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Dave Abrahams 921e306b9a Fix license/copyright 
[SVN r35234]
2006-09-20 21:59:03 +00:00

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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Wrappers</b></font>
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<p>
Suppose you have this function:</p>
<code><pre>
<span class=identifier>std</span><span class=special>::</span><span class=identifier>vector</span><span class=special>&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&gt; </span><span class=identifier>names</span><span class=special>();
</span></pre></code>
<p>
But you don't want to <a href="../../doc/v2/faq.html#question2">
to export std::vector&lt;std::string&gt;</a>,
you want this function to return a python list of strings. <a href="../../index.html">
Boost.Python</a> has
excellent support for things like that:</p>
<code><pre>
<span class=identifier>list </span><span class=identifier>names_wrapper</span><span class=special>()
{
</span><span class=identifier>list </span><span class=identifier>result</span><span class=special>;
// </span><span class=identifier>call </span><span class=identifier>original </span><span class=identifier>function
</span><span class=identifier>vector</span><span class=special>&lt;</span><span class=identifier>string</span><span class=special>&gt; </span><span class=identifier>v </span><span class=special>= </span><span class=identifier>names</span><span class=special>();
// </span><span class=identifier>put </span><span class=identifier>all </span><span class=identifier>the </span><span class=identifier>strings </span><span class=identifier>inside </span><span class=identifier>the </span><span class=identifier>python </span><span class=identifier>list
</span><span class=identifier>vector</span><span class=special>&lt;</span><span class=identifier>string</span><span class=special>&gt;::</span><span class=identifier>iterator </span><span class=identifier>it</span><span class=special>;
</span><span class=keyword>for </span><span class=special>(</span><span class=identifier>it </span><span class=special>= </span><span class=identifier>v</span><span class=special>.</span><span class=identifier>begin</span><span class=special>(); </span><span class=identifier>it </span><span class=special>!= </span><span class=identifier>v</span><span class=special>.</span><span class=identifier>end</span><span class=special>(); ++</span><span class=identifier>it</span><span class=special>){
</span><span class=identifier>result</span><span class=special>.</span><span class=identifier>append</span><span class=special>(*</span><span class=identifier>it</span><span class=special>);
}
</span><span class=keyword>return </span><span class=identifier>result</span><span class=special>;
}
</span><span class=identifier>BOOST_PYTHON_MODULE</span><span class=special>(</span><span class=identifier>test</span><span class=special>)
{
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;names&quot;</span><span class=special>, &amp;</span><span class=identifier>names_wrapper</span><span class=special>);
}
</span></pre></code>
<p>
Nice heh? Pyste supports this mechanism too. You declare the <tt>names_wrapper</tt>
function in a header named &quot;<tt>test_wrappers.h</tt>&quot; and in the interface file:</p>
<code><pre>
<span class=identifier>Include</span><span class=special>(</span><span class=string>&quot;test_wrappers.h&quot;</span><span class=special>)
</span><span class=identifier>names </span><span class=special>= </span><span class=identifier>Function</span><span class=special>(</span><span class=string>&quot;names&quot;</span><span class=special>, </span><span class=string>&quot;test.h&quot;</span><span class=special>)
</span><span class=identifier>set_wrapper</span><span class=special>(</span><span class=identifier>names</span><span class=special>, </span><span class=string>&quot;names_wrapper&quot;</span><span class=special>)
</span></pre></code>
<p>
You can optionally declare the function in the interface file itself:</p>
<code><pre>
<span class=identifier>names_wrapper </span><span class=special>= </span><span class=identifier>Wrapper</span><span class=special>(</span><span class=string>&quot;names_wrapper&quot;</span><span class=special>,
</span><span class=string>&quot;&quot;</span><span class=string>&quot;
list names_wrapper()
{
// code to call name() and convert the vector to a list...
}
&quot;</span><span class=string>&quot;&quot;</span><span class=special>)
</span><span class=identifier>names </span><span class=special>= </span><span class=identifier>Function</span><span class=special>(</span><span class=string>&quot;names&quot;</span><span class=special>, </span><span class=string>&quot;test.h&quot;</span><span class=special>)
</span><span class=identifier>set_wrapper</span><span class=special>(</span><span class=identifier>names</span><span class=special>, </span><span class=identifier>names_wrapper</span><span class=special>)
</span></pre></code>
<p>
The same mechanism can be used with member functions too. Just remember that
the first parameter of wrappers for member functions is a pointer to the
class, as in:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>C
</span><span class=special>{
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>vector</span><span class=special>&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&gt; </span><span class=identifier>names</span><span class=special>();
}
</span><span class=identifier>list </span><span class=identifier>names_wrapper</span><span class=special>(</span><span class=identifier>C</span><span class=special>* </span><span class=identifier>c</span><span class=special>)
{
// </span><span class=identifier>same </span><span class=identifier>as </span><span class=identifier>before</span><span class=special>, </span><span class=identifier>calling </span><span class=identifier>c</span><span class=special>-&gt;</span><span class=identifier>names</span><span class=special>() </span><span class=keyword>and </span><span class=identifier>converting </span><span class=identifier>result </span><span class=identifier>to </span><span class=identifier>a </span><span class=identifier>list
</span><span class=special>}
</span></pre></code>
<p>
And then in the interface file:</p>
<code><pre>
<span class=identifier>C </span><span class=special>= </span><span class=identifier>Class</span><span class=special>(</span><span class=string>&quot;C&quot;</span><span class=special>, </span><span class=string>&quot;test.h&quot;</span><span class=special>)
</span><span class=identifier>set_wrapper</span><span class=special>(</span><span class=identifier>C</span><span class=special>.</span><span class=identifier>names</span><span class=special>, </span><span class=string>&quot;names_wrapper&quot;</span><span class=special>)
</span></pre></code>
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<td class="note_box">
<img src="theme/note.gif"></img>Even though <a href="../../index.html">
Boost.Python</a> accepts either a pointer or a
reference to the class in wrappers for member functions as the first parameter,
Pyste expects them to be a <b>pointer</b>. Doing otherwise will prevent your
code to compile when you set a wrapper for a virtual member function.
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<hr size="1"><p class="copyright">Copyright &copy; 2003 Bruno da Silva de Oliveira<br>Copyright &copy; 2002-2003 Joel de Guzman<br><br>
<font size="2">Distributed under
the Boost Software License, Version 1.0. (See accompanying file
LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) </font> </p>
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