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<h1 class='fqn'><span class='in-band'>Function <a href='../index.html'>futures</a>::<wbr><a href='index.html'>future</a>::<wbr><a class="fn" href=''>loop_fn</a></span><span class='out-of-band'><span id='render-detail'>
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               </span><a class='srclink' href='../../src/futures/future/loop_fn.rs.html#74-82' title='goto source code'>[src]</a></span></h1>
<pre class='rust fn'>pub fn loop_fn&lt;S, T, A, F&gt;(initial_state: S, func: F) -&gt; <a class="struct" href="../../futures/future/struct.LoopFn.html" title="struct futures::future::LoopFn">LoopFn</a>&lt;A, F&gt; <span class="where fmt-newline">where<br>&nbsp;&nbsp;&nbsp;&nbsp;F: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnMut.html" title="trait core::ops::function::FnMut">FnMut</a>(S) -&gt; A,<br>&nbsp;&nbsp;&nbsp;&nbsp;A: <a class="trait" href="../../futures/future/trait.IntoFuture.html" title="trait futures::future::IntoFuture">IntoFuture</a>&lt;Item = <a class="enum" href="../../futures/future/enum.Loop.html" title="enum futures::future::Loop">Loop</a>&lt;T, S&gt;&gt;,&nbsp;</span></pre><div class='docblock'><p>Creates a new future implementing a tail-recursive loop.</p>
<p>The loop function is immediately called with <code>initial_state</code> and should
return a value that can be converted to a future. On successful completion,
this future should output a <code>Loop&lt;T, S&gt;</code> to indicate the status of the
loop.</p>
<p><code>Loop::Break(T)</code> halts the loop and completes the future with output <code>T</code>.</p>
<p><code>Loop::Continue(S)</code> reinvokes the loop function with state <code>S</code>. The returned
future will be subsequently polled for a new <code>Loop&lt;T, S&gt;</code> value.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">futures</span>::<span class="ident">future</span>::{<span class="ident">ok</span>, <span class="ident">loop_fn</span>, <span class="ident">Future</span>, <span class="ident">FutureResult</span>, <span class="ident">Loop</span>};
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">io</span>::<span class="ident">Error</span>;

<span class="kw">struct</span> <span class="ident">Client</span> {
    <span class="ident">ping_count</span>: <span class="ident">u8</span>,
}

<span class="kw">impl</span> <span class="ident">Client</span> {
    <span class="kw">fn</span> <span class="ident">new</span>() <span class="op">-&gt;</span> <span class="self">Self</span> {
        <span class="ident">Client</span> { <span class="ident">ping_count</span>: <span class="number">0</span> }
    }

    <span class="kw">fn</span> <span class="ident">send_ping</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">FutureResult</span><span class="op">&lt;</span><span class="self">Self</span>, <span class="ident">Error</span><span class="op">&gt;</span> {
        <span class="ident">ok</span>(<span class="ident">Client</span> { <span class="ident">ping_count</span>: <span class="self">self</span>.<span class="ident">ping_count</span> <span class="op">+</span> <span class="number">1</span> })
    }

    <span class="kw">fn</span> <span class="ident">receive_pong</span>(<span class="self">self</span>) <span class="op">-&gt;</span> <span class="ident">FutureResult</span><span class="op">&lt;</span>(<span class="self">Self</span>, <span class="ident">bool</span>), <span class="ident">Error</span><span class="op">&gt;</span> {
        <span class="kw">let</span> <span class="ident">done</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">ping_count</span> <span class="op">&gt;=</span> <span class="number">5</span>;
        <span class="ident">ok</span>((<span class="self">self</span>, <span class="ident">done</span>))
    }
}

<span class="kw">let</span> <span class="ident">ping_til_done</span> <span class="op">=</span> <span class="ident">loop_fn</span>(<span class="ident">Client</span>::<span class="ident">new</span>(), <span class="op">|</span><span class="ident">client</span><span class="op">|</span> {
    <span class="ident">client</span>.<span class="ident">send_ping</span>()
        .<span class="ident">and_then</span>(<span class="op">|</span><span class="ident">client</span><span class="op">|</span> <span class="ident">client</span>.<span class="ident">receive_pong</span>())
        .<span class="ident">and_then</span>(<span class="op">|</span>(<span class="ident">client</span>, <span class="ident">done</span>)<span class="op">|</span> {
            <span class="kw">if</span> <span class="ident">done</span> {
                <span class="prelude-val">Ok</span>(<span class="ident">Loop</span>::<span class="ident">Break</span>(<span class="ident">client</span>))
            } <span class="kw">else</span> {
                <span class="prelude-val">Ok</span>(<span class="ident">Loop</span>::<span class="ident">Continue</span>(<span class="ident">client</span>))
            }
        })
});</pre>
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