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<!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="Create a tree-like prefix parallel iterator from an initial root node. The `children_of` function should take a node and return an iterator over its child nodes. The best parallelization is obtained when the tree is balanced but we should also be able to handle harder cases."><title>walk_tree_prefix in rayon::iter - 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="rayon" 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 fn"><!--[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="#">walk_tree_prefix</a></h2></rustdoc-topbar><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../../rayon/index.html">rayon</a><span class="version">1.11.0</span></h2></div><div class="sidebar-elems"><section id="rustdoc-toc"><h2 class="location"><a href="#">walk_<wbr>tree_<wbr>prefix</a></h2><h3><a href="#">Sections</a></h3><ul class="block top-toc"><li><a href="#ordering" title="Ordering">Ordering</a></li><li><a href="#example" title="Example">Example</a></li><li><a href="#example-1" title="Example">Example</a></li></ul></section><div id="rustdoc-modnav"><h2><a href="index.html">In rayon::<wbr>iter</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">rayon</a>::<wbr><a href="index.html">iter</a></div><h1>Function <span class="fn">walk_<wbr>tree_<wbr>prefix</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/rayon/iter/walk_tree.rs.html#204-214">Source</a> </span></div><pre class="rust item-decl"><code>pub fn walk_tree_prefix<S, B, I>(
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root: S,
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children_of: B,
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) -> <a class="struct" href="struct.WalkTreePrefix.html" title="struct rayon::iter::WalkTreePrefix">WalkTreePrefix</a><S, B><div class="where">where
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S: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a>,
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B: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/ops/function/trait.Fn.html" title="trait core::ops::function::Fn">Fn</a>(<a class="primitive" href="https://doc.rust-lang.org/1.93.1/std/primitive.reference.html">&S</a>) -> I + <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a> + <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/marker/trait.Sync.html" title="trait core::marker::Sync">Sync</a>,
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I: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/iter/traits/collect/trait.IntoIterator.html" title="trait core::iter::traits::collect::IntoIterator">IntoIterator</a><Item = S, IntoIter: <a class="trait" href="https://doc.rust-lang.org/1.93.1/core/iter/traits/double_ended/trait.DoubleEndedIterator.html" title="trait core::iter::traits::double_ended::DoubleEndedIterator">DoubleEndedIterator</a>>,</div></code></pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Create a tree-like prefix parallel iterator from an initial root node.
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The <code>children_of</code> function should take a node and return an iterator over its child nodes.
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The best parallelization is obtained when the tree is balanced
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but we should also be able to handle harder cases.</p>
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<h2 id="ordering"><a class="doc-anchor" href="#ordering">§</a>Ordering</h2>
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<p>This function guarantees a prefix ordering. See also <a href="fn.walk_tree_postfix.html" title="fn rayon::iter::walk_tree_postfix"><code>walk_tree_postfix</code></a>,
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which guarantees a postfix order.
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If you don’t care about ordering, you should use <a href="fn.walk_tree.html" title="fn rayon::iter::walk_tree"><code>walk_tree</code></a>,
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which will use whatever is believed to be fastest.
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For example a perfect binary tree of 7 nodes will reduced in the following order:</p>
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<div class="example-wrap"><pre class="language-text"><code> a
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/ \
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/ \
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b c
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/ \ / \
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d e f g
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reduced as a,b,d,e,c,f,g
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</code></pre></div><h2 id="example"><a class="doc-anchor" href="#example">§</a>Example</h2><div class="example-wrap"><pre class="language-text"><code> 4
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/ \
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/ \
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2 3
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/ \
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1 2</code></pre></div>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rayon::iter::walk_tree_prefix;
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<span class="kw">use </span>rayon::prelude::<span class="kw-2">*</span>;
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<span class="kw">let </span>par_iter = walk_tree_prefix(<span class="number">4</span>, |<span class="kw-2">&</span>e| {
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<span class="kw">if </span>e <= <span class="number">2 </span>{
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Vec::new()
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} <span class="kw">else </span>{
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<span class="macro">vec!</span>[e / <span class="number">2</span>, e / <span class="number">2 </span>+ <span class="number">1</span>]
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}
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});
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<span class="macro">assert_eq!</span>(par_iter.sum::<u32>(), <span class="number">12</span>);</code></pre></div><h2 id="example-1"><a class="doc-anchor" href="#example-1">§</a>Example</h2>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>rayon::prelude::<span class="kw-2">*</span>;
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<span class="kw">use </span>rayon::iter::walk_tree_prefix;
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<span class="kw">struct </span>Node {
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content: u32,
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left: <span class="prelude-ty">Option</span><Box<Node>>,
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right: <span class="prelude-ty">Option</span><Box<Node>>,
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}
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<span class="comment">// Here we loop on the following tree:
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//
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// 10
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// / \
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// / \
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// 3 14
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// \
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// \
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// 18
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</span><span class="kw">let </span>root = Node {
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content: <span class="number">10</span>,
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left: <span class="prelude-val">Some</span>(Box::new(Node {
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content: <span class="number">3</span>,
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left: <span class="prelude-val">None</span>,
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right: <span class="prelude-val">None</span>,
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})),
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right: <span class="prelude-val">Some</span>(Box::new(Node {
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content: <span class="number">14</span>,
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left: <span class="prelude-val">None</span>,
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right: <span class="prelude-val">Some</span>(Box::new(Node {
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content: <span class="number">18</span>,
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left: <span class="prelude-val">None</span>,
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right: <span class="prelude-val">None</span>,
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})),
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})),
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};
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<span class="kw">let </span><span class="kw-2">mut </span>v: Vec<u32> = walk_tree_prefix(<span class="kw-2">&</span>root, |r| {
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r.left
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.as_ref()
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.into_iter()
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.chain(r.right.as_ref())
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.map(|n| <span class="kw-2">&**</span>n)
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})
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.map(|node| node.content)
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.collect();
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<span class="macro">assert_eq!</span>(v, <span class="macro">vec!</span>[<span class="number">10</span>, <span class="number">3</span>, <span class="number">14</span>, <span class="number">18</span>]);</code></pre></div></div></details></section></div></main></body></html> |