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<title>ValueOrNone&lt;T&gt; - Boost.Outcome documentation</title>
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  <div class="titlepage"><div><div><h1 style="clear: both"><code>ValueOrNone&lt;T&gt;</code></h1></div></div></div>
  <p>If on C++ 20 or the Concepts TS is enabled, a boolean concept matching types with a public <code>.has_value()</code> observer which returns <code>bool</code>, and a public <code>.value()</code> observer function.</p>

<p>If without Concepts, a static constexpr bool which is true for types matching the same requirements, using a SFINAE based emulation.</p>

<p>This concept matches optional-like types such as 
<a href="https://en.cppreference.com/w/cpp/utility/optional" class="api-reference" target="_blank"><i class="fa fa-book" aria-hidden="true"></i> <code>std::optional&lt;T&gt;</code></a>
. Note it also matches 
<a href="https://wg21.link/P0323" class="api-reference" target="_blank"><i class="fa fa-book" aria-hidden="true"></i> P0323 <code>std::expected&lt;T, E&gt;</code></a>
, which also has an optional-like interface. You may thus wish to preferentially match <a href="../../reference/concepts/valueorerror.html" class="api-reference"><code>ValueOrError&lt;T, E&gt;</code></a>
 for any given <code>T</code>.</p>

<p><em>Namespace</em>: <code>BOOST_OUTCOME_V2_NAMESPACE::convert</code></p>

<p><em>Header</em>: <code>&lt;boost/outcome/convert.hpp&gt;</code></p>


        </div><p><small>Last revised: December 13, 2018 at 17:36:11 UTC</small></p>
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