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| <div class="titlepage"><div><div><h2 class="title" style="clear: both"> | |
| <a name="id1010264"></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.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#id424525-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#id424550-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.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.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="left"></td> | |
| <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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