1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Reference</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../any.html" title="Chapter 4. Boost.Any"> 10<link rel="prev" href="s02.html" title="Examples"> 11<link rel="next" href="../boost/bad_any_cast.html" title="Class bad_any_cast"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="s02.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../any.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/bad_any_cast.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="any.reference"></a>Reference</h2></div></div></div> 29<div class="toc"><dl class="toc"> 30<dt><span class="section"><a href="reference.html#any.ValueType"><span class="emphasis"><em>ValueType</em></span> requirements</a></span></dt> 31<dt><span class="section"><a href="reference.html#header.boost.any_hpp">Header <boost/any.hpp></a></span></dt> 32</dl></div> 33<div class="section"> 34<div class="titlepage"><div><div><h3 class="title"> 35<a name="any.ValueType"></a><span class="emphasis"><em>ValueType</em></span> requirements</h3></div></div></div> 36<p>Values are strongly informational objects for which 37 identity is not significant, i.e. the focus is principally on 38 their state content and any behavior organized around 39 that. Another distinguishing feature of values is their 40 granularity: normally fine-grained objects representing simple 41 concepts in the system such as quantities.</p> 42<p>As the emphasis of a value lies in its state not its 43 identity, values can be copied and typically assigned one to 44 another, requiring the explicit or implicit definition of a 45 public copy constructor and public assignment operator. Values 46 typically live within other scopes, i.e. within objects or 47 blocks, rather than on the heap. Values are therefore normally 48 passed around and manipulated directly as variables or through 49 references, but not as pointers that emphasize identity and 50 indirection.</p> 51<p>The specific requirements on value types to be used in an 52 <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">any</a></code> 53 are:</p> 54<div class="itemizedlist"><ul class="itemizedlist compact" style="list-style-type: disc; "> 55<li class="listitem">A <span class="emphasis"><em>ValueType</em></span> is 56 <span class="emphasis"><em>CopyConstructible</em></span> [20.1.3].</li> 57<li class="listitem">The destructor for a 58 <span class="emphasis"><em>ValueType</em></span> upholds the no-throw 59 exception-safety guarantee.</li> 60</ul></div> 61</div> 62<div class="section"> 63<div class="titlepage"><div><div><h3 class="title"> 64<a name="header.boost.any_hpp"></a>Header <<a href="../../../boost/any.hpp" target="_top">boost/any.hpp</a>></h3></div></div></div> 65<pre class="synopsis"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> 66 <span class="keyword">class</span> <a class="link" href="../boost/bad_any_cast.html" title="Class bad_any_cast">bad_any_cast</a><span class="special">;</span> 67 <span class="keyword">class</span> <a class="link" href="../boost/any.html" title="Class any">any</a><span class="special">;</span> 68 <span class="keyword">void</span> <a class="link" href="../boost/swap_1_3_5_5_2_1_3.html" title="Function swap"><span class="identifier">swap</span></a><span class="special">(</span><a class="link" href="../boost/any.html" title="Class any">any</a> <span class="special">&</span><span class="special">,</span> <a class="link" href="../boost/any.html" title="Class any">any</a> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 69 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="identifier">T</span> <a class="link" href="../boost/any_cast.html" title="Function any_cast"><span class="identifier">any_cast</span></a><span class="special">(</span><a class="link" href="../boost/any.html" title="Class any">any</a> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 70 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="identifier">T</span> <a class="link" href="../boost/any_cast.html" title="Function any_cast"><span class="identifier">any_cast</span></a><span class="special">(</span><a class="link" href="../boost/any.html" title="Class any">any</a> <span class="special">&&</span><span class="special">)</span><span class="special">;</span> 71 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> T<span class="special">></span> <span class="identifier">T</span> <a class="link" href="../boost/any_cast.html" title="Function any_cast"><span class="identifier">any_cast</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/any.html" title="Class any">any</a> <span class="special">&</span><span class="special">)</span><span class="special">;</span> 72 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> ValueType<span class="special">></span> <span class="keyword">const</span> <span class="identifier">ValueType</span> <span class="special">*</span> <a class="link" href="../boost/any_cast.html" title="Function any_cast"><span class="identifier">any_cast</span></a><span class="special">(</span><span class="keyword">const</span> <a class="link" href="../boost/any.html" title="Class any">any</a> <span class="special">*</span><span class="special">)</span><span class="special">;</span> 73 <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> ValueType<span class="special">></span> <span class="identifier">ValueType</span> <span class="special">*</span> <a class="link" href="../boost/any_cast.html" title="Function any_cast"><span class="identifier">any_cast</span></a><span class="special">(</span><a class="link" href="../boost/any.html" title="Class any">any</a> <span class="special">*</span><span class="special">)</span><span class="special">;</span> 74<span class="special">}</span></pre> 75</div> 76</div> 77<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 78<td align="left"></td> 79<td align="right"><div class="copyright-footer">Copyright © 2001 Kevlin Henney<br>Copyright © 2013-2020 Antony Polukhin<p>Distributed under the Boost Software License, Version 1.0. 80 (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at 81 <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 82 </p> 83</div></td> 84</tr></table> 85<hr> 86<div class="spirit-nav"> 87<a accesskey="p" href="s02.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../any.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/bad_any_cast.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 88</div> 89</body> 90</html> 91
