| <!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="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/regex-syntax-0.7.2/src/hir/visitor.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>visitor.rs - source</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="../../../source-script.js"></script><script defer src="../../../source-files.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 source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../regex_syntax/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../regex_syntax/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><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="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use </span>alloc::{vec, vec::Vec}; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::hir::{<span class="self">self</span>, Hir, HirKind}; |
| |
| <span class="doccomment">/// A trait for visiting the high-level IR (HIR) in depth first order. |
| /// |
| /// The principle aim of this trait is to enable callers to perform case |
| /// analysis on a high-level intermediate representation of a regular |
| /// expression without necessarily using recursion. In particular, this permits |
| /// callers to do case analysis with constant stack usage, which can be |
| /// important since the size of an HIR may be proportional to end user input. |
| /// |
| /// Typical usage of this trait involves providing an implementation and then |
| /// running it using the [`visit`] function. |
| </span><span class="kw">pub trait </span>Visitor { |
| <span class="doccomment">/// The result of visiting an HIR. |
| </span><span class="kw">type </span>Output; |
| <span class="doccomment">/// An error that visiting an HIR might return. |
| </span><span class="kw">type </span><span class="prelude-val">Err</span>; |
| |
| <span class="doccomment">/// All implementors of `Visitor` must provide a `finish` method, which |
| /// yields the result of visiting the HIR or an error. |
| </span><span class="kw">fn </span>finish(<span class="self">self</span>) -> <span class="prelude-ty">Result</span><<span class="self">Self</span>::Output, <span class="self">Self</span>::Err>; |
| |
| <span class="doccomment">/// This method is called before beginning traversal of the HIR. |
| </span><span class="kw">fn </span>start(<span class="kw-2">&mut </span><span class="self">self</span>) {} |
| |
| <span class="doccomment">/// This method is called on an `Hir` before descending into child `Hir` |
| /// nodes. |
| </span><span class="kw">fn </span>visit_pre(<span class="kw-2">&mut </span><span class="self">self</span>, _hir: <span class="kw-2">&</span>Hir) -> <span class="prelude-ty">Result</span><(), <span class="self">Self</span>::Err> { |
| <span class="prelude-val">Ok</span>(()) |
| } |
| |
| <span class="doccomment">/// This method is called on an `Hir` after descending all of its child |
| /// `Hir` nodes. |
| </span><span class="kw">fn </span>visit_post(<span class="kw-2">&mut </span><span class="self">self</span>, _hir: <span class="kw-2">&</span>Hir) -> <span class="prelude-ty">Result</span><(), <span class="self">Self</span>::Err> { |
| <span class="prelude-val">Ok</span>(()) |
| } |
| |
| <span class="doccomment">/// This method is called between child nodes of an alternation. |
| </span><span class="kw">fn </span>visit_alternation_in(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Result</span><(), <span class="self">Self</span>::Err> { |
| <span class="prelude-val">Ok</span>(()) |
| } |
| } |
| |
| <span class="doccomment">/// Executes an implementation of `Visitor` in constant stack space. |
| /// |
| /// This function will visit every node in the given `Hir` while calling |
| /// appropriate methods provided by the [`Visitor`] trait. |
| /// |
| /// The primary use case for this method is when one wants to perform case |
| /// analysis over an `Hir` without using a stack size proportional to the depth |
| /// of the `Hir`. Namely, this method will instead use constant stack space, |
| /// but will use heap space proportional to the size of the `Hir`. This may be |
| /// desirable in cases where the size of `Hir` is proportional to end user |
| /// input. |
| /// |
| /// If the visitor returns an error at any point, then visiting is stopped and |
| /// the error is returned. |
| </span><span class="kw">pub fn </span>visit<V: Visitor>(hir: <span class="kw-2">&</span>Hir, visitor: V) -> <span class="prelude-ty">Result</span><V::Output, V::Err> { |
| HeapVisitor::new().visit(hir, visitor) |
| } |
| |
| <span class="doccomment">/// HeapVisitor visits every item in an `Hir` recursively using constant stack |
| /// size and a heap size proportional to the size of the `Hir`. |
| </span><span class="kw">struct </span>HeapVisitor<<span class="lifetime">'a</span>> { |
| <span class="doccomment">/// A stack of `Hir` nodes. This is roughly analogous to the call stack |
| /// used in a typical recursive visitor. |
| </span>stack: Vec<(<span class="kw-2">&</span><span class="lifetime">'a </span>Hir, Frame<<span class="lifetime">'a</span>>)>, |
| } |
| |
| <span class="doccomment">/// Represents a single stack frame while performing structural induction over |
| /// an `Hir`. |
| </span><span class="kw">enum </span>Frame<<span class="lifetime">'a</span>> { |
| <span class="doccomment">/// A stack frame allocated just before descending into a repetition |
| /// operator's child node. |
| </span>Repetition(<span class="kw-2">&</span><span class="lifetime">'a </span>hir::Repetition), |
| <span class="doccomment">/// A stack frame allocated just before descending into a capture's child |
| /// node. |
| </span>Capture(<span class="kw-2">&</span><span class="lifetime">'a </span>hir::Capture), |
| <span class="doccomment">/// The stack frame used while visiting every child node of a concatenation |
| /// of expressions. |
| </span>Concat { |
| <span class="doccomment">/// The child node we are currently visiting. |
| </span>head: <span class="kw-2">&</span><span class="lifetime">'a </span>Hir, |
| <span class="doccomment">/// The remaining child nodes to visit (which may be empty). |
| </span>tail: <span class="kw-2">&</span><span class="lifetime">'a </span>[Hir], |
| }, |
| <span class="doccomment">/// The stack frame used while visiting every child node of an alternation |
| /// of expressions. |
| </span>Alternation { |
| <span class="doccomment">/// The child node we are currently visiting. |
| </span>head: <span class="kw-2">&</span><span class="lifetime">'a </span>Hir, |
| <span class="doccomment">/// The remaining child nodes to visit (which may be empty). |
| </span>tail: <span class="kw-2">&</span><span class="lifetime">'a </span>[Hir], |
| }, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>> HeapVisitor<<span class="lifetime">'a</span>> { |
| <span class="kw">fn </span>new() -> HeapVisitor<<span class="lifetime">'a</span>> { |
| HeapVisitor { stack: <span class="macro">vec!</span>[] } |
| } |
| |
| <span class="kw">fn </span>visit<V: Visitor>( |
| <span class="kw-2">&mut </span><span class="self">self</span>, |
| <span class="kw-2">mut </span>hir: <span class="kw-2">&</span><span class="lifetime">'a </span>Hir, |
| <span class="kw-2">mut </span>visitor: V, |
| ) -> <span class="prelude-ty">Result</span><V::Output, V::Err> { |
| <span class="self">self</span>.stack.clear(); |
| |
| visitor.start(); |
| <span class="kw">loop </span>{ |
| visitor.visit_pre(hir)<span class="question-mark">?</span>; |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(x) = <span class="self">self</span>.induct(hir) { |
| <span class="kw">let </span>child = x.child(); |
| <span class="self">self</span>.stack.push((hir, x)); |
| hir = child; |
| <span class="kw">continue</span>; |
| } |
| <span class="comment">// No induction means we have a base case, so we can post visit |
| // it now. |
| </span>visitor.visit_post(hir)<span class="question-mark">?</span>; |
| |
| <span class="comment">// At this point, we now try to pop our call stack until it is |
| // either empty or we hit another inductive case. |
| </span><span class="kw">loop </span>{ |
| <span class="kw">let </span>(post_hir, frame) = <span class="kw">match </span><span class="self">self</span>.stack.pop() { |
| <span class="prelude-val">None </span>=> <span class="kw">return </span>visitor.finish(), |
| <span class="prelude-val">Some</span>((post_hir, frame)) => (post_hir, frame), |
| }; |
| <span class="comment">// If this is a concat/alternate, then we might have additional |
| // inductive steps to process. |
| </span><span class="kw">if let </span><span class="prelude-val">Some</span>(x) = <span class="self">self</span>.pop(frame) { |
| <span class="kw">if let </span>Frame::Alternation { .. } = x { |
| visitor.visit_alternation_in()<span class="question-mark">?</span>; |
| } |
| hir = x.child(); |
| <span class="self">self</span>.stack.push((post_hir, x)); |
| <span class="kw">break</span>; |
| } |
| <span class="comment">// Otherwise, we've finished visiting all the child nodes for |
| // this HIR, so we can post visit it now. |
| </span>visitor.visit_post(post_hir)<span class="question-mark">?</span>; |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Build a stack frame for the given HIR if one is needed (which occurs if |
| /// and only if there are child nodes in the HIR). Otherwise, return None. |
| </span><span class="kw">fn </span>induct(<span class="kw-2">&mut </span><span class="self">self</span>, hir: <span class="kw-2">&</span><span class="lifetime">'a </span>Hir) -> <span class="prelude-ty">Option</span><Frame<<span class="lifetime">'a</span>>> { |
| <span class="kw">match </span><span class="kw-2">*</span>hir.kind() { |
| HirKind::Repetition(<span class="kw-2">ref </span>x) => <span class="prelude-val">Some</span>(Frame::Repetition(x)), |
| HirKind::Capture(<span class="kw-2">ref </span>x) => <span class="prelude-val">Some</span>(Frame::Capture(x)), |
| HirKind::Concat(<span class="kw-2">ref </span>x) <span class="kw">if </span>x.is_empty() => <span class="prelude-val">None</span>, |
| HirKind::Concat(<span class="kw-2">ref </span>x) => { |
| <span class="prelude-val">Some</span>(Frame::Concat { head: <span class="kw-2">&</span>x[<span class="number">0</span>], tail: <span class="kw-2">&</span>x[<span class="number">1</span>..] }) |
| } |
| HirKind::Alternation(<span class="kw-2">ref </span>x) <span class="kw">if </span>x.is_empty() => <span class="prelude-val">None</span>, |
| HirKind::Alternation(<span class="kw-2">ref </span>x) => { |
| <span class="prelude-val">Some</span>(Frame::Alternation { head: <span class="kw-2">&</span>x[<span class="number">0</span>], tail: <span class="kw-2">&</span>x[<span class="number">1</span>..] }) |
| } |
| <span class="kw">_ </span>=> <span class="prelude-val">None</span>, |
| } |
| } |
| |
| <span class="doccomment">/// Pops the given frame. If the frame has an additional inductive step, |
| /// then return it, otherwise return `None`. |
| </span><span class="kw">fn </span>pop(<span class="kw-2">&</span><span class="self">self</span>, induct: Frame<<span class="lifetime">'a</span>>) -> <span class="prelude-ty">Option</span><Frame<<span class="lifetime">'a</span>>> { |
| <span class="kw">match </span>induct { |
| Frame::Repetition(<span class="kw">_</span>) => <span class="prelude-val">None</span>, |
| Frame::Capture(<span class="kw">_</span>) => <span class="prelude-val">None</span>, |
| Frame::Concat { tail, .. } => { |
| <span class="kw">if </span>tail.is_empty() { |
| <span class="prelude-val">None |
| </span>} <span class="kw">else </span>{ |
| <span class="prelude-val">Some</span>(Frame::Concat { head: <span class="kw-2">&</span>tail[<span class="number">0</span>], tail: <span class="kw-2">&</span>tail[<span class="number">1</span>..] }) |
| } |
| } |
| Frame::Alternation { tail, .. } => { |
| <span class="kw">if </span>tail.is_empty() { |
| <span class="prelude-val">None |
| </span>} <span class="kw">else </span>{ |
| <span class="prelude-val">Some</span>(Frame::Alternation { |
| head: <span class="kw-2">&</span>tail[<span class="number">0</span>], |
| tail: <span class="kw-2">&</span>tail[<span class="number">1</span>..], |
| }) |
| } |
| } |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>> Frame<<span class="lifetime">'a</span>> { |
| <span class="doccomment">/// Perform the next inductive step on this frame and return the next |
| /// child HIR node to visit. |
| </span><span class="kw">fn </span>child(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span><span class="lifetime">'a </span>Hir { |
| <span class="kw">match </span><span class="kw-2">*</span><span class="self">self </span>{ |
| Frame::Repetition(rep) => <span class="kw-2">&</span>rep.sub, |
| Frame::Capture(capture) => <span class="kw-2">&</span>capture.sub, |
| Frame::Concat { head, .. } => head, |
| Frame::Alternation { head, .. } => head, |
| } |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="regex_syntax" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
