<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>require_concept</title> <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> <link rel="home" href="../../boost_asio.html" title="Boost.Asio"> <link rel="up" href="../reference.html" title="Reference"> <link rel="prev" href="require.html" title="require"> <link rel="next" href="require_concept_result.html" title="require_concept_result"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> <td align="center"><a href="../../../../index.html">Home</a></td> <td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> <td align="center"><a href="../../../../more/index.htm">More</a></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="require.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="require_concept_result.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> </div> <div class="section"> <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> </h3></div></div></div> <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<decltype(E)></code> and <code class="computeroutput">Prop = decay_t<decltype(P)></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<T, Prop> && 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<T> == 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> </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 © 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>) </p> </div></td> </tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="require.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="require_concept_result.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>