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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="An automatically-implemented extension trait on [`RngCore`] providing high-level generic methods for sampling values and other convenience methods."><meta name="keywords" content="rust, rustlang, rust-lang, Rng"><title>Rng 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" href="../normalize.css"><link rel="stylesheet" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../ayu.css" disabled><link rel="stylesheet" href="../dark.css" disabled><link rel="stylesheet" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="icon" href="https://www.rust-lang.org/favicon.ico"></head><body class="rustdoc trait"><!--[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">☰</button><a class="sidebar-logo" href="../rand/index.html"><div class="logo-container"><img src="https://www.rust-lang.org/logos/rust-logo-128x128-blk.png" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../rand/index.html"><div class="logo-container">
<img src="https://www.rust-lang.org/logos/rust-logo-128x128-blk.png" alt="logo"></div></a><h2 class="location"><a href="#">Rng</a></h2><div class="sidebar-elems"><section><h3><a href="#provided-methods">Provided Methods</a></h3><ul class="block"><li><a href="#method.fill">fill</a></li><li><a href="#method.gen">gen</a></li><li><a href="#method.gen_bool">gen_bool</a></li><li><a href="#method.gen_range">gen_range</a></li><li><a href="#method.gen_ratio">gen_ratio</a></li><li><a href="#method.sample">sample</a></li><li><a href="#method.sample_iter">sample_iter</a></li><li><a href="#method.try_fill">try_fill</a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><h2><a href="index.html">In rand</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../wheel.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Trait <a href="index.html">rand</a>::<wbr><a class="trait" href="#">Rng</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></h1><span class="out-of-band"><a class="srclink" href="../src/rand/rng.rs.html#55-303">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust trait"><code>pub trait Rng: <a class="trait" href="trait.RngCore.html" title="trait rand::RngCore">RngCore</a> {
fn <a href="#method.gen" class="fnname">gen</a><T>(&mut self) -> T<br> <span class="where">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>,
{ ... }
<span class="item-spacer"></span> fn <a href="#method.gen_range" class="fnname">gen_range</a><T, R>(&mut self, range: R) -> T<br> <span class="where">where<br> T: <a class="trait" href="distributions/uniform/trait.SampleUniform.html" title="trait rand::distributions::uniform::SampleUniform">SampleUniform</a>,<br> R: <a class="trait" href="distributions/uniform/trait.SampleRange.html" title="trait rand::distributions::uniform::SampleRange">SampleRange</a><T></span>,
{ ... }
<span class="item-spacer"></span> fn <a href="#method.sample" class="fnname">sample</a><T, D: <a class="trait" href="distributions/trait.Distribution.html" title="trait rand::distributions::Distribution">Distribution</a><T>>(&mut self, distr: D) -> T { ... }
<span class="item-spacer"></span> fn <a href="#method.sample_iter" class="fnname">sample_iter</a><T, D>(self, distr: D) -> <a class="struct" href="distributions/struct.DistIter.html" title="struct rand::distributions::DistIter">DistIter</a><D, Self, T><span class="notable-traits"><span class="notable-traits-tooltip">ⓘ<span class="notable-traits-tooltiptext"><span class="docblock"><span class="notable">Notable traits for <a class="struct" href="distributions/struct.DistIter.html" title="struct rand::distributions::DistIter">DistIter</a><D, R, T></span><code class="content"><span class="where fmt-newline">impl<D, R, T> <a class="trait" href="https://doc.rust-lang.org/1.66.0/core/iter/traits/iterator/trait.Iterator.html" title="trait core::iter::traits::iterator::Iterator">Iterator</a> for <a class="struct" href="distributions/struct.DistIter.html" title="struct rand::distributions::DistIter">DistIter</a><D, R, T><span class="where fmt-newline">where<br> D: <a class="trait" href="distributions/trait.Distribution.html" title="trait rand::distributions::Distribution">Distribution</a><T>,<br> R: <a class="trait" href="trait.Rng.html" title="trait rand::Rng">Rng</a>,</span></span><span class="where fmt-newline"> type <a href="https://doc.rust-lang.org/1.66.0/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" class="associatedtype">Item</a> = T;</span></code></span></span></span></span><br> <span class="where">where<br> D: <a class="trait" href="distributions/trait.Distribution.html" title="trait rand::distributions::Distribution">Distribution</a><T>,<br> Self: <a class="trait" href="https://doc.rust-lang.org/1.66.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a></span>,
{ ... }
<span class="item-spacer"></span> fn <a href="#method.fill" class="fnname">fill</a><T: <a class="trait" href="trait.Fill.html" title="trait rand::Fill">Fill</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.66.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, dest: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.reference.html">&mut </a>T) { ... }
<span class="item-spacer"></span> fn <a href="#method.try_fill" class="fnname">try_fill</a><T: <a class="trait" href="trait.Fill.html" title="trait rand::Fill">Fill</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.66.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, dest: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.reference.html">&mut </a>T) -> <a class="enum" href="https://doc.rust-lang.org/1.66.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.unit.html">()</a>, <a class="struct" href="struct.Error.html" title="struct rand::Error">Error</a>> { ... }
<span class="item-spacer"></span> fn <a href="#method.gen_bool" class="fnname">gen_bool</a>(&mut self, p: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.f64.html">f64</a>) -> <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.bool.html">bool</a> { ... }
<span class="item-spacer"></span> fn <a href="#method.gen_ratio" class="fnname">gen_ratio</a>(&mut self, numerator: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.u32.html">u32</a>, denominator: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.u32.html">u32</a>) -> <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.bool.html">bool</a> { ... }
}</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>An automatically-implemented extension trait on <a href="trait.RngCore.html" title="RngCore"><code>RngCore</code></a> providing high-level
generic methods for sampling values and other convenience methods.</p>
<p>This is the primary trait to use when generating random values.</p>
<h2 id="generic-usage"><a href="#generic-usage">Generic usage</a></h2>
<p>The basic pattern is <code>fn foo<R: Rng + ?Sized>(rng: &mut R)</code>. Some
things are worth noting here:</p>
<ul>
<li>Since <code>Rng: RngCore</code> and every <code>RngCore</code> implements <code>Rng</code>, it makes no
difference whether we use <code>R: Rng</code> or <code>R: RngCore</code>.</li>
<li>The <code>+ ?Sized</code> un-bounding allows functions to be called directly on
type-erased references; i.e. <code>foo(r)</code> where <code>r: &mut dyn RngCore</code>. Without
this it would be necessary to write <code>foo(&mut r)</code>.</li>
</ul>
<p>An alternative pattern is possible: <code>fn foo<R: Rng>(rng: R)</code>. This has some
trade-offs. It allows the argument to be consumed directly without a <code>&mut</code>
(which is how <code>from_rng(thread_rng())</code> works); also it still works directly
on references (including type-erased references). Unfortunately within the
function <code>foo</code> it is not known whether <code>rng</code> is a reference type or not,
hence many uses of <code>rng</code> require an extra reference, either explicitly
(<code>distr.sample(&mut rng)</code>) or implicitly (<code>rng.gen()</code>); one may hope the
optimiser can remove redundant references later.</p>
<p>Example:</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::Rng;
<span class="kw">fn </span>foo<R: Rng + <span class="question-mark">?</span>Sized>(rng: <span class="kw-2">&mut </span>R) -> f32 {
rng.gen()
}
</code></pre></div>
</div></details><h2 id="provided-methods" class="small-section-header">Provided Methods<a href="#provided-methods" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.gen" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#93-96">source</a><h4 class="code-header">fn <a href="#method.gen" class="fnname">gen</a><T>(&mut self) -> 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></h4></section></summary><div class="docblock"><p>Return a random value supporting the <a href="distributions/struct.Standard.html"><code>Standard</code></a> distribution.</p>
<h5 id="example"><a href="#example">Example</a></h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">let </span><span class="kw-2">mut </span>rng = thread_rng();
<span class="kw">let </span>x: u32 = rng.gen();
<span class="macro">println!</span>(<span class="string">"{}"</span>, x);
<span class="macro">println!</span>(<span class="string">"{:?}"</span>, rng.gen::<(f64, bool)>());</code></pre></div>
<h5 id="arrays-and-tuples"><a href="#arrays-and-tuples">Arrays and tuples</a></h5>
<p>The <code>rng.gen()</code> method is able to generate arrays (up to 32 elements)
and tuples (up to 12 elements), so long as all element types can be
generated.
When using <code>rustc</code> ≥ 1.51, enable the <code>min_const_gen</code> feature to support
arrays larger than 32 elements.</p>
<p>For arrays of integers, especially for those with small element types
(< 64 bit), it will likely be faster to instead use <a href="trait.Rng.html#method.fill" title="Rng::fill"><code>Rng::fill</code></a>.</p>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">let </span><span class="kw-2">mut </span>rng = thread_rng();
<span class="kw">let </span>tuple: (u8, i32, char) = rng.gen(); <span class="comment">// arbitrary tuple support
</span><span class="kw">let </span>arr1: [f32; <span class="number">32</span>] = rng.gen(); <span class="comment">// array construction
</span><span class="kw">let </span><span class="kw-2">mut </span>arr2 = [<span class="number">0u8</span>; <span class="number">128</span>];
rng.fill(<span class="kw-2">&mut </span>arr2); <span class="comment">// array fill</span></code></pre></div>
</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.gen_range" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#129-136">source</a><h4 class="code-header">fn <a href="#method.gen_range" class="fnname">gen_range</a><T, R>(&mut self, range: R) -> T<span class="where fmt-newline">where<br> T: <a class="trait" href="distributions/uniform/trait.SampleUniform.html" title="trait rand::distributions::uniform::SampleUniform">SampleUniform</a>,<br> R: <a class="trait" href="distributions/uniform/trait.SampleRange.html" title="trait rand::distributions::uniform::SampleRange">SampleRange</a><T>,</span></h4></section></summary><div class="docblock"><p>Generate a random value in the given range.</p>
<p>This function is optimised for the case that only a single sample is
made from the given range. See also the <a href="distributions/struct.Uniform.html"><code>Uniform</code></a> distribution
type which may be faster if sampling from the same range repeatedly.</p>
<p>Only <code>gen_range(low..high)</code> and <code>gen_range(low..=high)</code> are supported.</p>
<h5 id="panics"><a href="#panics">Panics</a></h5>
<p>Panics if the range is empty.</p>
<h5 id="example-1"><a href="#example-1">Example</a></h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">let </span><span class="kw-2">mut </span>rng = thread_rng();
<span class="comment">// Exclusive range
</span><span class="kw">let </span>n: u32 = rng.gen_range(<span class="number">0</span>..<span class="number">10</span>);
<span class="macro">println!</span>(<span class="string">"{}"</span>, n);
<span class="kw">let </span>m: f64 = rng.gen_range(-<span class="number">40.0</span>..<span class="number">1.3e5</span>);
<span class="macro">println!</span>(<span class="string">"{}"</span>, m);
<span class="comment">// Inclusive range
</span><span class="kw">let </span>n: u32 = rng.gen_range(<span class="number">0</span>..=<span class="number">10</span>);
<span class="macro">println!</span>(<span class="string">"{}"</span>, n);</code></pre></div>
</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.sample" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#152-154">source</a><h4 class="code-header">fn <a href="#method.sample" class="fnname">sample</a><T, D: <a class="trait" href="distributions/trait.Distribution.html" title="trait rand::distributions::Distribution">Distribution</a><T>>(&mut self, distr: D) -> T</h4></section></summary><div class="docblock"><p>Sample a new value, using the given distribution.</p>
<h6 id="example-2"><a href="#example-2">Example</a></h6>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">use </span>rand::distributions::Uniform;
<span class="kw">let </span><span class="kw-2">mut </span>rng = thread_rng();
<span class="kw">let </span>x = rng.sample(Uniform::new(<span class="number">10u32</span>, <span class="number">15</span>));
<span class="comment">// Type annotation requires two types, the type and distribution; the
// distribution can be inferred.
</span><span class="kw">let </span>y = rng.sample::<u16, <span class="kw">_</span>>(Uniform::new(<span class="number">10</span>, <span class="number">15</span>));</code></pre></div>
</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.sample_iter" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#192-198">source</a><h4 class="code-header">fn <a href="#method.sample_iter" class="fnname">sample_iter</a><T, D>(self, distr: D) -> <a class="struct" href="distributions/struct.DistIter.html" title="struct rand::distributions::DistIter">DistIter</a><D, Self, T><span class="notable-traits"><span class="notable-traits-tooltip">ⓘ<span class="notable-traits-tooltiptext"><span class="docblock"><span class="notable">Notable traits for <a class="struct" href="distributions/struct.DistIter.html" title="struct rand::distributions::DistIter">DistIter</a><D, R, T></span><code class="content"><span class="where fmt-newline">impl<D, R, T> <a class="trait" href="https://doc.rust-lang.org/1.66.0/core/iter/traits/iterator/trait.Iterator.html" title="trait core::iter::traits::iterator::Iterator">Iterator</a> for <a class="struct" href="distributions/struct.DistIter.html" title="struct rand::distributions::DistIter">DistIter</a><D, R, T><span class="where fmt-newline">where<br> D: <a class="trait" href="distributions/trait.Distribution.html" title="trait rand::distributions::Distribution">Distribution</a><T>,<br> R: <a class="trait" href="trait.Rng.html" title="trait rand::Rng">Rng</a>,</span></span><span class="where fmt-newline"> type <a href="https://doc.rust-lang.org/1.66.0/core/iter/traits/iterator/trait.Iterator.html#associatedtype.Item" class="associatedtype">Item</a> = T;</span></code></span></span></span></span><span class="where fmt-newline">where<br> D: <a class="trait" href="distributions/trait.Distribution.html" title="trait rand::distributions::Distribution">Distribution</a><T>,<br> Self: <a class="trait" href="https://doc.rust-lang.org/1.66.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>,</span></h4></section></summary><div class="docblock"><p>Create an iterator that generates values using the given distribution.</p>
<p>Note that this function takes its arguments by value. This works since
<code>(&mut R): Rng where R: Rng</code> and
<code>(&D): Distribution where D: Distribution</code>,
however borrowing is not automatic hence <code>rng.sample_iter(...)</code> may
need to be replaced with <code>(&mut rng).sample_iter(...)</code>.</p>
<h5 id="example-3"><a href="#example-3">Example</a></h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">use </span>rand::distributions::{Alphanumeric, Uniform, Standard};
<span class="kw">let </span><span class="kw-2">mut </span>rng = thread_rng();
<span class="comment">// Vec of 16 x f32:
</span><span class="kw">let </span>v: Vec<f32> = (<span class="kw-2">&mut </span>rng).sample_iter(Standard).take(<span class="number">16</span>).collect();
<span class="comment">// String:
</span><span class="kw">let </span>s: String = (<span class="kw-2">&mut </span>rng).sample_iter(Alphanumeric)
.take(<span class="number">7</span>)
.map(char::from)
.collect();
<span class="comment">// Combined values
</span><span class="macro">println!</span>(<span class="string">"{:?}"</span>, (<span class="kw-2">&mut </span>rng).sample_iter(Standard).take(<span class="number">5</span>)
.collect::<Vec<(f64, bool)>>());
<span class="comment">// Dice-rolling:
</span><span class="kw">let </span>die_range = Uniform::new_inclusive(<span class="number">1</span>, <span class="number">6</span>);
<span class="kw">let </span><span class="kw-2">mut </span>roll_die = (<span class="kw-2">&mut </span>rng).sample_iter(die_range);
<span class="kw">while </span>roll_die.next().unwrap() != <span class="number">6 </span>{
<span class="macro">println!</span>(<span class="string">"Not a 6; rolling again!"</span>);
}</code></pre></div>
</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.fill" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#218-220">source</a><h4 class="code-header">fn <a href="#method.fill" class="fnname">fill</a><T: <a class="trait" href="trait.Fill.html" title="trait rand::Fill">Fill</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.66.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, dest: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.reference.html">&mut </a>T)</h4></section></summary><div class="docblock"><p>Fill any type implementing <a href="trait.Fill.html" title="Fill"><code>Fill</code></a> with random data</p>
<p>The distribution is expected to be uniform with portable results, but
this cannot be guaranteed for third-party implementations.</p>
<p>This is identical to <a href="trait.Rng.html#method.try_fill"><code>try_fill</code></a> except that it panics on error.</p>
<h5 id="example-4"><a href="#example-4">Example</a></h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">let </span><span class="kw-2">mut </span>arr = [<span class="number">0i8</span>; <span class="number">20</span>];
thread_rng().fill(<span class="kw-2">&mut </span>arr[..]);</code></pre></div>
</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.try_fill" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#246-248">source</a><h4 class="code-header">fn <a href="#method.try_fill" class="fnname">try_fill</a><T: <a class="trait" href="trait.Fill.html" title="trait rand::Fill">Fill</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.66.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>>(&mut self, dest: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.reference.html">&mut </a>T) -> <a class="enum" href="https://doc.rust-lang.org/1.66.0/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.unit.html">()</a>, <a class="struct" href="struct.Error.html" title="struct rand::Error">Error</a>></h4></section></summary><div class="docblock"><p>Fill any type implementing <a href="trait.Rng.html#method.fill"><code>Fill</code></a> with random data</p>
<p>The distribution is expected to be uniform with portable results, but
this cannot be guaranteed for third-party implementations.</p>
<p>This is identical to <a href="trait.Rng.html#method.fill"><code>fill</code></a> except that it forwards errors.</p>
<h5 id="example-5"><a href="#example-5">Example</a></h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">let </span><span class="kw-2">mut </span>arr = [<span class="number">0u64</span>; <span class="number">4</span>];
thread_rng().try_fill(<span class="kw-2">&mut </span>arr[..])<span class="question-mark">?</span>;
</code></pre></div>
</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.gen_bool" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#270-273">source</a><h4 class="code-header">fn <a href="#method.gen_bool" class="fnname">gen_bool</a>(&mut self, p: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.f64.html">f64</a>) -> <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.bool.html">bool</a></h4></section></summary><div class="docblock"><p>Return a bool with a probability <code>p</code> of being true.</p>
<p>See also the <a href="distributions/struct.Bernoulli.html"><code>Bernoulli</code></a> distribution, which may be faster if
sampling from the same probability repeatedly.</p>
<h5 id="example-6"><a href="#example-6">Example</a></h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">let </span><span class="kw-2">mut </span>rng = thread_rng();
<span class="macro">println!</span>(<span class="string">"{}"</span>, rng.gen_bool(<span class="number">1.0 </span>/ <span class="number">3.0</span>));</code></pre></div>
<h5 id="panics-1"><a href="#panics-1">Panics</a></h5>
<p>If <code>p < 0</code> or <code>p > 1</code>.</p>
</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.gen_ratio" class="method has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#299-302">source</a><h4 class="code-header">fn <a href="#method.gen_ratio" class="fnname">gen_ratio</a>(&mut self, numerator: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.u32.html">u32</a>, denominator: <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.u32.html">u32</a>) -> <a class="primitive" href="https://doc.rust-lang.org/1.66.0/std/primitive.bool.html">bool</a></h4></section></summary><div class="docblock"><p>Return a bool with a probability of <code>numerator/denominator</code> of being
true. I.e. <code>gen_ratio(2, 3)</code> has chance of 2 in 3, or about 67%, of
returning true. If <code>numerator == denominator</code>, then the returned value
is guaranteed to be <code>true</code>. If <code>numerator == 0</code>, then the returned
value is guaranteed to be <code>false</code>.</p>
<p>See also the <a href="distributions/struct.Bernoulli.html"><code>Bernoulli</code></a> distribution, which may be faster if
sampling from the same <code>numerator</code> and <code>denominator</code> repeatedly.</p>
<h5 id="panics-2"><a href="#panics-2">Panics</a></h5>
<p>If <code>denominator == 0</code> or <code>numerator > denominator</code>.</p>
<h5 id="example-7"><a href="#example-7">Example</a></h5>
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rand::{thread_rng, Rng};
<span class="kw">let </span><span class="kw-2">mut </span>rng = thread_rng();
<span class="macro">println!</span>(<span class="string">"{}"</span>, rng.gen_ratio(<span class="number">2</span>, <span class="number">3</span>));</code></pre></div>
</div></details></div><h2 id="implementors" class="small-section-header">Implementors<a href="#implementors" class="anchor"></a></h2><div id="implementors-list"><section id="impl-Rng-for-R" class="impl has-srclink"><a class="srclink rightside" href="../src/rand/rng.rs.html#305">source</a><a href="#impl-Rng-for-R" class="anchor"></a><h3 class="code-header">impl<R: <a class="trait" href="trait.RngCore.html" title="trait rand::RngCore">RngCore</a> + ?<a class="trait" href="https://doc.rust-lang.org/1.66.0/core/marker/trait.Sized.html" title="trait core::marker::Sized">Sized</a>> <a class="trait" href="trait.Rng.html" title="trait rand::Rng">Rng</a> for R</h3></section></div><script src="../implementors/rand/rng/trait.Rng.js" async></script></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="rand" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0 (69f9c33d7 2022-12-12) (Arch Linux rust 1:1.66.0-1)" ></div></body></html>
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