1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Receiver concepts</title> 5<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../boost_asio.html" title="Boost.Asio"> 8<link rel="up" href="../reference.html" title="Reference"> 9<link rel="prev" href="ReadHandler.html" title="Read handler requirements"> 10<link rel="next" href="ResolveHandler.html" title="Resolve handler requirements"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> 15<td align="center"><a href="../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="ReadHandler.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="ResolveHandler.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_asio.reference.Receiver"></a><a class="link" href="Receiver.html" title="Receiver concepts">Receiver concepts</a> 28</h3></div></div></div> 29<p> 30 A receiver represents the continuation of an asynchronous operation. An asynchronous 31 operation may complete with a (possibly empty) set of values, an error, or 32 it may be cancelled. A receiver has three principal operations corresponding 33 to the three ways an asynchronous operation may complete: <code class="computeroutput">set_value</code>, 34 <code class="computeroutput">set_error</code>, and <code class="computeroutput">set_done</code>. These are collectively 35 known as a receiver’s <span class="emphasis"><em>completion-signal operations</em></span>. 36 </p> 37<pre class="programlisting">template<class T, class E = exception_ptr> 38concept receiver = 39 move_constructible<remove_cvref_t<T>> && 40 constructible_from<remove_cvref_t<T>, T> && 41 requires(remove_cvref_t<T>&& t, E&& e) { 42 { execution::set_done(std::move(t)) } noexcept; 43 { execution::set_error(std::move(t), (E&&) e) } noexcept; 44 }; 45 46template<class T, class... An> 47concept receiver_of = 48 receiver<T> && 49 requires(remove_cvref_t<T>&& t, An&&... an) { 50 execution::set_value(std::move(t), (An&&) an...); 51 }; 52</pre> 53<p> 54 The receiver’s completion-signal operations have semantic requirements 55 that are collectively known as the <span class="emphasis"><em>receiver contract</em></span>, 56 described below: 57 </p> 58<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 59<li class="listitem"> 60 None of a receiver’s completion-signal operations shall be invoked 61 before <code class="computeroutput">execution::start</code> has been called on the operation 62 state object that was returned by <code class="computeroutput">execution::connect</code> to 63 connect that receiver to a sender. 64 </li> 65<li class="listitem"> 66 Once <code class="computeroutput">execution::start</code> has been called on the operation state 67 object, exactly one of the receiver’s completion-signal operations 68 shall complete non-exceptionally before the receiver is destroyed. 69 </li> 70<li class="listitem"> 71 If <code class="computeroutput">execution::set_value</code> exits with an exception, it is still 72 valid to call <code class="computeroutput">execution::set_error</code> or <code class="computeroutput">execution::set_done</code> 73 on the receiver. 74 </li> 75</ul></div> 76<p> 77 Once one of a receiver’s completion-signal operations has completed non-exceptionally, 78 the receiver contract has been satisfied. 79 </p> 80</div> 81<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 82<td align="left"></td> 83<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 84 Kohlhoff<p> 85 Distributed under the Boost Software License, Version 1.0. (See accompanying 86 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>) 87 </p> 88</div></td> 89</tr></table> 90<hr> 91<div class="spirit-nav"> 92<a accesskey="p" href="ReadHandler.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="ResolveHandler.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 93</div> 94</body> 95</html> 96
