<main><divclass="width-limiter"><navclass="sub"><formclass="search-form"><span></span><divid="sidebar-button"tabindex="-1"><ahref="../../regex_syntax/all.html"title="show sidebar"></a></div><inputclass="search-input"name="search"aria-label="Run search in the documentation"autocomplete="off"spellcheck="false"placeholder="Click or press ‘S’ to search, ‘?’ for more options…"type="search"><divid="help-button"tabindex="-1"><ahref="../../help.html"title="help">?</a></div><divid="settings-menu"tabindex="-1"><ahref="../../settings.html"title="settings"><imgwidth="22"height="22"alt="Change settings"src="../../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><sectionid="main-content"class="content"><divclass="main-heading"><h1>Trait <ahref="../index.html">regex_syntax</a>::<wbr><ahref="index.html">ast</a>::<wbr><aclass="trait"href="#">Visitor</a><buttonid="copy-path"title="Copy item path to clipboard"><imgsrc="../../static.files/clipboard-7571035ce49a181d.svg"width="19"height="18"alt="Copy item path"></button></h1><spanclass="out-of-band"><aclass="src"href="../../src/regex_syntax/ast/visitor.rs.html#20-102">source</a> · <buttonid="toggle-all-docs"title="collapse all docs">[<span>−</span>]</button></span></div><preclass="rust item-decl"><code>pub trait Visitor {
type <ahref="#associatedtype.Output"class="associatedtype">Output</a>;
type <ahref="#associatedtype.Err"class="associatedtype">Err</a>;
}</code></pre><detailsclass="toggle top-doc"open><summaryclass="hideme"><span>Expand description</span></summary><divclass="docblock"><p>A trait for visiting an abstract syntax tree (AST) in depth first order.</p>
<p>The principle aim of this trait is to enable callers to perform case
analysis on an abstract syntax tree 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 abstract syntax tree
may be proportional to end user input.</p>
<p>Typical usage of this trait involves providing an implementation and then
running it using the <ahref="fn.visit.html"title="fn regex_syntax::ast::visit"><code>visit</code></a> function.</p>
<p>Note that the abstract syntax tree for a regular expression is quite
complex. Unless you specifically need it, you might be able to use the much
simpler <ahref="../hir/struct.Hir.html"title="struct regex_syntax::hir::Hir">high-level intermediate representation</a> and its
</div></details><h2id="required-associated-types"class="section-header">Required Associated Types<ahref="#required-associated-types"class="anchor">§</a></h2><divclass="methods"><detailsclass="toggle"open><summary><sectionid="associatedtype.Output"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#22">source</a><h4class="code-header">type <ahref="#associatedtype.Output"class="associatedtype">Output</a></h4></section></summary><divclass="docblock"><p>The result of visiting an AST.</p>
</div></details><detailsclass="toggle"open><summary><sectionid="associatedtype.Err"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#24">source</a><h4class="code-header">type <ahref="#associatedtype.Err"class="associatedtype">Err</a></h4></section></summary><divclass="docblock"><p>An error that visiting an AST might return.</p>
</div></details></div><h2id="required-methods"class="section-header">Required Methods<ahref="#required-methods"class="anchor">§</a></h2><divclass="methods"><detailsclass="toggle method-toggle"open><summary><sectionid="tymethod.finish"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#28">source</a><h4class="code-header">fn <ahref="#tymethod.finish"class="fn">finish</a>(self) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Output"title="type regex_syntax::ast::Visitor::Output">Output</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>All implementors of <code>Visitor</code> must provide a <code>finish</code> method, which
yields the result of visiting the AST or an error.</p>
</div></details></div><h2id="provided-methods"class="section-header">Provided Methods<ahref="#provided-methods"class="anchor">§</a></h2><divclass="methods"><detailsclass="toggle method-toggle"open><summary><sectionid="method.start"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#31">source</a><h4class="code-header">fn <ahref="#method.start"class="fn">start</a>(&mut self)</h4></section></summary><divclass="docblock"><p>This method is called before beginning traversal of the AST.</p>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.visit_pre"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#35-37">source</a><h4class="code-header">fn <ahref="#method.visit_pre"class="fn">visit_pre</a>(&mut self, _ast: &<aclass="enum"href="enum.Ast.html"title="enum regex_syntax::ast::Ast">Ast</a>) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called on an <code>Ast</code> before descending into child <code>Ast</code>
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.visit_post"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#41-43">source</a><h4class="code-header">fn <ahref="#method.visit_post"class="fn">visit_post</a>(&mut self, _ast: &<aclass="enum"href="enum.Ast.html"title="enum regex_syntax::ast::Ast">Ast</a>) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called on an <code>Ast</code> after descending all of its child
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.visit_alternation_in"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#47-49">source</a><h4class="code-header">fn <ahref="#method.visit_alternation_in"class="fn">visit_alternation_in</a>(&mut self) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called between child nodes of an
</div></details><detailsclass="toggle method-toggle"open><summary><sectionid="method.visit_concat_in"class="method"><aclass="src rightside"href="../../src/regex_syntax/ast/visitor.rs.html#52-54">source</a><h4class="code-header">fn <ahref="#method.visit_concat_in"class="fn">visit_concat_in</a>(&mut self) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called between child nodes of a concatenation.</p>
) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called on every <ahref="enum.ClassSetItem.html"title="enum regex_syntax::ast::ClassSetItem"><code>ClassSetItem</code></a>
) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called on every <ahref="enum.ClassSetItem.html"title="enum regex_syntax::ast::ClassSetItem"><code>ClassSetItem</code></a>
) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called on every
) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called on every
) -><aclass="enum"href="https://doc.rust-lang.org/1.78.0/core/result/enum.Result.html"title="enum core::result::Result">Result</a><<aclass="primitive"href="https://doc.rust-lang.org/1.78.0/std/primitive.unit.html">()</a>, Self::<aclass="associatedtype"href="trait.Visitor.html#associatedtype.Err"title="type regex_syntax::ast::Visitor::Err">Err</a>></h4></section></summary><divclass="docblock"><p>This method is called between the left hand and right hand child nodes
