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<div class="titlepage"><div><div><h1 style="clear: both">Coroutines</h1></div></div></div>
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<p><a href="../../changelog.html">In v2.1.2</a> Outcome published official support for using
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Outcome within C++ coroutines. This page documents that support.</p>
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<p>All standard C++ Coroutines have the following form:</p>
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<div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="c1">// Coroutine functions MUST return an AWAITABLE type
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</span><span class="c1"></span><span class="n">AWAITABLE</span><span class="o"><</span><span class="kt">int</span><span class="o">></span> <span class="n">function_name</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="p">...</span> <span class="n">ordinary</span> <span class="n">C</span><span class="o">++</span> <span class="p">...</span>
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<span class="k">if</span><span class="p">(</span><span class="o">!</span><span class="p">...)</span>
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<span class="p">{</span>
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<span class="n">co_return</span> <span class="mi">5</span><span class="p">;</span> <span class="c1">// CANNOT use ordinary 'return' from coroutines
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</span><span class="c1"></span> <span class="p">}</span>
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<span class="p">...</span>
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<span class="c1">// Possibly suspend this coroutine's execution until the
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</span><span class="c1"></span> <span class="c1">// awaitable resumes execution of dependent code
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</span><span class="c1"></span> <span class="k">auto</span> <span class="n">x</span> <span class="o">=</span> <span class="n">co_await</span> <span class="n">expr_resulting_in_AWAITABLE</span><span class="p">;</span>
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<span class="p">...</span>
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<span class="p">}</span>
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</code></pre></div>
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<p>The type <code>AWAITABLE<T></code> is any type which publishes the Coroutine protocol telling
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C++ how to suspend and resume execution of a coroutine which returns a <code>T</code>. It is out of scope of
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this page to document how to do this, however note that the <code>eager<T, Executor = void></code> and <code>lazy<T, Executor = void></code>
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types below are completely generic awaitables suitable for use in ANY code.
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They <strong>only</strong> behave differently if <code>T</code>, the type being returned by the awaitable,
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is an Outcome type e.g. <code>outcome::basic_result</code> or <code>outcome::basic_outcome</code>.</p>
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</div><p><small>Last revised: March 18, 2022 at 14:45:32 UTC</small></p>
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