| <!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="Pre-allocated storage for a uniform data type."><meta name="keywords" content="rust, rustlang, rust-lang, slab"><title>slab - 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="../crates.js"></script><script defer src="../main.js"></script><noscript><link rel="stylesheet" href="../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../favicon.svg"></head><body class="rustdoc mod crate"><!--[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="../slab/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../slab/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Crate slab</a></h2><div class="sidebar-elems"><ul class="block"><li class="version">Version 0.4.8</li><li><a id="all-types" href="all.html">All Items</a></li></ul><section><ul class="block"><li><a href="#structs">Structs</a></li></ul></section></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><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></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Crate <a class="mod" href="#">slab</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/slab/lib.rs.html#1-1571">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Pre-allocated storage for a uniform data type.</p> |
| <p><code>Slab</code> provides pre-allocated storage for a single data type. If many values |
| of a single type are being allocated, it can be more efficient to |
| pre-allocate the necessary storage. Since the size of the type is uniform, |
| memory fragmentation can be avoided. Storing, clearing, and lookup |
| operations become very cheap.</p> |
| <p>While <code>Slab</code> may look like other Rust collections, it is not intended to be |
| used as a general purpose collection. The primary difference between <code>Slab</code> |
| and <code>Vec</code> is that <code>Slab</code> returns the key when storing the value.</p> |
| <p>It is important to note that keys may be reused. In other words, once a |
| value associated with a given key is removed from a slab, that key may be |
| returned from future calls to <code>insert</code>.</p> |
| <h2 id="examples"><a href="#examples">Examples</a></h2> |
| <p>Basic storing and retrieval.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span><span class="kw-2">mut </span>slab = Slab::new(); |
| |
| <span class="kw">let </span>hello = slab.insert(<span class="string">"hello"</span>); |
| <span class="kw">let </span>world = slab.insert(<span class="string">"world"</span>); |
| |
| <span class="macro">assert_eq!</span>(slab[hello], <span class="string">"hello"</span>); |
| <span class="macro">assert_eq!</span>(slab[world], <span class="string">"world"</span>); |
| |
| slab[world] = <span class="string">"earth"</span>; |
| <span class="macro">assert_eq!</span>(slab[world], <span class="string">"earth"</span>);</code></pre></div> |
| <p>Sometimes it is useful to be able to associate the key with the value being |
| inserted in the slab. This can be done with the <code>vacant_entry</code> API as such:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span><span class="kw-2">mut </span>slab = Slab::new(); |
| |
| <span class="kw">let </span>hello = { |
| <span class="kw">let </span>entry = slab.vacant_entry(); |
| <span class="kw">let </span>key = entry.key(); |
| |
| entry.insert((key, <span class="string">"hello"</span>)); |
| key |
| }; |
| |
| <span class="macro">assert_eq!</span>(hello, slab[hello].<span class="number">0</span>); |
| <span class="macro">assert_eq!</span>(<span class="string">"hello"</span>, slab[hello].<span class="number">1</span>);</code></pre></div> |
| <p>It is generally a good idea to specify the desired capacity of a slab at |
| creation time. Note that <code>Slab</code> will grow the internal capacity when |
| attempting to insert a new value once the existing capacity has been reached. |
| To avoid this, add a check.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">let </span><span class="kw-2">mut </span>slab = Slab::with_capacity(<span class="number">1024</span>); |
| |
| <span class="comment">// ... use the slab |
| |
| </span><span class="kw">if </span>slab.len() == slab.capacity() { |
| <span class="macro">panic!</span>(<span class="string">"slab full"</span>); |
| } |
| |
| slab.insert(<span class="string">"the slab is not at capacity yet"</span>);</code></pre></div> |
| <h2 id="capacity-and-reallocation"><a href="#capacity-and-reallocation">Capacity and reallocation</a></h2> |
| <p>The capacity of a slab is the amount of space allocated for any future |
| values that will be inserted in the slab. This is not to be confused with |
| the <em>length</em> of the slab, which specifies the number of actual values |
| currently being inserted. If a slab’s length is equal to its capacity, the |
| next value inserted into the slab will require growing the slab by |
| reallocating.</p> |
| <p>For example, a slab with capacity 10 and length 0 would be an empty slab |
| with space for 10 more stored values. Storing 10 or fewer elements into the |
| slab will not change its capacity or cause reallocation to occur. However, |
| if the slab length is increased to 11 (due to another <code>insert</code>), it will |
| have to reallocate, which can be slow. For this reason, it is recommended to |
| use <a href="struct.Slab.html#with_capacity"><code>Slab::with_capacity</code></a> whenever possible to specify how many values the |
| slab is expected to store.</p> |
| <h2 id="implementation"><a href="#implementation">Implementation</a></h2> |
| <p><code>Slab</code> is backed by a <code>Vec</code> of slots. Each slot is either occupied or |
| vacant. <code>Slab</code> maintains a stack of vacant slots using a linked list. To |
| find a vacant slot, the stack is popped. When a slot is released, it is |
| pushed onto the stack.</p> |
| <p>If there are no more available slots in the stack, then <code>Vec::reserve(1)</code> is |
| called and a new slot is created.</p> |
| </div></details><h2 id="structs" class="small-section-header"><a href="#structs">Structs</a></h2><div class="item-table"><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Drain.html" title="slab::Drain struct">Drain</a></div><div class="item-right docblock-short">A draining iterator for <code>Slab</code></div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.IntoIter.html" title="slab::IntoIter struct">IntoIter</a></div><div class="item-right docblock-short">A consuming iterator over the values stored in a <code>Slab</code></div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Iter.html" title="slab::Iter struct">Iter</a></div><div class="item-right docblock-short">An iterator over the values stored in the <code>Slab</code></div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.IterMut.html" title="slab::IterMut struct">IterMut</a></div><div class="item-right docblock-short">A mutable iterator over the values stored in the <code>Slab</code></div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.Slab.html" title="slab::Slab struct">Slab</a></div><div class="item-right docblock-short">Pre-allocated storage for a uniform data type</div></div><div class="item-row"><div class="item-left module-item"><a class="struct" href="struct.VacantEntry.html" title="slab::VacantEntry struct">VacantEntry</a></div><div class="item-right docblock-short">A handle to a vacant entry in a <code>Slab</code>.</div></div></div></section></div></main><div id="rustdoc-vars" data-root-path="../" data-current-crate="slab" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
