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</a><div class="sidebar-elems"><h2 class="location"><a href="index.html">In 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">
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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#183-186">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><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><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>
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<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
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documentation of the entropy source and <a href="distributions/struct.Standard.html"><code>Standard</code></a> for documentation of
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distributions and type-specific generation.</p>
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<h2 id="provided-implementations"><a href="#provided-implementations">Provided implementations</a></h2>
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<p>The following types have provided implementations that
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generate values with the following ranges and distributions:</p>
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<ul>
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<li>Integers (<code>i32</code>, <code>u32</code>, <code>isize</code>, <code>usize</code>, etc.): Uniformly distributed
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over all values of the type.</li>
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<li><code>char</code>: Uniformly distributed over all Unicode scalar values, i.e. all
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code points in the range <code>0...0x10_FFFF</code>, except for the range
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<code>0xD800...0xDFFF</code> (the surrogate code points). This includes
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unassigned/reserved code points.</li>
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<li><code>bool</code>: Generates <code>false</code> or <code>true</code>, each with probability 0.5.</li>
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<li>Floating point types (<code>f32</code> and <code>f64</code>): Uniformly distributed in the
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half-open range <code>[0, 1)</code>. See notes below.</li>
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<li>Wrapping integers (<code>Wrapping<T></code>), besides the type identical to their
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normal integer variants.</li>
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</ul>
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<p>Also supported is the generation of the following
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compound types where all component types are supported:</p>
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<ul>
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<li>Tuples (up to 12 elements): each element is generated sequentially.</li>
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<li>Arrays (up to 32 elements): each element is generated sequentially;
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see also <a href="trait.Rng.html#method.fill" title="Rng::fill"><code>Rng::fill</code></a> which supports arbitrary array length for integer
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types and tends to be faster for <code>u32</code> and smaller types.</li>
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<li><code>Option<T></code> first generates a <code>bool</code>, and if true generates and returns
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<code>Some(value)</code> where <code>value: T</code>, otherwise returning <code>None</code>.</li>
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</ul>
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<h2 id="examples"><a href="#examples">Examples</a></h2>
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<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>();
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<span class="macro">println!</span>(<span class="string">"{}"</span>, <span class="ident">x</span>);
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<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>();
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<span class="macro">println!</span>(<span class="string">"{}"</span>, <span class="ident">y</span>);
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<span class="kw">if</span> <span class="ident">rand::random</span>() { <span class="comment">// generates a boolean</span>
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<span class="macro">println!</span>(<span class="string">"Better lucky than good!"</span>);
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}</code></pre></div>
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<p>If you’re calling <code>random()</code> in a loop, caching the generator as in the
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following example can increase performance.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">rand::Rng</span>;
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<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>];
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<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>() {
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<span class="kw-2">*</span><span class="ident">x</span> <span class="op">=</span> <span class="ident">rand::random</span>()
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}
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<span class="comment">// can be made faster by caching thread_rng</span>
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<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>();
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<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>() {
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<span class="kw-2">*</span><span class="ident">x</span> <span class="op">=</span> <span class="ident">rng</span>.<span class="ident">gen</span>();
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}</code></pre></div>
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