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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 `slab` crate."><meta name="keywords" content="rust, rustlang, rust-lang, slab"><title>slab - Rust</title><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="../dark.css"><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script src="../storage.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="shortcut icon" href="../favicon.ico"><style type="text/css">#crate-search{background-image:url("../down-arrow.svg");}</style></head><body class="rustdoc mod"><!--[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">☰</div><a href='../slab/index.html'><div class='logo-container'><img src='../rust-logo.png' alt='logo'></div></a><p class='location'>Crate slab</p><div class="sidebar-elems"><a id='all-types' href='all.html'><p>See all slab's items</p></a><div class="block items"><ul><li><a href="#structs">Structs</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'slab', ty: 'mod', relpath: '../'};</script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../theme.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="../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../src/slab/lib.rs.html#1-977' title='goto source code'>[src]</a></span><span class='in-band'>Crate <a class="mod" href=''>slab</a></span></h1><div class='docblock'><p>Pre-allocated storage for a uniform data type.</p>
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<p><code>Slab</code> provides pre-allocated storage for a single data type. If many values
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of a single type are being allocated, it can be more efficient to
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pre-allocate the necessary storage. Since the size of the type is uniform,
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memory fragmentation can be avoided. Storing, clearing, and lookup
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operations become very cheap.</p>
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<p>While <code>Slab</code> may look like other Rust collections, it is not intended to be
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used as a general purpose collection. The primary difference between <code>Slab</code>
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and <code>Vec</code> is that <code>Slab</code> returns the key when storing the value.</p>
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<p>It is important to note that keys may be reused. In other words, once a
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value associated with a given key is removed from a slab, that key may be
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returned from future calls to <code>insert</code>.</p>
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<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
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<p>Basic storing and retrieval.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">slab</span> <span class="op">=</span> <span class="ident">Slab</span>::<span class="ident">new</span>();
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<span class="kw">let</span> <span class="ident">hello</span> <span class="op">=</span> <span class="ident">slab</span>.<span class="ident">insert</span>(<span class="string">"hello"</span>);
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<span class="kw">let</span> <span class="ident">world</span> <span class="op">=</span> <span class="ident">slab</span>.<span class="ident">insert</span>(<span class="string">"world"</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">slab</span>[<span class="ident">hello</span>], <span class="string">"hello"</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">slab</span>[<span class="ident">world</span>], <span class="string">"world"</span>);
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<span class="ident">slab</span>[<span class="ident">world</span>] <span class="op">=</span> <span class="string">"earth"</span>;
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">slab</span>[<span class="ident">world</span>], <span class="string">"earth"</span>);</pre></div>
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<p>Sometimes it is useful to be able to associate the key with the value being
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inserted in the slab. This can be done with the <code>vacant_entry</code> API as such:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">slab</span> <span class="op">=</span> <span class="ident">Slab</span>::<span class="ident">new</span>();
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<span class="kw">let</span> <span class="ident">hello</span> <span class="op">=</span> {
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<span class="kw">let</span> <span class="ident">entry</span> <span class="op">=</span> <span class="ident">slab</span>.<span class="ident">vacant_entry</span>();
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<span class="kw">let</span> <span class="ident">key</span> <span class="op">=</span> <span class="ident">entry</span>.<span class="ident">key</span>();
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<span class="ident">entry</span>.<span class="ident">insert</span>((<span class="ident">key</span>, <span class="string">"hello"</span>));
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<span class="ident">key</span>
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};
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="ident">hello</span>, <span class="ident">slab</span>[<span class="ident">hello</span>].<span class="number">0</span>);
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<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="string">"hello"</span>, <span class="ident">slab</span>[<span class="ident">hello</span>].<span class="number">1</span>);</pre></div>
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<p>It is generally a good idea to specify the desired capacity of a slab at
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creation time. Note that <code>Slab</code> will grow the internal capacity when
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attempting to insert a new value once the existing capacity has been reached.
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To avoid this, add a check.</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered">
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<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">slab</span> <span class="op">=</span> <span class="ident">Slab</span>::<span class="ident">with_capacity</span>(<span class="number">1024</span>);
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<span class="comment">// ... use the slab</span>
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<span class="kw">if</span> <span class="ident">slab</span>.<span class="ident">len</span>() <span class="op">=</span><span class="op">=</span> <span class="ident">slab</span>.<span class="ident">capacity</span>() {
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<span class="macro">panic</span><span class="macro">!</span>(<span class="string">"slab full"</span>);
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}
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<span class="ident">slab</span>.<span class="ident">insert</span>(<span class="string">"the slab is not at capacity yet"</span>);</pre></div>
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<h1 id="capacity-and-reallocation" class="section-header"><a href="#capacity-and-reallocation">Capacity and reallocation</a></h1>
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<p>The capacity of a slab is the amount of space allocated for any future
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values that will be inserted in the slab. This is not to be confused with
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the <em>length</em> of the slab, which specifies the number of actual values
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currently being inserted. If a slab's length is equal to its capacity, the
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next value inserted into the slab will require growing the slab by
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reallocating.</p>
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<p>For example, a slab with capacity 10 and length 0 would be an empty slab
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with space for 10 more stored values. Storing 10 or fewer elements into the
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slab will not change its capacity or cause reallocation to occur. However,
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if the slab length is increased to 11 (due to another <code>insert</code>), it will
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have to reallocate, which can be slow. For this reason, it is recommended to
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use <a href="struct.Slab.html#with_capacity"><code>Slab::with_capacity</code></a> whenever possible to specify how many values the
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slab is expected to store.</p>
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<h1 id="implementation" class="section-header"><a href="#implementation">Implementation</a></h1>
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<p><code>Slab</code> is backed by a <code>Vec</code> of slots. Each slot is either occupied or
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vacant. <code>Slab</code> maintains a stack of vacant slots using a linked list. To
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find a vacant slot, the stack is popped. When a slot is released, it is
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pushed onto the stack.</p>
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<p>If there are no more available slots in the stack, then <code>Vec::reserve(1)</code> is
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called and a new slot is created.</p>
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</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table><tr class='module-item'><td><a class="struct" href="struct.Drain.html" title='slab::Drain struct'>Drain</a></td><td class='docblock-short'><p>A draining iterator for <code>Slab</code></p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.Iter.html" title='slab::Iter struct'>Iter</a></td><td class='docblock-short'><p>An iterator over the values stored in the <code>Slab</code></p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.IterMut.html" title='slab::IterMut struct'>IterMut</a></td><td class='docblock-short'><p>A mutable iterator over the values stored in the <code>Slab</code></p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.Slab.html" title='slab::Slab struct'>Slab</a></td><td class='docblock-short'><p>Pre-allocated storage for a uniform data type</p>
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</td></tr><tr class='module-item'><td><a class="struct" href="struct.VacantEntry.html" title='slab::VacantEntry struct'>VacantEntry</a></td><td class='docblock-short'><p>A handle to a vacant entry in a <code>Slab</code>.</p>
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</td></tr></table></section><section id="search" class="content hidden"></section><section class="footer"></section><aside id="help" class="hidden"><div><h1 class="hidden">Help</h1><div class="shortcuts"><h2>Keyboard Shortcuts</h2><dl><dt><kbd>?</kbd></dt><dd>Show this help dialog</dd><dt><kbd>S</kbd></dt><dd>Focus the search field</dd><dt><kbd>↑</kbd></dt><dd>Move up in search results</dd><dt><kbd>↓</kbd></dt><dd>Move down in search results</dd><dt><kbd>↹</kbd></dt><dd>Switch tab</dd><dt><kbd>⏎</kbd></dt><dd>Go to active search result</dd><dt><kbd>+</kbd></dt><dd>Expand all sections</dd><dt><kbd>-</kbd></dt><dd>Collapse all sections</dd></dl></div><div class="infos"><h2>Search Tricks</h2><p>Prefix searches with a type followed by a colon (e.g., <code>fn:</code>) to restrict the search to a given type.</p><p>Accepted types are: <code>fn</code>, <code>mod</code>, <code>struct</code>, <code>enum</code>, <code>trait</code>, <code>type</code>, <code>macro</code>, and <code>const</code>.</p><p>Search functions by type signature (e.g., <code>vec -> usize</code> or <code>* -> vec</code>)</p><p>Search multiple things at once by splitting your query with comma (e.g., <code>str,u8</code> or <code>String,struct:Vec,test</code>)</p></div></div></aside><script>window.rootPath = "../";window.currentCrate = "slab";</script><script src="../aliases.js"></script><script src="../main.js"></script><script defer src="../search-index.js"></script></body></html>
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