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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="Chain zero or more iterators together into one sequence."><title>chain in itertools - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceSerif4-Regular-46f98efaafac5295.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Regular-018c141bf0843ffd.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/FiraSans-Medium-8f9a781e4970d388.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Regular-562dcc5011b6de7d.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../static.files/SourceCodePro-Semibold-d899c5a5c4aeb14a.ttf.woff2"><link rel="stylesheet" href="../static.files/normalize-76eba96aa4d2e634.css"><link rel="stylesheet" href="../static.files/rustdoc-ac92e1bbe349e143.css"><meta name="rustdoc-vars" data-root-path="../" data-static-root-path="../static.files/" data-current-crate="itertools" data-themes="" data-resource-suffix="" data-rustdoc-version="1.76.0 (07dca489a 2024-02-04)" data-channel="1.76.0" data-search-js="search-2b6ce74ff89ae146.js" data-settings-js="settings-4313503d2e1961c2.js" ><script src="../static.files/storage-f2adc0d6ca4d09fb.js"></script><script defer src="sidebar-items.js"></script><script defer src="../static.files/main-305769736d49e732.js"></script><noscript><link rel="stylesheet" href="../static.files/noscript-feafe1bb7466e4bd.css"></noscript><link rel="alternate icon" type="image/png" href="../static.files/favicon-16x16-8b506e7a72182f1c.png"><link rel="alternate icon" type="image/png" href="../static.files/favicon-32x32-422f7d1d52889060.png"><link rel="icon" type="image/svg+xml" href="../static.files/favicon-2c020d218678b618.svg"></head><body class="rustdoc macro"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button></nav><nav class="sidebar"><div class="sidebar-crate"><h2><a href="../itertools/index.html">itertools</a><span class="version">0.12.1</span></h2></div><div class="sidebar-elems"></div></nav><div class="sidebar-resizer"></div>
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<main><div class="width-limiter"><nav class="sub"><form class="search-form"><span></span><div id="sidebar-button" tabindex="-1"><a href="../itertools/all.html" title="show sidebar"></a></div><input class="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"><div id="help-button" tabindex="-1"><a href="../help.html" title="help">?</a></div><div id="settings-menu" tabindex="-1"><a href="../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../static.files/wheel-7b819b6101059cd0.svg"></a></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1>Macro <a href="index.html">itertools</a>::<wbr><a class="macro" href="#">chain</a><button id="copy-path" title="Copy item path to clipboard"><img src="../static.files/clipboard-7571035ce49a181d.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="src" href="../src/itertools/lib.rs.html#379-395">source</a> · <button id="toggle-all-docs" title="collapse all docs">[<span>−</span>]</button></span></div><pre class="rust item-decl"><span class="macro">macro_rules! </span>chain {
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() => { ... };
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(<span class="macro-nonterminal">$first</span>:expr $(, <span class="macro-nonterminal">$rest</span>:expr )* $(,)<span class="question-mark">?</span>) => { ... };
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}</pre><details class="toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p><a href="https://doc.rust-lang.org/1.76.0/core/iter/traits/iterator/trait.Iterator.html#method.chain" title="method core::iter::traits::iterator::Iterator::chain">Chain</a> zero or more iterators together into one sequence.</p>
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<p>The comma-separated arguments must implement <a href="https://doc.rust-lang.org/1.76.0/core/iter/traits/collect/trait.IntoIterator.html" title="trait core::iter::traits::collect::IntoIterator"><code>IntoIterator</code></a>.
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The final argument may be followed by a trailing comma.</p>
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<h2 id="examples"><a href="#examples">Examples</a></h2>
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<p>Empty invocations of <code>chain!</code> expand to an invocation of <a href="https://doc.rust-lang.org/1.76.0/core/iter/sources/empty/fn.empty.html" title="fn core::iter::sources::empty::empty"><code>std::iter::empty</code></a>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::iter;
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<span class="kw">use </span>itertools::chain;
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<span class="kw">let _</span>: iter::Empty<()> = <span class="macro">chain!</span>();
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<span class="kw">let _</span>: iter::Empty<i8> = <span class="macro">chain!</span>();</code></pre></div>
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<p>Invocations of <code>chain!</code> with one argument expand to <a href="https://doc.rust-lang.org/1.76.0/core/iter/traits/collect/trait.IntoIterator.html" title="trait core::iter::traits::collect::IntoIterator"><code>arg.into_iter()</code></a>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::{ops::Range, slice};
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<span class="kw">use </span>itertools::chain;
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<span class="kw">let _</span>: <Range<<span class="kw">_</span>> <span class="kw">as </span>IntoIterator>::IntoIter = <span class="macro">chain!</span>((<span class="number">2</span>..<span class="number">6</span>),); <span class="comment">// trailing comma optional!
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</span><span class="kw">let _</span>: <<span class="kw-2">&</span>[<span class="kw">_</span>] <span class="kw">as </span>IntoIterator>::IntoIter = <span class="macro">chain!</span>(<span class="kw-2">&</span>[<span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>]);</code></pre></div>
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<p>Invocations of <code>chain!</code> with multiple arguments <a href="https://doc.rust-lang.org/1.76.0/core/iter/traits/collect/trait.IntoIterator.html" title="trait core::iter::traits::collect::IntoIterator"><code>.into_iter()</code></a> each
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argument, and then <a href="https://doc.rust-lang.org/1.76.0/core/iter/traits/iterator/trait.Iterator.html#method.chain" title="method core::iter::traits::iterator::Iterator::chain"><code>chain</code></a> them together:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>std::{iter::<span class="kw-2">*</span>, ops::Range, slice};
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<span class="kw">use </span>itertools::{assert_equal, chain};
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<span class="comment">// e.g., this:
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</span><span class="kw">let </span>with_macro: Chain<Chain<Once<<span class="kw">_</span>>, Take<Repeat<<span class="kw">_</span>>>>, slice::Iter<<span class="kw">_</span>>> =
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<span class="macro">chain!</span>[once(<span class="kw-2">&</span><span class="number">0</span>), repeat(<span class="kw-2">&</span><span class="number">1</span>).take(<span class="number">2</span>), <span class="kw-2">&</span>[<span class="number">2</span>, <span class="number">3</span>, <span class="number">5</span>],];
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<span class="comment">// ...is equivalent to this:
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</span><span class="kw">let </span>with_method: Chain<Chain<Once<<span class="kw">_</span>>, Take<Repeat<<span class="kw">_</span>>>>, slice::Iter<<span class="kw">_</span>>> =
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once(<span class="kw-2">&</span><span class="number">0</span>)
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.chain(repeat(<span class="kw-2">&</span><span class="number">1</span>).take(<span class="number">2</span>))
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.chain(<span class="kw-2">&</span>[<span class="number">2</span>, <span class="number">3</span>, <span class="number">5</span>]);
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assert_equal(with_macro, with_method);</code></pre></div>
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</div></details></section></div></main></body></html>
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