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>Examples</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="../any.html" title="Chapter 4. Boost.Any"> 11<link rel="next" href="reference.html" title="Reference"> 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="../any.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="reference.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="id-1.3.5.4"></a>Examples</h2></div></div></div> 29<p>The following code demonstrates the syntax for using 30 implicit conversions to and copying of any objects:</p> 31<pre class="programlisting"> 32#include <list> 33#include <boost/any.hpp> 34 35using <code class="computeroutput"><a class="link" href="../boost/any_cast.html" title="Function any_cast">boost::any_cast</a></code>; 36typedef std::list<<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code>> many; 37 38void append_int(many & values, int value) 39{ 40 <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> to_append = value; 41 values.push_back(to_append); 42} 43 44void append_string(many & values, const std::string & value) 45{ 46 values.push_back(value); 47} 48 49void append_char_ptr(many & values, const char * value) 50{ 51 values.push_back(value); 52} 53 54void append_any(many & values, const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & value) 55{ 56 values.push_back(value); 57} 58 59void append_nothing(many & values) 60{ 61 values.push_back(<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code>()); 62} 63</pre> 64<p>The following predicates follow on from the previous 65 definitions and demonstrate the use of queries on any 66 objects:</p> 67<pre class="programlisting"> 68bool is_empty(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand) 69{ 70 return operand.<code class="computeroutput"><a class="link" href="../boost/any.html#id-1_3_5_5_2_1_2_13_1-bb">empty</a></code>(); 71} 72 73bool is_int(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand) 74{ 75 return operand.<code class="computeroutput"><a class="link" href="../boost/any.html#id-1_3_5_5_2_1_2_13_2-bb">type</a></code>() == typeid(int); 76} 77 78bool is_char_ptr(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand) 79{ 80 try 81 { 82 <code class="computeroutput"><a class="link" href="../boost/any_cast.html" title="Function any_cast">any_cast</a></code><const char *>(operand); 83 return true; 84 } 85 catch(const <code class="computeroutput"><a class="link" href="../boost/bad_any_cast.html" title="Class bad_any_cast">boost::bad_any_cast</a></code> &) 86 { 87 return false; 88 } 89} 90 91bool is_string(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand) 92{ 93 return <code class="computeroutput"><a class="link" href="../boost/any_cast.html" title="Function any_cast">any_cast</a></code><std::string>(&operand); 94} 95 96void count_all(many & values, std::ostream & out) 97{ 98 out << "#empty == " 99 << std::count_if(values.begin(), values.end(), is_empty) << std::endl; 100 out << "#int == " 101 << std::count_if(values.begin(), values.end(), is_int) << std::endl; 102 out << "#const char * == " 103 << std::count_if(values.begin(), values.end(), is_char_ptr) << std::endl; 104 out << "#string == " 105 << std::count_if(values.begin(), values.end(), is_string) << std::endl; 106} 107</pre> 108<p>The following type, patterned after the OMG's Property Service, defines name-value pairs for arbitrary value types:</p> 109<pre class="programlisting"> 110struct property 111{ 112 property(); 113 property(const std::string &, const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> &); 114 115 std::string name; 116 <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> value; 117}; 118 119typedef std::list<property> properties; 120</pre> 121<p>The following base class demonstrates one approach to 122 runtime polymorphism based callbacks that also require arbitrary 123 argument types. The absence of virtual member templates requires 124 that different solutions have different trade-offs in terms of 125 efficiency, safety, and generality. Using a checked variant type 126 offers one approach:</p> 127<pre class="programlisting"> 128class consumer 129{ 130public: 131 virtual void notify(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">any</a></code> &) = 0; 132 ... 133}; 134</pre> 135</div> 136<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 137<td align="left"></td> 138<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. 139 (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at 140 <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 141 </p> 142</div></td> 143</tr></table> 144<hr> 145<div class="spirit-nav"> 146<a accesskey="p" href="../any.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="reference.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 147</div> 148</body> 149</html> 150
