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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>) |
| </p> |
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