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<span class="m-breadcrumb"><a href="tutorial.html">Tutorial</a> »</span>
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Promisify functions
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</h1>
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<p>Explains how to promisify callback taking functions into a <a href="classcti_1_1continuable__base.html" class="m-dox">continuable_<wbr />base</a>.</p>
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<h3>Contents</h3>
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<ul>
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<li><a href="#tutorial-promisify-continuables-promisify">Promisification and continuables</a></li>
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<li><a href="#tutorial-promisify-continuables-boost">Promisify boost::asio</a></li>
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<section id="tutorial-promisify-continuables-promisify"><h2><a href="#tutorial-promisify-continuables-promisify">Promisification and continuables</a></h2><p>The promisification has a longer history in the JavaScript world where the legacy way of asynchronous programming was the usage of callbacks of the form <code class="m-code"><span class="kd">function</span><span class="p">(</span><span class="nx">error</span><span class="p">,</span> <span class="nx">result</span><span class="p">...)</span></code>. The ideal way of dealing with such an asynchronous result is to return a promise and soon utility helpers were provided to do so.</p><p>The usage of callbacks to represent an asynchronous result is still a popular way nowadays. Thus the library provides the <a href="classcti_1_1promisify.html" class="m-dox">promisify</a> helper class which makes it possible to convert callback taking functions of various styles into one that returns a <a href="classcti_1_1continuable__base.html" class="m-dox">continuable_<wbr />base</a> instead.</p><aside class="m-note m-info"><h4>Note</h4><p>Providing promisified APIs for other popular libraries is out of scope for this library. However contributions are highly welcome to add more conversion helpers for other commonly used callback styles.</p></aside></section><section id="tutorial-promisify-continuables-boost"><h2><a href="#tutorial-promisify-continuables-boost">Promisify boost::asio</a></h2><p>The default callback style is something like <code class="m-code"><span class="kd">function</span><span class="p">(</span><span class="nx">error</span><span class="p">,</span> <span class="nx">result</span><span class="p">...)</span></code> as described above. Continuable offers the <a href="classcti_1_1promisify.html#a28834d45efa0e6d2e22771cdd38e33a4" class="m-dox">promisify::<wbr />from</a> method for such callback styles.</p><p>See an example of how to promisify boost asio's <code>async_resolve</code> below:</p><pre class="m-code"><span class="k">auto</span> <span class="nf">async_resolve</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">host</span><span class="p">,</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span> <span class="n">service</span><span class="p">)</span> <span class="p">{</span>
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<span class="k">return</span> <span class="n">cti</span><span class="o">::</span><span class="n">promisify</span><span class="o"><</span><span class="n">asio</span><span class="o">::</span><span class="n">ip</span><span class="o">::</span><span class="n">udp</span><span class="o">::</span><span class="n">resolver</span><span class="o">::</span><span class="n">iterator</span><span class="o">>::</span><span class="n">from</span><span class="p">(</span>
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<span class="p">[</span><span class="o">&</span><span class="p">](</span><span class="k">auto</span><span class="o">&&</span><span class="p">...</span> <span class="n">args</span><span class="p">)</span> <span class="p">{</span>
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<span class="n">resolver_</span><span class="p">.</span><span class="n">async_resolve</span><span class="p">(</span><span class="n">std</span><span class="o">::</span><span class="n">forward</span><span class="o"><</span><span class="k">decltype</span><span class="p">(</span><span class="n">args</span><span class="p">)</span><span class="o">></span><span class="p">(</span><span class="n">args</span><span class="p">)...);</span>
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<span class="p">},</span>
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<span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">host</span><span class="p">),</span> <span class="n">std</span><span class="o">::</span><span class="n">move</span><span class="p">(</span><span class="n">service</span><span class="p">));</span>
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<span class="p">}</span></pre><p>Then it should be possible to use <code>asio::async_resolve</code> like this:</p><pre class="m-code"><span class="n">async_resolve</span><span class="p">(</span><span class="s">"127.0.0.1"</span><span class="p">,</span> <span class="s">"daytime"</span><span class="p">)</span>
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<span class="p">.</span><span class="n">then</span><span class="p">([](</span><span class="n">udp</span><span class="o">::</span><span class="n">resolver</span><span class="o">::</span><span class="n">iterator</span> <span class="n">iterator</span><span class="p">)</span> <span class="p">{</span>
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<span class="c1">// ...</span>
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<span class="p">});</span></pre></section>
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<b><a href="https://github.com/Naios/continuable">continuable</a></b> - C++14 allocation aware futures</br>Copyright 2015–2018 <a href="https://github.com/Naios">Denis Blank</a>. Contact the author via <a href="mailto:denis.blank@outlook.com">e-mail</a>.</br>Powered by <a href="http://doxygen.org/">Doxygen</a> and <a href="http://mcss.mosra.cz/">m.css</a>
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