tutorial update

[SVN r17512]
2026-01-23 17:52:17 +00:00 · 2003-02-18 18:44:16 +00:00
parent 472dc3bd41
commit ff9f262fac
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+<html>
+<head>
+<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
+<title>Overloading</title>
+<link rel="stylesheet" href="theme/style.css" type="text/css">
+<link rel="prev" href="default_arguments.html">
+<link rel="next" href="object_interface.html">
+</head>
+<body>
+<table width="100%" height="48" border="0" cellspacing="2">
+  <tr>
+    <td><img src="theme/c%2B%2Bboost.gif">
+    </td>
+    <td width="85%">
+      <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Overloading</b></font>
+    </td>
+  </tr>
+</table>
+<br>
+<table border="0">
+  <tr>
+    <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
+    <td width="30"><a href="default_arguments.html"><img src="theme/l_arr.gif" border="0"></a></td>
+    <td width="20"><a href="object_interface.html"><img src="theme/r_arr.gif" border="0"></a></td>
+   </tr>
+</table>
+<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.</p>
+<p>
+The following illustrates an alternate scheme for manually wrapping an
+overloaded member function instead of
+<tt>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS</tt>. Obviously, the same technique
+can be applied to wrapping overloaded non- member functions.</p>
+<p>
+We have here our C++ classes:</p>
+<code><pre>
+    <span class=keyword>struct </span><span class=identifier>X
+    </span><span class=special>{
+        </span><span class=keyword>bool </span><span class=identifier>f</span><span class=special>(</span><span class=keyword>int </span><span class=identifier>a</span><span class=special>, </span><span class=keyword>double </span><span class=identifier>b </span><span class=special>= </span><span class=number>0</span><span class=special>, </span><span class=keyword>char </span><span class=identifier>c </span><span class=special>= </span><span class=literal>'x'</span><span class=special>)
+        {
+            </span><span class=keyword>return </span><span class=keyword>true</span><span class=special>;
+        }
+
+        </span><span class=keyword>int </span><span class=identifier>f</span><span class=special>(</span><span class=keyword>int </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>int </span><span class=identifier>c</span><span class=special>)
+        {
+            </span><span class=keyword>return </span><span class=identifier>a </span><span class=special>+ </span><span class=identifier>b </span><span class=special>+ </span><span class=identifier>c</span><span class=special>;
+        };
+    };
+</span></pre></code>
+<p>
+Notice that class X has two overloaded functions with different signatures.
+The types of the arguments, and the return are totally different, unlike
+above where we have a common sequence of initial arguments.</p>
+<p>
+We shall start by introducing some member function pointer variables:</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>)              = &amp;</span><span class=identifier>X</span><span class=special>::</span><span class=identifier>f</span><span class=special>;
+    </span><span class=keyword>bool    </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>double</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>bool    </span><span class=special>(</span><span class=identifier>X</span><span class=special>::*</span><span class=identifier>fx3</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>fx4</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>
+The first three member function pointers take care of the first X::f
+overload. The one with default arguments. The last member function pointer
+takes care of the second X::f overload.</p>
+<p>
+With these in hand, we can proceed to define and wrap this for Python:</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>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><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>fx3</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>fx4</span><span class=special>)
+</span></pre></code>
+<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>. Since the first overload
+has default arguments, we can use <tt>BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS</tt>
+to automatically wrap the first three of the <tt>def</tt>s above 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>
+<table border="0">
+  <tr>
+    <td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
+    <td width="30"><a href="default_arguments.html"><img src="theme/l_arr.gif" border="0"></a></td>
+    <td width="20"><a href="object_interface.html"><img src="theme/r_arr.gif" border="0"></a></td>
+   </tr>
+</table>
+<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
+ is granted provided this copyright notice appears in all copies. This document
+ is provided &quot;as is&quot; without express or implied warranty, and with
+ no claim as to its suitability for any purpose. </font> </p>
+</body>
+</html>