1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>has_get_executor</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="../../index.html" title="Chapter 1. Boost.Beast"> 8<link rel="up" href="../ref.html" title="This Page Intentionally Left Blank 2/2"> 9<link rel="prev" href="boost__beast__executor_type.html" title="executor_type"> 10<link rel="next" href="boost__beast__is_sync_read_stream.html" title="is_sync_read_stream"> 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" 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35<h5> 36<a name="beast.ref.boost__beast__has_get_executor.h0"></a> 37 <span class="phrase"><a name="beast.ref.boost__beast__has_get_executor.synopsis"></a></span><a class="link" href="boost__beast__has_get_executor.html#beast.ref.boost__beast__has_get_executor.synopsis">Synopsis</a> 38 </h5> 39<p> 40 Defined in header <code class="literal"><<a href="../../../../../../boost/beast/core/stream_traits.hpp" target="_top">boost/beast/core/stream_traits.hpp</a>></code> 41 </p> 42<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> 43 <span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 44<span class="keyword">using</span> <span class="identifier">has_get_executor</span> <span class="special">=</span> <span class="emphasis"><em>see-below</em></span><span class="special">;</span> 45</pre> 46<h5> 47<a name="beast.ref.boost__beast__has_get_executor.h1"></a> 48 <span class="phrase"><a name="beast.ref.boost__beast__has_get_executor.description"></a></span><a class="link" href="boost__beast__has_get_executor.html#beast.ref.boost__beast__has_get_executor.description">Description</a> 49 </h5> 50<p> 51 Metafunctions are used to perform compile time checking of template types. 52 This type will be <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">true_type</span></code> if <code class="computeroutput"><span class="identifier">T</span></code> 53 has the member function with the correct signature, else type will be <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">false_type</span></code>. 54 </p> 55<h5> 56<a name="beast.ref.boost__beast__has_get_executor.h2"></a> 57 <span class="phrase"><a name="beast.ref.boost__beast__has_get_executor.example"></a></span><a class="link" href="boost__beast__has_get_executor.html#beast.ref.boost__beast__has_get_executor.example">Example</a> 58 </h5> 59<p> 60 Use with tag dispatching: 61 </p> 62<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 63<span class="keyword">void</span> <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">t</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">true_type</span><span class="special">)</span> 64<span class="special">{</span> 65 <span class="identifier">net</span><span class="special">::</span><span class="identifier">post</span><span class="special">(</span> 66 <span class="identifier">t</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">(),</span> 67 <span class="special">[]</span> 68 <span class="special">{</span> 69 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Hello, world!"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span> 70 <span class="special">});</span> 71<span class="special">}</span> 72 73<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 74<span class="keyword">void</span> <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">false_type</span><span class="special">)</span> 75<span class="special">{</span> 76 <span class="comment">// T does not have get_executor</span> 77<span class="special">}</span> 78 79<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 80<span class="keyword">void</span> <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">t</span><span class="special">)</span> 81<span class="special">{</span> 82 <span class="identifier">maybe_hello</span><span class="special">(</span><span class="identifier">t</span><span class="special">,</span> <span class="identifier">has_get_executor</span><span class="special"><</span><span class="identifier">T</span><span class="special">>{});</span> 83<span class="special">}</span> 84</pre> 85<p> 86 Use with <code class="computeroutput"><span class="keyword">static_assert</span></code>: 87 </p> 88<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">stream</span> 89<span class="special">{</span> 90 <span class="keyword">using</span> <span class="identifier">executor_type</span> <span class="special">=</span> <span class="identifier">net</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">executor_type</span><span class="special">;</span> 91 <span class="identifier">executor_type</span> <span class="identifier">get_executor</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span> 92<span class="special">};</span> 93 94<span class="keyword">static_assert</span><span class="special">(</span><span class="identifier">has_get_executor</span><span class="special"><</span><span class="identifier">stream</span><span class="special">>::</span><span class="identifier">value</span><span class="special">,</span> <span class="string">"Missing get_executor member"</span><span class="special">);</span> 95</pre> 96</div> 97<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 98<td align="left"></td> 99<td align="right"><div class="copyright-footer">Copyright © 2016-2019 Vinnie 100 Falco<p> 101 Distributed under the Boost Software License, Version 1.0. (See accompanying 102 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>) 103 </p> 104</div></td> 105</tr></table> 106<hr> 107<div class="spirit-nav"> 108<a accesskey="p" href="boost__beast__executor_type.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../ref.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="boost__beast__is_sync_read_stream.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 109</div> 110</body> 111</html> 112
