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- <div class="titlepage"><div><div><h3 class="title">
- <a name="boost_typetraits.reference.is_detected"></a><a class="link" href="is_detected.html" title="is_detected">is_detected</a>
- </h3></div></div></div>
- <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...></span> <span class="keyword">class</span> <span class="identifier">Op</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
- <span class="keyword">using</span> <span class="identifier">is_detected</span> <span class="special">=</span> <em class="replaceable"><code>see-below</code></em><span class="special">;</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...></span> <span class="keyword">class</span> <span class="identifier">Op</span><span class="special">,</span> <span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
- <span class="keyword">constexpr</span> <span class="keyword">bool</span> <span class="identifier">is_detected_v</span> <span class="special">=</span> <span class="identifier">is_detected</span><span class="special"><</span><span class="identifier">Op</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">...>::</span><span class="identifier">value</span><span class="special">;</span>
- </pre>
- <p>
- <span class="bold"><strong>Aliases:</strong></span> If <code class="computeroutput"><span class="identifier">Op</span><span class="special"><</span><span class="identifier">Args</span><span class="special">...></span></code> is a valid template-id, aliases <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>,
- otherwise aliases <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>.
- </p>
- <p>
- <span class="bold"><strong>C++ Standard Paper:</strong></span> <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4502.pdf" target="_top">N4502</a>
- </p>
- <p>
- <span class="bold"><strong>Compiler Compatibility:</strong></span> Requires C++11 variadic
- templates and C++11 template aliases.
- </p>
- <p>
- <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"><span class="preprocessor">#include</span>
- <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">is_detected</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>
- </p>
- <p>
- <span class="bold"><strong>Examples:</strong></span>
- </p>
- <p>
- Suppose we wish to "reset" a value of type T, if the type has a
- <code class="computeroutput"><span class="identifier">clear</span><span class="special">()</span></code>
- member function then we should call it, otherwise we should assign a default
- constructed value:
- </p>
- <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
- <span class="keyword">using</span> <span class="identifier">clear_t</span> <span class="special">=</span> <span class="keyword">decltype</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">declval</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>().</span><span class="identifier">clear</span><span class="special">());</span>
- <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
- <span class="keyword">void</span> <span class="identifier">clear</span><span class="special">(</span><span class="identifier">T</span><span class="special">&</span> <span class="identifier">value</span><span class="special">)</span>
- <span class="special">{</span>
- <span class="keyword">if</span> <span class="keyword">constexpr</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">is_detected_v</span><span class="special"><</span><span class="identifier">clear_t</span><span class="special">,</span> <span class="identifier">T</span><span class="special">>)</span> <span class="special">{</span>
- <span class="identifier">value</span><span class="special">.</span><span class="identifier">clear</span><span class="special">();</span>
- <span class="special">}</span> <span class="keyword">else</span> <span class="special">{</span>
- <span class="identifier">value</span> <span class="special">=</span> <span class="identifier">T</span><span class="special">();</span>
- <span class="special">}</span>
- <span class="special">}</span>
- </pre>
- <p>
- See also: <a class="link" href="is_detected_convertible.html" title="is_detected_convertible">is_detected_convertible</a>,
- <a class="link" href="is_detected_exact.html" title="is_detected_exact">is_detected_exact</a>.
- </p>
- </div>
- <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
- <td align="left"></td>
- <td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams,
- Frederic Bron, Steve Cleary, Beman Dawes, Aleksey Gurtovoy, Howard Hinnant,
- Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander Nasonov, Thorsten
- Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert Stewart and Steven
- Watanabe<p>
- Distributed under the Boost Software License, Version 1.0. (See accompanying
- file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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