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<p class='location'><a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>iter</a></p><script>window.sidebarCurrent = {name: 'once', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script>
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<h1 class='fqn'><span class='in-band'>Function <a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>iter</a>::<wbr><a class='fn' href=''>once</a></span><span class='out-of-band'><span id='render-detail'>
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[<span class='inner'>−</span>]
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</span><a id='src-29275' class='srclink' href='https://doc.rust-lang.org/nightly/core/iter/sources/fn.once.html?gotosrc=29275' title='goto source code'>[src]</a></span></h1>
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<pre class='rust fn'>pub fn once<T>(value: T) -> <a class='struct' href='../../../bitflags/__core/iter/struct.Once.html' title='bitflags::__core::iter::Once'>Once</a><T></pre><span class="since">1.2.0</span><div class='docblock'><p>Creates an iterator that yields an element exactly once.</p>
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<p>This is commonly used to adapt a single value into a <a href="trait.Iterator.html#method.chain"><code>chain()</code></a> of other
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kinds of iteration. Maybe you have an iterator that covers almost
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everything, but you need an extra special case. Maybe you have a function
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which works on iterators, but you only need to process one value.</p>
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<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
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<p>Basic usage:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>iter</span>;
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<span class='comment'>// one is the loneliest number</span>
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<span class='kw'>let</span> <span class='kw-2'>mut</span> <span class='ident'>one</span> <span class='op'>=</span> <span class='ident'>iter</span>::<span class='ident'>once</span>(<span class='number'>1</span>);
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<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='prelude-val'>Some</span>(<span class='number'>1</span>), <span class='ident'>one</span>.<span class='ident'>next</span>());
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<span class='comment'>// just one, that's all we get</span>
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<span class='macro'>assert_eq</span><span class='macro'>!</span>(<span class='prelude-val'>None</span>, <span class='ident'>one</span>.<span class='ident'>next</span>());</pre>
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<p>Chaining together with another iterator. Let's say that we want to iterate
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over each file of the <code>.foo</code> directory, but also a configuration file,
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<code>.foorc</code>:</p>
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<pre class='rust rust-example-rendered'>
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>iter</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>fs</span>;
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<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>path</span>::<span class='ident'>PathBuf</span>;
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<span class='kw'>let</span> <span class='ident'>dirs</span> <span class='op'>=</span> <span class='ident'>fs</span>::<span class='ident'>read_dir</span>(<span class='string'>".foo"</span>).<span class='ident'>unwrap</span>();
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<span class='comment'>// we need to convert from an iterator of DirEntry-s to an iterator of</span>
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<span class='comment'>// PathBufs, so we use map</span>
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<span class='kw'>let</span> <span class='ident'>dirs</span> <span class='op'>=</span> <span class='ident'>dirs</span>.<span class='ident'>map</span>(<span class='op'>|</span><span class='ident'>file</span><span class='op'>|</span> <span class='ident'>file</span>.<span class='ident'>unwrap</span>().<span class='ident'>path</span>());
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<span class='comment'>// now, our iterator just for our config file</span>
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<span class='kw'>let</span> <span class='ident'>config</span> <span class='op'>=</span> <span class='ident'>iter</span>::<span class='ident'>once</span>(<span class='ident'>PathBuf</span>::<span class='ident'>from</span>(<span class='string'>".foorc"</span>));
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<span class='comment'>// chain the two iterators together into one big iterator</span>
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<span class='kw'>let</span> <span class='ident'>files</span> <span class='op'>=</span> <span class='ident'>dirs</span>.<span class='ident'>chain</span>(<span class='ident'>config</span>);
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<span class='comment'>// this will give us all of the files in .foo as well as .foorc</span>
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<span class='kw'>for</span> <span class='ident'>f</span> <span class='kw'>in</span> <span class='ident'>files</span> {
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<span class='macro'>println</span><span class='macro'>!</span>(<span class='string'>"{:?}"</span>, <span class='ident'>f</span>);
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}</pre>
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