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python/doc/tutorial/doc/auto_overloading.html
Joel de Guzman 600602f9dc Tutorial updates 
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2003-02-23 03:53:36 +00:00

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<html>
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<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
<title>Auto-Overloading</title>
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Auto-Overloading</b></font>
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<p>
It was mentioned in passing in the previous section that
<tt>BOOST_PYTHON_FUNCTION_OVERLOADS</tt> and <tt>BOOST_PYTHON_FUNCTION_OVERLOADS</tt>
can also be used for overloaded functions and member functions with a
common sequence of initial arguments. Here is an example:</p>
<code><pre>
<span class=keyword>void </span><span class=identifier>foo</span><span class=special>()
{
/*...*/
}
</span><span class=keyword>void </span><span class=identifier>foo</span><span class=special>(</span><span class=keyword>bool </span><span class=identifier>a</span><span class=special>)
{
/*...*/
}
</span><span class=keyword>void </span><span class=identifier>foo</span><span class=special>(</span><span class=keyword>bool </span><span class=identifier>a</span><span class=special>, </span><span class=keyword>int </span><span class=identifier>b</span><span class=special>)
{
/*...*/
}
</span><span class=keyword>void </span><span class=identifier>foo</span><span class=special>(</span><span class=keyword>bool </span><span class=identifier>a</span><span class=special>, </span><span class=keyword>int </span><span class=identifier>b</span><span class=special>, </span><span class=keyword>char </span><span class=identifier>c</span><span class=special>)
{
/*...*/
}
</span></pre></code>
<p>
Like in the previous section, we can generate thin wrappers for these
overloaded functions in one-shot:</p>
<code><pre>
<span class=identifier>BOOST_PYTHON_FUNCTION_OVERLOADS</span><span class=special>(</span><span class=identifier>foo_overloads</span><span class=special>, </span><span class=identifier>foo</span><span class=special>, </span><span class=number>0</span><span class=special>, </span><span class=number>3</span><span class=special>)
</span></pre></code>
<p>
Then...</p>
<code><pre>
<span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;foo&quot;</span><span class=special>, </span><span class=identifier>foo</span><span class=special>, </span><span class=identifier>foo_overloads</span><span class=special>());
</span></pre></code>
<p>
Notice though that we have a situation now where we have a minimum of zero
(0) arguments and a maximum of 3 arguments.</p>
<a name="manual_wrapping"></a><h2>Manual Wrapping</h2><p>
It is important to emphasize however that <b>the overloaded functions must
have a common sequence of initial arguments</b>. Otherwise, our scheme above
will not work. If this is not the case, we have to wrap our functions
<a href="overloading.html">
manually</a>.</p>
<p>
Actually, we can mix and match manual wrapping of overloaded functions and
automatic wrapping through <tt>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS</tt> and
its sister, <tt>BOOST_PYTHON_FUNCTION_OVERLOADS</tt>. Following up on our example
presented in the section <a href="overloading.html">
on overloading</a>, since the
first 4 overload functins have a common sequence of initial arguments, we
can use <tt>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS</tt> to automatically wrap the
first three of the <tt>def</tt>s and manually wrap just the last. Here's
how we'll do this:</p>
<code><pre>
<span class=identifier>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS</span><span class=special>(</span><span class=identifier>xf_overloads</span><span class=special>, </span><span class=identifier>f</span><span class=special>, </span><span class=number>1</span><span class=special>, </span><span class=number>4</span><span class=special>)
</span></pre></code>
<p>
Create a member function pointers as above for both X::f overloads:</p>
<code><pre>
<span class=keyword>bool </span><span class=special>(</span><span class=identifier>X</span><span class=special>::*</span><span class=identifier>fx1</span><span class=special>)(</span><span class=keyword>int</span><span class=special>, </span><span class=keyword>double</span><span class=special>, </span><span class=keyword>char</span><span class=special>) = &amp;</span><span class=identifier>X</span><span class=special>::</span><span class=identifier>f</span><span class=special>;
</span><span class=keyword>int </span><span class=special>(</span><span class=identifier>X</span><span class=special>::*</span><span class=identifier>fx2</span><span class=special>)(</span><span class=keyword>int</span><span class=special>, </span><span class=keyword>int</span><span class=special>, </span><span class=keyword>int</span><span class=special>) = &amp;</span><span class=identifier>X</span><span class=special>::</span><span class=identifier>f</span><span class=special>;
</span></pre></code>
<p>
Then...</p>
<code><pre>
<span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>fx1</span><span class=special>, </span><span class=identifier>xf_overloads</span><span class=special>());
.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>fx2</span><span class=special>)
</span></pre></code>
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<br>
<hr size="1"><p class="copyright">Copyright &copy; 2002-2003 David Abrahams<br>Copyright &copy; 2002-2003 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
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is provided &quot;as is&quot; without express or implied warranty, and with
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