36 lines
7.3 KiB
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36 lines
7.3 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="This module provides APIs for dealing with the alphabets of finite state machines."><title>regex_automata::util::alphabet - 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="regex_automata" 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="../sidebar-items.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"><!--[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="#">Module alphabet</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../../regex_automata/index.html">regex_<wbr>automata</a><span class="version">0.4.14</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">Module alphabet</a></h2><h3><a href="#structs">Module Items</a></h3><ul class="block"><li><a href="#structs" title="Structs">Structs</a></li></ul></section><div id="rustdoc-modnav"><h2><a href="../index.html">In regex_<wbr>automata::<wbr>util</a></h2></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"><div class="rustdoc-breadcrumbs"><a href="../../index.html">regex_automata</a>::<wbr><a href="../index.html">util</a></div><h1>Module <span>alphabet</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/regex_automata/util/alphabet.rs.html#1-1139">Source</a> </span></div><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>This module provides APIs for dealing with the alphabets of finite state
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machines.</p>
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<p>There are two principal types in this module, <a href="struct.ByteClasses.html" title="struct regex_automata::util::alphabet::ByteClasses"><code>ByteClasses</code></a> and <a href="struct.Unit.html" title="struct regex_automata::util::alphabet::Unit"><code>Unit</code></a>.
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The former defines the alphabet of a finite state machine while the latter
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represents an element of that alphabet.</p>
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<p>To a first approximation, the alphabet of all automata in this crate is just
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a <code>u8</code>. Namely, every distinct byte value. All 256 of them. In practice, this
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can be quite wasteful when building a transition table for a DFA, since it
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requires storing a state identifier for each element in the alphabet. Instead,
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we collapse the alphabet of an automaton down into equivalence classes, where
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every byte in the same equivalence class never discriminates between a match or
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a non-match from any other byte in the same class. For example, in the regex
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<code>[a-z]+</code>, then you could consider it having an alphabet consisting of two
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equivalence classes: <code>a-z</code> and everything else. In terms of the transitions on
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an automaton, it doesn’t actually require representing every distinct byte.
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Just the equivalence classes.</p>
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<p>The downside of equivalence classes is that, of course, searching a haystack
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deals with individual byte values. Those byte values need to be mapped to
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their corresponding equivalence class. This is what <code>ByteClasses</code> does. In
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practice, doing this for every state transition has negligible impact on modern
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CPUs. Moreover, it helps make more efficient use of the CPU cache by (possibly
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considerably) shrinking the size of the transition table.</p>
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<p>One last hiccup concerns <code>Unit</code>. Namely, because of look-around and how the
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DFAs in this crate work, we need to add a sentinel value to our alphabet
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of equivalence classes that represents the “end” of a search. We call that
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sentinel <a href="struct.Unit.html#method.eoi" title="associated function regex_automata::util::alphabet::Unit::eoi"><code>Unit::eoi</code></a> or “end of input.” Thus, a <code>Unit</code> is either an
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equivalence class corresponding to a set of bytes, or it is a special “end of
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input” sentinel.</p>
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<p>In general, you should not expect to need either of these types unless you’re
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doing lower level shenanigans with DFAs, or even building your own DFAs.
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(Although, you don’t have to use these types to build your own DFAs of course.)
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For example, if you’re walking a DFA’s state graph, it’s probably useful to
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make use of <a href="struct.ByteClasses.html" title="struct regex_automata::util::alphabet::ByteClasses"><code>ByteClasses</code></a> to visit each element in the DFA’s alphabet instead
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of just visiting every distinct <code>u8</code> value. The latter isn’t necessarily wrong,
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but it could be potentially very wasteful.</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.ByteClassElements.html" title="struct regex_automata::util::alphabet::ByteClassElements">Byte<wbr>Class<wbr>Elements</a></dt><dd>An iterator over all elements in an equivalence class.</dd><dt><a class="struct" href="struct.ByteClassIter.html" title="struct regex_automata::util::alphabet::ByteClassIter">Byte<wbr>Class<wbr>Iter</a></dt><dd>An iterator over each equivalence class.</dd><dt><a class="struct" href="struct.ByteClassRepresentatives.html" title="struct regex_automata::util::alphabet::ByteClassRepresentatives">Byte<wbr>Class<wbr>Representatives</a></dt><dd>An iterator over representative bytes from each equivalence class.</dd><dt><a class="struct" href="struct.ByteClasses.html" title="struct regex_automata::util::alphabet::ByteClasses">Byte<wbr>Classes</a></dt><dd>A representation of byte oriented equivalence classes.</dd><dt><a class="struct" href="struct.Unit.html" title="struct regex_automata::util::alphabet::Unit">Unit</a></dt><dd>Unit represents a single unit of haystack for DFA based regex engines.</dd></dl></section></div></main></body></html> |