query.html
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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.query"></a><a class="link" href="query.html" title="query">query</a>
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<p>
<a class="indexterm" name="asio.indexterm.query"></a>
A customisation point that queries the value of
a property.
</p>
<pre class="programlisting">constexpr unspecified query = unspecified;
</pre>
<p>
The name <code class="computeroutput">query</code> denotes a customization point object. The expression
<code class="computeroutput">asio::query(E, P)</code> for some subexpressions <code class="computeroutput">E</code> and
<code class="computeroutput">P</code> (with types <code class="computeroutput">T = decay_t<decltype(E)></code> and
<code class="computeroutput">Prop = decay_t<decltype(P)></code>) is expression-equivalent
to:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
If <code class="computeroutput">is_applicable_property_v<T, Prop></code> is not a well-formed
constant expression with value <code class="computeroutput">true</code>, <code class="computeroutput">asio::query(E,
P)</code> is ill-formed.
</li>
<li class="listitem">
Otherwise, <code class="computeroutput">Prop::template static_query_v<T></code> if the
expression <code class="computeroutput">Prop::template static_query_v<T></code> is a well-formed
constant expression.
</li>
<li class="listitem">
Otherwise, <code class="computeroutput">(E).query(P)</code> if the expression <code class="computeroutput">(E).query(P)</code>
is well-formed.
</li>
<li class="listitem">
Otherwise, <code class="computeroutput">query(E, P)</code> if the expression <code class="computeroutput">query(E,
P)</code> is a valid expression with overload resolution performed in
a context that does not include the declaration of the <code class="computeroutput">query</code>
customization point object.
</li>
<li class="listitem">
Otherwise, <code class="computeroutput">asio::query(E, P)</code> is ill-formed.
</li>
</ul></div>
<h5>
<a name="asio.reference.query.h0"></a>
<span><a name="asio.reference.query.requirements"></a></span><a class="link" href="query.html#asio.reference.query.requirements">Requirements</a>
</h5>
<p>
<span class="emphasis"><em>Header: </em></span><code class="literal">asio/query.hpp</code>
</p>
<p>
<span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M.
Kohlhoff<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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