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</pre><pre class="rust ">
<span class="kw">use</span> <span class="ident">core</span>;
<span class="kw">use</span> <span class="ident">Poll</span>;
<span class="kw">use</span> <span class="ident">stream</span>;
<span class="kw">use</span> <span class="ident">stream</span>::<span class="ident">Stream</span>;
<span class="doccomment">/// A stream which emits single element and then EOF.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This stream will never block and is always ready.</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="attribute">#[<span class="ident">must_use</span> <span class="op">=</span> <span class="string">"streams do nothing unless polled"</span>]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span>(<span class="ident">stream</span>::<span class="ident">Iter</span><span class="op"><</span><span class="ident">core</span>::<span class="ident">iter</span>::<span class="ident">Once</span><span class="op"><</span><span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">>></span><span class="op">></span>);
<span class="doccomment">/// Creates a stream of single element</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```rust</span>
<span class="doccomment">/// use futures::*;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// let mut stream = stream::once::<(), _>(Err(17));</span>
<span class="doccomment">/// assert_eq!(Err(17), stream.poll());</span>
<span class="doccomment">/// assert_eq!(Ok(Async::Ready(None)), stream.poll());</span>
<span class="doccomment">/// ```</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">once</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span>(<span class="ident">item</span>: <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> {
<span class="ident">Once</span>(<span class="ident">stream</span>::<span class="ident">iter</span>(<span class="ident">core</span>::<span class="ident">iter</span>::<span class="ident">once</span>(<span class="ident">item</span>)))
}
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> <span class="ident">Stream</span> <span class="kw">for</span> <span class="ident">Once</span><span class="op"><</span><span class="ident">T</span>, <span class="ident">E</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Item</span> <span class="op">=</span> <span class="ident">T</span>;
<span class="kw">type</span> <span class="ident">Error</span> <span class="op">=</span> <span class="ident">E</span>;
<span class="kw">fn</span> <span class="ident">poll</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">E</span><span class="op">></span> {
<span class="self">self</span>.<span class="number">0</span>.<span class="ident">poll</span>()
}
}
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