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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="API documentation for the Rust `drop` fn in crate `std`."><meta name="keywords" content="rust, rustlang, rust-lang, drop"><title>std::mem::drop - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize1.35.0.css"><link rel="stylesheet" type="text/css" href="../../rustdoc1.35.0.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark1.35.0.css"><link rel="stylesheet" type="text/css" href="../../light1.35.0.css" id="themeStyle"><script src="../../storage1.35.0.js"></script><noscript><link rel="stylesheet" href="../../noscript1.35.0.css"></noscript><link rel="shortcut icon" href="../../favicon1.35.0.ico"><style type="text/css">#crate-search{background-image:url("../../down-arrow1.35.0.svg");}</style></head><body class="rustdoc fn"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">&#9776;</div><a href='../../std/index.html'><img src='../../rust-logo1.35.0.png' alt='logo' width='100'></a><div class="sidebar-elems"><p class='location'><a href='../index.html'>std</a>::<wbr><a href='index.html'>mem</a></p><script>window.sidebarCurrent = {name: 'drop', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush1.35.0.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme1.35.0.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><a id="settings-menu" href="../../settings.html"><img src="../../wheel1.35.0.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>&#x2212;</span>]</a></span><a class='srclink' href='../../src/core/mem.rs.html#777' title='goto source code'>[src]</a></span><span class='in-band'>Function <a href='../index.html'>std</a>::<wbr><a href='index.html'>mem</a>::<wbr><a class="fn" href=''>drop</a></span></h1><pre class='rust fn'>pub fn drop&lt;T&gt;(_x: T)</pre><div class='docblock'><p>Disposes of a value.</p>
<p>This does call the argument's implementation of <a href="../ops/trait.Drop.html"><code>Drop</code></a>.</p>
<p>This effectively does nothing for types which implement <code>Copy</code>, e.g.
integers. Such values are copied and <em>then</em> moved into the function, so the
value persists after this function call.</p>
<p>This function is not magic; it is literally defined as</p>

<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">drop</span><span class="op">&lt;</span><span class="ident">T</span><span class="op">&gt;</span>(<span class="ident">_x</span>: <span class="ident">T</span>) { }<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Apub%20fn%20drop%3CT%3E(_x%3A%20T)%20%7B%20%7D%0A%7D">Run</a></pre></div>
<p>Because <code>_x</code> is moved into the function, it is automatically dropped before
the function returns.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<p>Basic usage:</p>

<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="ident">v</span> <span class="op">=</span> <span class="macro">vec</span><span class="macro">!</span>[<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>];

<span class="ident">drop</span>(<span class="ident">v</span>); <span class="comment">// explicitly drop the vector</span><a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Alet%20v%20%3D%20vec!%5B1%2C%202%2C%203%5D%3B%0A%0Adrop(v)%3B%20%2F%2F%20explicitly%20drop%20the%20vector%0A%7D">Run</a></pre></div>
<p>Since <a href="../../std/cell/struct.RefCell.html"><code>RefCell</code></a> enforces the borrow rules at runtime, <code>drop</code> can
release a <a href="../../std/cell/struct.RefCell.html"><code>RefCell</code></a> borrow:</p>

<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">RefCell</span>;

<span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="ident">RefCell</span>::<span class="ident">new</span>(<span class="number">1</span>);

<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">mutable_borrow</span> <span class="op">=</span> <span class="ident">x</span>.<span class="ident">borrow_mut</span>();
<span class="kw-2">*</span><span class="ident">mutable_borrow</span> <span class="op">=</span> <span class="number">1</span>;

<span class="ident">drop</span>(<span class="ident">mutable_borrow</span>); <span class="comment">// relinquish the mutable borrow on this slot</span>

<span class="kw">let</span> <span class="ident">borrow</span> <span class="op">=</span> <span class="ident">x</span>.<span class="ident">borrow</span>();
<span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;{}&quot;</span>, <span class="kw-2">*</span><span class="ident">borrow</span>);<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Acell%3A%3ARefCell%3B%0A%0Alet%20x%20%3D%20RefCell%3A%3Anew(1)%3B%0A%0Alet%20mut%20mutable_borrow%20%3D%20x.borrow_mut()%3B%0A*mutable_borrow%20%3D%201%3B%0A%0Adrop(mutable_borrow)%3B%20%2F%2F%20relinquish%20the%20mutable%20borrow%20on%20this%20slot%0A%0Alet%20borrow%20%3D%20x.borrow()%3B%0Aprintln!(%22%7B%7D%22%2C%20*borrow)%3B%0A%7D">Run</a></pre></div>
<p>Integers and other types implementing <a href="../../std/marker/trait.Copy.html"><code>Copy</code></a> are unaffected by <code>drop</code>.</p>

<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>)]</span>
<span class="kw">struct</span> <span class="ident">Foo</span>(<span class="ident">u8</span>);

<span class="kw">let</span> <span class="ident">x</span> <span class="op">=</span> <span class="number">1</span>;
<span class="kw">let</span> <span class="ident">y</span> <span class="op">=</span> <span class="ident">Foo</span>(<span class="number">2</span>);
<span class="ident">drop</span>(<span class="ident">x</span>); <span class="comment">// a copy of `x` is moved and dropped</span>
<span class="ident">drop</span>(<span class="ident">y</span>); <span class="comment">// a copy of `y` is moved and dropped</span>

<span class="macro">println</span><span class="macro">!</span>(<span class="string">&quot;x: {}, y: {}&quot;</span>, <span class="ident">x</span>, <span class="ident">y</span>.<span class="number">0</span>); <span class="comment">// still available</span><a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0A%23%5Bderive(Copy%2C%20Clone)%5D%0Astruct%20Foo(u8)%3B%0A%0Alet%20x%20%3D%201%3B%0Alet%20y%20%3D%20Foo(2)%3B%0Adrop(x)%3B%20%2F%2F%20a%20copy%20of%20%60x%60%20is%20moved%20and%20dropped%0Adrop(y)%3B%20%2F%2F%20a%20copy%20of%20%60y%60%20is%20moved%20and%20dropped%0A%0Aprintln!(%22x%3A%20%7B%7D%2C%20y%3A%20%7B%7D%22%2C%20x%2C%20y.0)%3B%20%2F%2F%20still%20available%0A%7D">Run</a></pre></div>
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