80 lines
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80 lines
9.9 KiB
HTML
<!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."><title>slab - Rust</title><script>if(window.location.protocol!=="file:")document.head.insertAdjacentHTML("beforeend","SourceSerif4-Regular-6b053e98.ttf.woff2,FiraSans-Italic-81dc35de.woff2,FiraSans-Regular-0fe48ade.woff2,FiraSans-MediumItalic-ccf7e434.woff2,FiraSans-Medium-e1aa3f0a.woff2,SourceCodePro-Regular-8badfe75.ttf.woff2,SourceCodePro-Semibold-aa29a496.ttf.woff2".split(",").map(f=>`<link rel="preload" as="font" type="font/woff2"href="../static.files/${f}">`).join(""))</script><link rel="stylesheet" href="../static.files/normalize-9960930a.css"><link rel="stylesheet" href="../static.files/rustdoc-ca0dd0c4.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="slab" data-themes="" data-resource-suffix="" data-rustdoc-version="1.93.1 (01f6ddf75 2026-02-11) (Arch Linux rust 1:1.93.1-1)" data-channel="1.93.1" data-search-js="search-9e2438ea.js" data-stringdex-js="stringdex-a3946164.js" data-settings-js="settings-c38705f0.js" ><script src="../static.files/storage-e2aeef58.js"></script><script defer src="../crates.js"></script><script defer src="../static.files/main-a410ff4d.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-263c88ec.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-eab170b8.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-044be391.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]--><rustdoc-topbar><h2><a href="#">Crate slab</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../slab/index.html">slab</a><span class="version">0.4.12</span></h2></div><div class="sidebar-elems"><ul class="block"><li><a id="all-types" href="all.html">All Items</a></li></ul><section id="rustdoc-toc"><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#performance-notes" title="Performance notes">Performance notes</a></li><li><a href="#examples" title="Examples">Examples</a></li><li><a href="#capacity-and-reallocation" title="Capacity and reallocation">Capacity and reallocation</a></li><li><a href="#implementation" title="Implementation">Implementation</a></li></ul><h3><a href="#structs">Crate Items</a></h3><ul class="block"><li><a href="#structs" title="Structs">Structs</a></li><li><a href="#enums" title="Enums">Enums</a></li></ul></section><div id="rustdoc-modnav"></div></div></nav><div class="sidebar-resizer" title="Drag to resize sidebar"></div><main><div class="width-limiter"><section id="main-content" class="content"><div class="main-heading"><h1>Crate <span>slab</span> <button id="copy-path" title="Copy item path to clipboard">Copy item path</button></h1><rustdoc-toolbar></rustdoc-toolbar><span class="sub-heading"><a class="src" href="../src/slab/lib.rs.html#1-1653">Source</a> </span></div><details class="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>
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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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<h2 id="performance-notes"><a class="doc-anchor" href="#performance-notes">§</a>Performance notes</h2>
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<p>Methods that remove values and return them, such as <a href="struct.Slab.html#method.remove" title="method slab::Slab::remove"><code>Slab::remove</code></a> and
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<a href="struct.Slab.html#method.try_remove" title="method slab::Slab::try_remove"><code>Slab::try_remove</code></a>, might copy the removed values to the stack even if
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their return values are unused. For types that don’t have drop glue, the
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compiler can usually elide these copies.</p>
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<h2 id="examples"><a class="doc-anchor" href="#examples">§</a>Examples</h2>
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<p>Basic storing and retrieval.</p>
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<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();
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<span class="kw">let </span>hello = slab.insert(<span class="string">"hello"</span>);
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<span class="kw">let </span>world = slab.insert(<span class="string">"world"</span>);
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<span class="macro">assert_eq!</span>(slab[hello], <span class="string">"hello"</span>);
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<span class="macro">assert_eq!</span>(slab[world], <span class="string">"world"</span>);
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slab[world] = <span class="string">"earth"</span>;
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<span class="macro">assert_eq!</span>(slab[world], <span class="string">"earth"</span>);</code></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"><code><span class="kw">let </span><span class="kw-2">mut </span>slab = Slab::new();
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<span class="kw">let </span>hello = {
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<span class="kw">let </span>entry = slab.vacant_entry();
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<span class="kw">let </span>key = entry.key();
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entry.insert((key, <span class="string">"hello"</span>));
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key
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};
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<span class="macro">assert_eq!</span>(hello, slab[hello].<span class="number">0</span>);
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<span class="macro">assert_eq!</span>(<span class="string">"hello"</span>, slab[hello].<span class="number">1</span>);</code></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"><code><span class="kw">let </span><span class="kw-2">mut </span>slab = Slab::with_capacity(<span class="number">1024</span>);
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<span class="comment">// ... use the slab
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</span><span class="kw">if </span>slab.len() == slab.capacity() {
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<span class="macro">panic!</span>(<span class="string">"slab full"</span>);
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}
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slab.insert(<span class="string">"the slab is not at capacity yet"</span>);</code></pre></div><h2 id="capacity-and-reallocation"><a class="doc-anchor" href="#capacity-and-reallocation">§</a>Capacity and reallocation</h2>
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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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<h2 id="implementation"><a class="doc-anchor" href="#implementation">§</a>Implementation</h2>
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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></details><h2 id="structs" class="section-header">Structs<a href="#structs" class="anchor">§</a></h2><dl class="item-table"><dt><a class="struct" href="struct.Drain.html" title="struct slab::Drain">Drain</a></dt><dd>A draining iterator for <code>Slab</code></dd><dt><a class="struct" href="struct.IntoIter.html" title="struct slab::IntoIter">Into<wbr>Iter</a></dt><dd>A consuming iterator over the values stored in a <code>Slab</code></dd><dt><a class="struct" href="struct.Iter.html" title="struct slab::Iter">Iter</a></dt><dd>An iterator over the values stored in the <code>Slab</code></dd><dt><a class="struct" href="struct.IterMut.html" title="struct slab::IterMut">IterMut</a></dt><dd>A mutable iterator over the values stored in the <code>Slab</code></dd><dt><a class="struct" href="struct.Slab.html" title="struct slab::Slab">Slab</a></dt><dd>Pre-allocated storage for a uniform data type</dd><dt><a class="struct" href="struct.VacantEntry.html" title="struct slab::VacantEntry">Vacant<wbr>Entry</a></dt><dd>A handle to a vacant entry in a <code>Slab</code>.</dd></dl><h2 id="enums" class="section-header">Enums<a href="#enums" class="anchor">§</a></h2><dl class="item-table"><dt><a class="enum" href="enum.GetDisjointMutError.html" title="enum slab::GetDisjointMutError">GetDisjoint<wbr>MutError</a></dt><dd>The error type returned by <a href="struct.Slab.html#method.get_disjoint_mut" title="method slab::Slab::get_disjoint_mut"><code>Slab::get_disjoint_mut</code></a>.</dd></dl></section></div></main></body></html> |