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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.require_concept"></a><a class="link" href="require_concept.html" title="require_concept">require_concept</a>
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<p>
        <a class="indexterm" name="boost_asio.indexterm.require_concept"></a> 
A customisation point
        that applies a concept-enforcing property to an object.
      </p>
<pre class="programlisting">constexpr unspecified require_concept = unspecified;
</pre>
<p>
        The name <code class="computeroutput">require_concept</code> denotes a customization point object.
        The expression <code class="computeroutput">boost::asio::require_concept(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&lt;decltype(E)&gt;</code>
        and <code class="computeroutput">Prop = decay_t&lt;decltype(P)&gt;</code>) is expression-equivalent
        to:
      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
            If <code class="computeroutput">is_applicable_property_v&lt;T, Prop&gt; &amp;&amp; Prop::is_requirable_concept</code>
            is not a well-formed constant expression with value <code class="computeroutput">true</code>,
            <code class="computeroutput">boost::asio::require_concept(E, P)</code> is ill-formed.
          </li>
<li class="listitem">
            Otherwise, <code class="computeroutput">E</code> if the expression <code class="computeroutput">Prop::template static_query_v&lt;T&gt;
            == Prop::value()</code> is a well-formed constant expression with value
            <code class="computeroutput">true</code>.
          </li>
<li class="listitem">
            Otherwise, <code class="computeroutput">(E).require_concept(P)</code> if the expression <code class="computeroutput">(E).require_concept(P)</code>
            is well-formed.
          </li>
<li class="listitem">
            Otherwise, <code class="computeroutput">require_concept(E, P)</code> if the expression <code class="computeroutput">require_concept(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">require_concept</code>
            customization point object.
          </li>
<li class="listitem">
            Otherwise, <code class="computeroutput">boost::asio::require_concept(E, P)</code> is ill-formed.
          </li>
</ul></div>
<h5>
<a name="boost_asio.reference.require_concept.h0"></a>
        <span class="phrase"><a name="boost_asio.reference.require_concept.requirements"></a></span><a class="link" href="require_concept.html#boost_asio.reference.require_concept.requirements">Requirements</a>
      </h5>
<p>
        <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/require_concept.hpp</code>
      </p>
<p>
        <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
      </p>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2021 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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