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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="idp135780768"></a>Examples</h2></div></div></div>
<p>The following code demonstrates the syntax for using
implicit conversions to and copying of any objects:</p>
<pre class="programlisting">
#include <list>
#include <boost/any.hpp>
using <code class="computeroutput"><a class="link" href="../boost/any_cast_idp424495968.html" title="Function any_cast">boost::any_cast</a></code>;
typedef std::list<<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code>> many;
void append_int(many & values, int value)
{
<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> to_append = value;
values.push_back(to_append);
}
void append_string(many & values, const std::string & value)
{
values.push_back(value);
}
void append_char_ptr(many & values, const char * value)
{
values.push_back(value);
}
void append_any(many & values, const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & value)
{
values.push_back(value);
}
void append_nothing(many & values)
{
values.push_back(<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code>());
}
</pre>
<p>The following predicates follow on from the previous
definitions and demonstrate the use of queries on any
objects:</p>
<pre class="programlisting">
bool is_empty(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
{
return operand.<code class="computeroutput"><a class="link" href="../boost/any.html#idp424483808-bb">empty</a></code>();
}
bool is_int(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
{
return operand.<code class="computeroutput"><a class="link" href="../boost/any.html#idp424486720-bb">type</a></code>() == typeid(int);
}
bool is_char_ptr(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
{
try
{
<code class="computeroutput"><a class="link" href="../boost/any_cast_idp424495968.html" title="Function any_cast">any_cast</a></code><const char *>(operand);
return true;
}
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> &)
{
return false;
}
}
bool is_string(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
{
return <code class="computeroutput"><a class="link" href="../boost/any_cast_idp424495968.html" title="Function any_cast">any_cast</a></code><std::string>(&operand);
}
void count_all(many & values, std::ostream & out)
{
out << "#empty == "
<< std::count_if(values.begin(), values.end(), is_empty) << std::endl;
out << "#int == "
<< std::count_if(values.begin(), values.end(), is_int) << std::endl;
out << "#const char * == "
<< std::count_if(values.begin(), values.end(), is_char_ptr) << std::endl;
out << "#string == "
<< std::count_if(values.begin(), values.end(), is_string) << std::endl;
}
</pre>
<p>The following type, patterned after the OMG's Property Service, defines name-value pairs for arbitrary value types:</p>
<pre class="programlisting">
struct property
{
property();
property(const std::string &, const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> &);
std::string name;
<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> value;
};
typedef std::list<property> properties;
</pre>
<p>The following base class demonstrates one approach to
runtime polymorphism based callbacks that also require arbitrary
argument types. The absence of virtual member templates requires
that different solutions have different trade-offs in terms of
efficiency, safety, and generality. Using a checked variant type
offers one approach:</p>
<pre class="programlisting">
class consumer
{
public:
virtual void notify(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">any</a></code> &) = 0;
...
};
</pre>
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<td align="right"><div class="copyright-footer">Copyright © 2001 Kevlin Henney<p>Distributed under the Boost Software License, Version 1.0.
(See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at
<a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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