class="op">=</span> <span class="ident">rand::random</span>::<span class="op"><</span><span class="ident">f64</span><span class="op">></span>(); |
| <span class="macro">println!</span>(<span class="string">"{}"</span>, <span class="ident">y</span>); |
| |
| <span class="kw">if</span> <span class="ident">rand::random</span>() { <span class="comment">// generates a boolean</span> |
| <span class="macro">println!</span>(<span class="string">"Better lucky than good!"</span>); |
| }</code></pre></div> |
| <p>If you’re calling <code>random()</code> in a loop, caching the generator as in the |
| following example can increase performance.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">rand::Rng</span>; |
| |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">v</span> <span class="op">=</span> <span class="macro">vec!</span>[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]; |
| |
| <span class="kw">for</span> <span class="ident">x</span> <span class="kw">in</span> <span class="ident">v</span>.<span class="ident">iter_mut</span>() { |
| <span class="kw-2">*</span><span class="ident">x</span> <span class="op">=</span> <span class="ident">rand::random</span>() |
| } |
| |
| <span class="comment">// can be made faster by caching thread_rng</span> |
| |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">rng</span> <span class="op">=</span> <span class="ident">rand::thread_rng</span>(); |
| |
| <span class="kw">for</span> <span class="ident">x</span> <span class="kw">in</span> <span class="ident">v</span>.<span class="ident">iter_mut</span>() { |
| <span class="kw-2">*</span><span class="ident">x</span> <span class="op">=</span> <span class="ident">rng</span>.<span class="ident">gen</span>(); |
| }</code></pre></div> |
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