1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Reference</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="Boost.Optional"> 8<link rel="up" href="../index.html" title="Boost.Optional"> 9<link rel="prev" href="../boost_optional/tutorial/performance_considerations.html" title="Performance considerations"> 10<link rel="next" href="../boost_optional/reference/header__boost_optional_bad_optional_access_hpp_.html" title="Header <boost/optional/bad_optional_access.hpp>"> 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="../boost_optional/tutorial/performance_considerations.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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_optional/reference/header__boost_optional_bad_optional_access_hpp_.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 27<a name="optional.reference"></a><a class="link" href="reference.html" title="Reference">Reference</a> 28</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="reference.html#boost_optional.reference.header__boost_none_hpp_">Header 31 <boost/none.hpp></a></span></dt> 32<dt><span class="section"><a href="../boost_optional/reference/header__boost_optional_bad_optional_access_hpp_.html">Header 33 <boost/optional/bad_optional_access.hpp></a></span></dt> 34<dt><span class="section"><a href="../boost_optional/reference/io_header.html">Header <boost/optional/optional_io.hpp></a></span></dt> 35<dt><span class="section"><a href="../boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html">Header 36 <boost/optional/optional_fwd.hpp></a></span></dt> 37<dt><span class="section"><a href="reference/header__boost_optional_optional_hpp_.html">Header 38 <boost/optional/optional.hpp></a></span></dt> 39<dt><span class="section"><a href="../boost_optional/reference/header__boost_optional_hpp_.html">Header 40 <boost/optional.hpp></a></span></dt> 41</dl></div> 42<div class="section"> 43<div class="titlepage"><div><div><h3 class="title"> 44<a name="boost_optional.reference.header__boost_none_hpp_"></a><a class="link" href="reference.html#boost_optional.reference.header__boost_none_hpp_" title="Header <boost/none.hpp>">Header 45 <boost/none.hpp></a> 46</h3></div></div></div> 47<div class="section"> 48<div class="titlepage"><div><div><h4 class="title"> 49<a name="boost_optional.reference.header__boost_none_hpp_.synopsis"></a><a class="link" href="reference.html#boost_optional.reference.header__boost_none_hpp_.synopsis" title="Synopsis">Synopsis</a> 50</h4></div></div></div> 51<p> 52</p> 53<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 54 55<span class="keyword">class</span> <span class="identifier">none_t</span> <span class="special">{/*</span> <span class="identifier">see</span> <span class="identifier">below</span> <span class="special">*/};</span> 56 57<span class="keyword">const</span> <span class="identifier">none_t</span> <span class="identifier">none</span> <span class="special">(/*</span> <span class="identifier">see</span> <span class="identifier">below</span> <span class="special">*/);</span> 58 59<span class="special">}</span> <span class="comment">// namespace boost</span> 60</pre> 61<p> 62 </p> 63<p> 64 Class <code class="computeroutput"><span class="identifier">none_t</span></code> is meant to 65 serve as a tag for selecting appropriate overloads of from <code class="computeroutput"><span class="identifier">optional</span></code>'s interface. It is an empty, 66 trivially copyable class with disabled default constructor. 67 </p> 68<p> 69 Constant <code class="computeroutput"><span class="identifier">none</span></code> is used to 70 indicate an optional object that does not contain a value in initialization, 71 assignment and relational operations of <code class="computeroutput"><span class="identifier">optional</span></code>. 72 </p> 73</div> 74</div> 75</div> 76<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 77<td align="left"></td> 78<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p> 79 Distributed under the Boost Software License, Version 1.0. (See accompanying 80 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>) 81 </p> 82</div></td> 83</tr></table> 84<hr> 85<div class="spirit-nav"> 86<a accesskey="p" href="../boost_optional/tutorial/performance_considerations.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.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_optional/reference/header__boost_optional_bad_optional_access_hpp_.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 87</div> 88</body> 89</html> 90
