94 lines
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94 lines
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="boost_asio.reference.query"></a><a class="link" href="query.html" title="query">query</a>
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</h3></div></div></div>
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<p>
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<a class="indexterm" name="boost_asio.indexterm.query"></a>
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A customisation point that queries the value
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of a property.
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</p>
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<pre class="programlisting">constexpr unspecified query = unspecified;
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</pre>
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<p>
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The name <code class="computeroutput">query</code> denotes a customization point object. The expression
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<code class="computeroutput">boost::asio::query(E, P)</code> for some subexpressions <code class="computeroutput">E</code>
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and <code class="computeroutput">P</code> (with types <code class="computeroutput">T = decay_t<decltype(E)></code>
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and <code class="computeroutput">Prop = decay_t<decltype(P)></code>) is expression-equivalent
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to:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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If <code class="computeroutput">is_applicable_property_v<T, Prop></code> is not a well-formed
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constant expression with value <code class="computeroutput">true</code>, <code class="computeroutput">boost::asio::query(E,
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P)</code> is ill-formed.
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</li>
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<li class="listitem">
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Otherwise, <code class="computeroutput">Prop::template static_query_v<T></code> if the
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expression <code class="computeroutput">Prop::template static_query_v<T></code> is a well-formed
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constant expression.
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</li>
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<li class="listitem">
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Otherwise, <code class="computeroutput">(E).query(P)</code> if the expression <code class="computeroutput">(E).query(P)</code>
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is well-formed.
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</li>
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<li class="listitem">
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Otherwise, <code class="computeroutput">query(E, P)</code> if the expression <code class="computeroutput">query(E,
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P)</code> is a valid expression with overload resolution performed in
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a context that does not include the declaration of the <code class="computeroutput">query</code>
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customization point object.
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</li>
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<li class="listitem">
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Otherwise, <code class="computeroutput">boost::asio::query(E, P)</code> is ill-formed.
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</li>
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</ul></div>
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<h5>
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<a name="boost_asio.reference.query.h0"></a>
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<span class="phrase"><a name="boost_asio.reference.query.requirements"></a></span><a class="link" href="query.html#boost_asio.reference.query.requirements">Requirements</a>
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</h5>
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<p>
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<span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/query.hpp</code>
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</p>
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<p>
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<span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
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</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 Christopher
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M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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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