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150 lines
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="id-1.3.5.4"></a>Examples</h2></div></div></div>
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<p>The following code demonstrates the syntax for using
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implicit conversions to and copying of any objects:</p>
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<pre class="programlisting">
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#include <list>
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#include <boost/any.hpp>
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using <code class="computeroutput"><a class="link" href="../boost/any_cast.html" title="Function any_cast">boost::any_cast</a></code>;
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typedef std::list<<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code>> many;
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void append_int(many & values, int value)
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{
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<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> to_append = value;
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values.push_back(to_append);
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}
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void append_string(many & values, const std::string & value)
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{
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values.push_back(value);
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}
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void append_char_ptr(many & values, const char * value)
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{
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values.push_back(value);
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}
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void append_any(many & values, const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & value)
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{
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values.push_back(value);
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}
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void append_nothing(many & values)
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{
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values.push_back(<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code>());
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}
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</pre>
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<p>The following predicates follow on from the previous
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definitions and demonstrate the use of queries on any
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objects:</p>
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<pre class="programlisting">
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bool is_empty(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
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{
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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>();
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}
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bool is_int(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
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{
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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);
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}
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bool is_char_ptr(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
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{
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try
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{
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<code class="computeroutput"><a class="link" href="../boost/any_cast.html" title="Function any_cast">any_cast</a></code><const char *>(operand);
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return true;
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}
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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> &)
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{
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return false;
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}
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}
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bool is_string(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> & operand)
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{
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return <code class="computeroutput"><a class="link" href="../boost/any_cast.html" title="Function any_cast">any_cast</a></code><std::string>(&operand);
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}
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void count_all(many & values, std::ostream & out)
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{
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out << "#empty == "
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<< std::count_if(values.begin(), values.end(), is_empty) << std::endl;
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out << "#int == "
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<< std::count_if(values.begin(), values.end(), is_int) << std::endl;
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out << "#const char * == "
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<< std::count_if(values.begin(), values.end(), is_char_ptr) << std::endl;
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out << "#string == "
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<< std::count_if(values.begin(), values.end(), is_string) << std::endl;
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}
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</pre>
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<p>The following type, patterned after the OMG's Property Service, defines name-value pairs for arbitrary value types:</p>
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<pre class="programlisting">
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struct property
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{
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property();
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property(const std::string &, const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> &);
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std::string name;
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<code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">boost::any</a></code> value;
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};
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typedef std::list<property> properties;
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</pre>
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<p>The following base class demonstrates one approach to
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runtime polymorphism based callbacks that also require arbitrary
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argument types. The absence of virtual member templates requires
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that different solutions have different trade-offs in terms of
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efficiency, safety, and generality. Using a checked variant type
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offers one approach:</p>
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<pre class="programlisting">
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class consumer
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{
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public:
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virtual void notify(const <code class="computeroutput"><a class="link" href="../boost/any.html" title="Class any">any</a></code> &) = 0;
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...
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};
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</pre>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2001 Kevlin Henney<br>Copyright © 2013-2021 Antony Polukhin<p>Distributed under the Boost Software License, Version 1.0.
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(See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at
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<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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</p>
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</div></td>
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</tr></table>
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