1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>has_trivial_assign</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.TypeTraits"> 8<link rel="up" href="../reference.html" title="Alphabetical Reference"> 9<link rel="prev" href="has_right_shift_assign.html" title="has_right_shift_assign"> 10<link rel="next" href="has_trivial_constructor.html" title="has_trivial_constructor"> 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="has_right_shift_assign.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="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="has_trivial_constructor.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_typetraits.reference.has_trivial_assign"></a><a class="link" href="has_trivial_assign.html" title="has_trivial_assign">has_trivial_assign</a> 28</h3></div></div></div> 29<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> 30<span class="keyword">struct</span> <span class="identifier">has_trivial_assign</span> <span class="special">:</span> <span class="keyword">public</span> <em class="replaceable"><code><a class="link" href="integral_constant.html" title="integral_constant">true_type</a>-or-<a class="link" href="integral_constant.html" title="integral_constant">false_type</a></code></em> <span class="special">{};</span> 31</pre> 32<p> 33 <span class="bold"><strong>Inherits:</strong></span> If T is a (possibly cv-qualified) 34 type with a trivial assignment-operator then inherits from <a class="link" href="integral_constant.html" title="integral_constant">true_type</a>, 35 otherwise inherits from <a class="link" href="integral_constant.html" title="integral_constant">false_type</a>. 36 </p> 37<p> 38 If a type has a trivial assignment-operator then the operator has the same 39 effect as copying the bits of one object to the other: calls to the operator 40 can be safely replaced with a call to <code class="computeroutput"><span class="identifier">memcpy</span></code>. 41 </p> 42<p> 43 <span class="bold"><strong>Compiler Compatibility:</strong></span> Without some (as 44 yet unspecified) help from the compiler, has_trivial_assign will never report 45 that a user-defined class or struct has a trivial constructor; this is always 46 safe, if possibly sub-optimal. In order to correctly handle deleted or private 47 assignment operators, the compiler must also support C++11's <code class="computeroutput"><span class="keyword">decltype</span></code>. Currently (May 2015) compilers more 48 recent than Visual C++ 8, GCC-4.3, Greenhills 6.0, Intel-11.0, and Codegear 49 have the necessary compiler <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> 50 to ensure that this trait "just works". You may also test to see 51 if the necessary <a class="link" href="../intrinsics.html" title="Support for Compiler Intrinsics">intrinsics</a> 52 are available by checking to see if the macro <code class="computeroutput"><span class="identifier">BOOST_HAS_TRIVIAL_ASSIGN</span></code> 53 is defined. 54 </p> 55<p> 56 <span class="bold"><strong>C++ Standard Reference:</strong></span> 12.8p11. 57 </p> 58<p> 59 <span class="bold"><strong>Header:</strong></span> <code class="computeroutput"> <span class="preprocessor">#include</span> 60 <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">/</span><span class="identifier">has_trivial_assign</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 61 or <code class="computeroutput"> <span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">type_traits</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code> 62 </p> 63<p> 64 <span class="bold"><strong>Examples:</strong></span> 65 </p> 66<div class="blockquote"><blockquote class="blockquote"><p> 67 <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> 68 inherits from <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. 69 </p></blockquote></div> 70<div class="blockquote"><blockquote class="blockquote"><p> 71 <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special"><</span><span class="keyword">char</span><span class="special">*>::</span><span class="identifier">type</span></code> is the type <code class="computeroutput"><a class="link" href="integral_constant.html" title="integral_constant">true_type</a></code>. 72 </p></blockquote></div> 73<div class="blockquote"><blockquote class="blockquote"><p> 74 <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special"><</span><span class="keyword">int</span> <span class="special">(*)(</span><span class="keyword">long</span><span class="special">)>::</span><span class="identifier">value</span></code> is an integral constant expression 75 that evaluates to <span class="emphasis"><em>true</em></span>. 76 </p></blockquote></div> 77<div class="blockquote"><blockquote class="blockquote"><p> 78 <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special"><</span><span class="identifier">MyClass</span><span class="special">>::</span><span class="identifier">value</span></code> is an integral constant expression 79 that evaluates to <span class="emphasis"><em>false</em></span>. 80 </p></blockquote></div> 81<div class="blockquote"><blockquote class="blockquote"><p> 82 <code class="computeroutput"><span class="identifier">has_trivial_assign</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_type</span></code> is the type <code class="computeroutput"><span class="keyword">bool</span></code>. 83 </p></blockquote></div> 84</div> 85<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 86<td align="left"></td> 87<td align="right"><div class="copyright-footer">Copyright © 2000, 2011 Adobe Systems Inc, David Abrahams, 88 Frederic Bron, Steve Cleary, Beman Dawes, Glen Fernandes, Aleksey Gurtovoy, 89 Howard Hinnant, Jesse Jones, Mat Marcus, Itay Maman, John Maddock, Alexander 90 Nasonov, Thorsten Ottosen, Roman Perepelitsa, Robert Ramey, Jeremy Siek, Robert 91 Stewart and Steven Watanabe<p> 92 Distributed under the Boost Software License, Version 1.0. (See accompanying 93 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>) 94 </p> 95</div></td> 96</tr></table> 97<hr> 98<div class="spirit-nav"> 99<a accesskey="p" href="has_right_shift_assign.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="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="has_trivial_constructor.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a> 100</div> 101</body> 102</html> 103
