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<title>TRY avoiding copy/move - Boost.Outcome documentation</title>
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<div class="titlepage"><div><div><h1 style="clear: both">TRY avoiding copy/move</h1></div></div></div>
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<p><a href="../../../reference/macros/tryv.html" class="api-reference"><code>BOOST_OUTCOME_TRYV(expr)/BOOST_OUTCOME_TRY(expr)</code></a>
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works by creating an internal uniquely
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named variable which holds the value emitted by the expression. This implies that a copy
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or move operation shall be performed on the object emitted (unless you are on C++ 17 or
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later, which has guaranteed copy elision), which may be undesirable for your use case.</p>
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<p>You can tell <code>BOOST_OUTCOME_TRY</code> to use a reference rather than a value for the internal
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uniquely named variable like this:</p>
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<div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="c1">// This refers to a Result containing an immovable object
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</span><span class="c1"></span><span class="n">outcome</span><span class="o">::</span><span class="n">result</span><span class="o"><</span><span class="n">Immovable</span><span class="o">></span> <span class="o">&&</span><span class="n">res</span><span class="p">;</span>
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<span class="c1">// For when you do want to extract the value
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</span><span class="c1">// This creates an auto &&unique = res, followed by an
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</span><span class="c1">// auto &&v = std::move(unique).assume_value()
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</span><span class="c1"></span><span class="n">BOOST_OUTCOME_TRY</span><span class="p">((</span><span class="k">auto</span> <span class="o">&&</span><span class="p">,</span> <span class="n">v</span><span class="p">),</span> <span class="n">res</span><span class="p">);</span>
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</code></pre></div>
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<p>If you don’t care about extracting the value:</p>
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<div class="highlight"><pre class="chroma"><code class="language-c++" data-lang="c++"><span class="c1">// For when you don't want to extract the value
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</span><span class="c1">// This creates an auto &&unique = res
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</span><span class="c1"></span><span class="n">BOOST_OUTCOME_TRYV2</span><span class="p">(</span><span class="k">auto</span> <span class="o">&&</span><span class="p">,</span> <span class="n">res</span><span class="p">);</span>
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</code></pre></div>
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</div><p><small>Last revised: February 12, 2021 at 20:25:43 UTC</small></p>
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