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120 lines
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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="Wrap a line of text at a given width."><meta name="keywords" content="rust, rustlang, rust-lang, wrap"><title>wrap in textwrap - Rust</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" type="text/css" href="../normalize.css"><link rel="stylesheet" type="text/css" href="../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../ayu.css" disabled><link rel="stylesheet" type="text/css" href="../dark.css" disabled><link rel="stylesheet" type="text/css" href="../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../storage.js"></script><script src="../crates.js"></script><script defer src="../main.js"></script>
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<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 fn"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu" role="button">☰</div><a class="sidebar-logo" href="../textwrap/index.html"><div class="logo-container"><img class="rust-logo" src="../rust-logo.png" alt="logo"></div>
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</a><div class="sidebar-elems"><h2 class="location">Other items in<br><a href="index.html">textwrap</a></h2><div id="sidebar-vars" data-name="wrap" data-ty="fn" data-relpath=""></div><script defer src="sidebar-items.js"></script></div></nav><main><div class="width-limiter"><div class="sub-container"><a class="sub-logo-container" href="../textwrap/index.html"><img class="rust-logo" src="../rust-logo.png" alt="logo"></a><nav class="sub"><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!" aria-haspopup="menu" title="themes"><img width="18" height="18" alt="Pick another theme!" src="../brush.svg"></button><div id="theme-choices" role="menu"></div></div><form class="search-form"><div class="search-container"><div><select id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><button type="button" id="help-button" title="help">?</button><a id="settings-menu" href="../settings.html" title="settings"><img width="18" height="18" alt="Change settings" src="../wheel.svg"></a></div></form></nav></div><section id="main-content" class="content"><h1 class="fqn"><span class="in-band">Function <a href="index.html">textwrap</a>::<wbr><a class="fn" href="#">wrap</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../clipboard.svg" width="19" height="18" alt="Copy item path"></button></span><span class="out-of-band"><span id="render-detail"><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span><a class="srclink" href="../src/textwrap/lib.rs.html#904-987" title="goto source code">[src]</a></span></h1><div class="docblock item-decl"><pre class="rust fn"><code>pub fn wrap<'a, Opt>(text: &<a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.str.html">str</a>, width_or_options: Opt) -> <a class="struct" href="https://doc.rust-lang.org/1.59.0/alloc/vec/struct.Vec.html" title="struct alloc::vec::Vec">Vec</a><<a class="enum" href="https://doc.rust-lang.org/1.59.0/alloc/borrow/enum.Cow.html" title="enum alloc::borrow::Cow">Cow</a><'_, <a class="primitive" href="https://doc.rust-lang.org/1.59.0/std/primitive.str.html">str</a>>> <span class="where fmt-newline">where<br> Opt: <a class="trait" href="https://doc.rust-lang.org/1.59.0/core/convert/trait.Into.html" title="trait core::convert::Into">Into</a><<a class="struct" href="struct.Options.html" title="struct textwrap::Options">Options</a><'a>>, </span></code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Wrap a line of text at a given width.</p>
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<p>The result is a vector of lines, each line is of type <a href="https://doc.rust-lang.org/1.59.0/alloc/borrow/enum.Cow.html"><code>Cow<'_, str></code></a>, which means that the line will borrow from the input
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<code>&str</code> if possible. The lines do not have trailing whitespace,
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including a final <code>'\n'</code>. Please use the <a href="fn.fill.html" title="fill"><code>fill</code></a> function if you
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need a <a href="https://doc.rust-lang.org/1.59.0/alloc/string/struct.String.html" title="String"><code>String</code></a> instead.</p>
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<p>The easiest way to use this function is to pass an integer for
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<code>width_or_options</code>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">textwrap::wrap</span>;
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<span class="kw">let</span> <span class="ident">lines</span> <span class="op">=</span> <span class="ident">wrap</span>(<span class="string">"Memory safety without garbage collection."</span>, <span class="number">15</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">lines</span>, <span class="kw-2">&</span>[
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<span class="string">"Memory safety"</span>,
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<span class="string">"without garbage"</span>,
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<span class="string">"collection."</span>,
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]);</code></pre></div>
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<p>If you need to customize the wrapping, you can pass an <a href="struct.Options.html" title="Options"><code>Options</code></a>
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instead of an <code>usize</code>:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">textwrap</span>::{<span class="ident">wrap</span>, <span class="ident">Options</span>};
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<span class="kw">let</span> <span class="ident">options</span> <span class="op">=</span> <span class="ident">Options::new</span>(<span class="number">15</span>)
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.<span class="ident">initial_indent</span>(<span class="string">"- "</span>)
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.<span class="ident">subsequent_indent</span>(<span class="string">" "</span>);
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<span class="kw">let</span> <span class="ident">lines</span> <span class="op">=</span> <span class="ident">wrap</span>(<span class="string">"Memory safety without garbage collection."</span>, <span class="kw-2">&</span><span class="ident">options</span>);
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<span class="macro">assert_eq!</span>(<span class="ident">lines</span>, <span class="kw-2">&</span>[
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<span class="string">"- Memory safety"</span>,
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<span class="string">" without"</span>,
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<span class="string">" garbage"</span>,
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<span class="string">" collection."</span>,
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]);</code></pre></div>
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<h2 id="optimal-fit-wrapping" class="section-header"><a href="#optimal-fit-wrapping">Optimal-Fit Wrapping</a></h2>
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<p>By default, <code>wrap</code> will try to ensure an even right margin by
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finding breaks which avoid short lines. We call this an
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“optimal-fit algorithm” since the line breaks are computed by
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considering all possible line breaks. The alternative is a
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“first-fit algorithm” which simply accumulates words until they no
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longer fit on the line.</p>
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<p>As an example, using the first-fit algorithm to wrap the famous
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Hamlet quote “To be, or not to be: that is the question” in a
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narrow column with room for only 10 characters looks like this:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="ident">To</span> <span class="ident">be</span>, <span class="ident">or</span>
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<span class="ident">not</span> <span class="ident">to</span> <span class="ident">be</span>:
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<span class="ident">that</span> <span class="ident">is</span>
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<span class="ident">the</span>
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<span class="ident">question</span></code></pre></div>
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<p>Notice how the second to last line is quite narrow because
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“question” was too large to fit? The greedy first-fit algorithm
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doesn’t look ahead, so it has no other option than to put
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“question” onto its own line.</p>
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<p>With the optimal-fit wrapping algorithm, the previous lines are
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shortened slightly in order to make the word “is” go into the
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second last line:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="ident">To</span> <span class="ident">be</span>,
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<span class="ident">or</span> <span class="ident">not</span> <span class="ident">to</span>
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<span class="ident">be</span>: <span class="ident">that</span>
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<span class="ident">is</span> <span class="ident">the</span>
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<span class="ident">question</span></code></pre></div>
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<p>Please see <a href="wrap_algorithms/enum.WrapAlgorithm.html" title="WrapAlgorithm"><code>WrapAlgorithm</code></a> for details on the choices.</p>
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<h2 id="examples" class="section-header"><a href="#examples">Examples</a></h2>
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<p>The returned iterator yields lines of type <code>Cow<'_, str></code>. If
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possible, the wrapped lines will borrow from the input string. As
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an example, a hanging indentation, the first line can borrow from
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the input, but the subsequent lines become owned strings:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">std::borrow::Cow</span>::{<span class="ident">Borrowed</span>, <span class="ident">Owned</span>};
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<span class="kw">use</span> <span class="ident">textwrap</span>::{<span class="ident">wrap</span>, <span class="ident">Options</span>};
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<span class="kw">let</span> <span class="ident">options</span> <span class="op">=</span> <span class="ident">Options::new</span>(<span class="number">15</span>).<span class="ident">subsequent_indent</span>(<span class="string">"...."</span>);
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<span class="kw">let</span> <span class="ident">lines</span> <span class="op">=</span> <span class="ident">wrap</span>(<span class="string">"Wrapping text all day long."</span>, <span class="kw-2">&</span><span class="ident">options</span>);
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<span class="kw">let</span> <span class="ident">annotated</span> <span class="op">=</span> <span class="ident">lines</span>
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.<span class="ident">iter</span>()
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.<span class="ident">map</span>(<span class="op">|</span><span class="ident">line</span><span class="op">|</span> <span class="kw">match</span> <span class="ident">line</span> {
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<span class="ident">Borrowed</span>(<span class="ident">text</span>) => <span class="macro">format!</span>(<span class="string">"[Borrowed] {}"</span>, <span class="ident">text</span>),
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<span class="ident">Owned</span>(<span class="ident">text</span>) => <span class="macro">format!</span>(<span class="string">"[Owned] {}"</span>, <span class="ident">text</span>),
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})
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.<span class="ident">collect</span>::<span class="op"><</span><span class="ident">Vec</span><span class="op"><</span><span class="kw">_</span><span class="op">></span><span class="op">></span>();
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<span class="macro">assert_eq!</span>(
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<span class="ident">annotated</span>,
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<span class="kw-2">&</span>[
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<span class="string">"[Borrowed] Wrapping text"</span>,
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<span class="string">"[Owned] ....all day"</span>,
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<span class="string">"[Owned] ....long."</span>,
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]
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);</code></pre></div>
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<h3 id="leading-and-trailing-whitespace" class="section-header"><a href="#leading-and-trailing-whitespace">Leading and Trailing Whitespace</a></h3>
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<p>As a rule, leading whitespace (indentation) is preserved and
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trailing whitespace is discarded.</p>
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<p>In more details, when wrapping words into lines, words are found
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by splitting the input text on space characters. One or more
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spaces (shown here as “␣”) are attached to the end of each word:</p>
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<div class="example-wrap"><pre class="language-text"><code>"Foo␣␣␣bar␣baz" -> ["Foo␣␣␣", "bar␣", "baz"]</code></pre></div>
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<p>These words are then put into lines. The interword whitespace is
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preserved, unless the lines are wrapped so that the <code>"Foo␣␣␣"</code>
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word falls at the end of a line:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">textwrap::wrap</span>;
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<span class="macro">assert_eq!</span>(<span class="ident">wrap</span>(<span class="string">"Foo bar baz"</span>, <span class="number">10</span>), <span class="macro">vec!</span>[<span class="string">"Foo bar"</span>, <span class="string">"baz"</span>]);
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<span class="macro">assert_eq!</span>(<span class="ident">wrap</span>(<span class="string">"Foo bar baz"</span>, <span class="number">8</span>), <span class="macro">vec!</span>[<span class="string">"Foo"</span>, <span class="string">"bar baz"</span>]);</code></pre></div>
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<p>Notice how the trailing whitespace is removed in both case: in the
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first example, <code>"bar␣"</code> becomes <code>"bar"</code> and in the second case
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<code>"Foo␣␣␣"</code> becomes <code>"Foo"</code>.</p>
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<p>Leading whitespace is preserved when the following word fits on
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the first line. To understand this, consider how words are found
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in a text with leading spaces:</p>
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<div class="example-wrap"><pre class="language-text"><code>"␣␣foo␣bar" -> ["␣␣", "foo␣", "bar"]</code></pre></div>
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<p>When put into lines, the indentation is preserved if <code>"foo"</code> fits
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on the first line, otherwise you end up with an empty line:</p>
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<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use</span> <span class="ident">textwrap::wrap</span>;
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<span class="macro">assert_eq!</span>(<span class="ident">wrap</span>(<span class="string">" foo bar"</span>, <span class="number">8</span>), <span class="macro">vec!</span>[<span class="string">" foo"</span>, <span class="string">"bar"</span>]);
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<span class="macro">assert_eq!</span>(<span class="ident">wrap</span>(<span class="string">" foo bar"</span>, <span class="number">4</span>), <span class="macro">vec!</span>[<span class="string">""</span>, <span class="string">"foo"</span>, <span class="string">"bar"</span>]);</code></pre></div>
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