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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Boost.Python - <boost/python/return_arg.hpp></title>
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3>
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<td valign="top">
<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
<h2 align="center">Header <boost/python/return_arg.hpp></h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#return_arg-spec">Class Template
<code>return_arg</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#return_arg-spec-synopsis">Class Template
<code>return_arg</code> synopsis</a></dt>
<dt><a href="#return_arg-spec-statics">Class
<code>return_arg</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#return_self-spec">Class Template
<code>return_self</code></a></dt>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>return_arg</code> and <code>return_self</code> instantiations are
models of <a href="CallPolicies.html">CallPolicies</a> which return the
specified argument parameter (usually <code>*this</code>) of a wrapped
(member) function.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="return_arg-spec"></a>Class template
<code>return_arg</code></h3>
<table border="1" summary="return_arg template parameters">
<caption>
<b><code>return_arg</code> template parameters</b>
</caption>
<tr>
<th>Parameter</th>
<th>Requirements</th>
<th>Description</th>
<th>Default</th>
</tr>
<tr>
<td><code>arg_pos</code></td>
<td>A positive compile-time constant of type
<code>std::size_t</code>.</td>
<td>the position of the argument to be returned.</td>
<td>1</td>
</tr>
<tr>
<td><code>Base</code></td>
<td>A model of <a href="CallPolicies.html">CallPolicies</a></td>
<td>Used for policy composition. Any <code>result_converter</code> it
supplies will be overridden by <code>return_arg</code>, but its
<code>precall</code> and <code>postcall</code> policies are composed
as described here <a href=
"CallPolicies.html#composition">CallPolicies</a>.</td>
<td><code><a href=
"default_call_policies.html#default_call_policies-spec">default_call_policies</a></code></td>
</tr>
</table>
<h4><a name="return_arg-spec-synopsis"></a>Class template
<code>return_arg</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template <size_t arg_pos=1, class Base = default_call_policies>
struct return_arg : Base
{
static PyObject* postcall(PyObject*, PyObject* result);
struct result_converter{ template <class T> struct apply; };
};
}}
</pre>
<h4><a name="return_arg-spec-statics"></a>Class <code>return_arg</code>
static functions</h4>
<pre>
PyObject* postcall(PyObject* args, PyObject* result);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code><a href=
"http://www.python.org/doc/2.2/api/tupleObjects.html#l2h-476">PyTuple_Check</a>(args)
!= 0</code> and <code>PyTuple_Size(args) != 0</code></dt>
<dt><b>Returns:</b> <code>PyTuple_GetItem(args,arg_pos-1)</code></dt>
</dl>
<h3><a name="return_self-spec"></a>Class template
<code>return_self</code></h3>
<h4>Class template <code>return_self</code> synopsis:</h4>
<pre>
namespace boost { namespace python
{
template <class Base = default_call_policies>
struct return_self
: return_arg<1,Base>
{};
}}
</pre>
<h2><a name="examples"></a>Example</h2>
<h3>C++ module definition</h3>
<pre>
#include <boost/python/module.hpp>
#include <boost/python/class.hpp>
#include <boost/python/return_arg.hpp>
struct Widget
{
Widget() :sensitive_(true){}
bool get_sensitive() const { return sensitive_; }
void set_sensitive(bool s) { this->sensitive_ = s; }
private:
bool sensitive_;
};
struct Label : Widget
{
Label() {}
std::string get_label() const { return label_; }
void set_label(const std::string &l){ label_ = l; }
private:
std::string label_;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(return_self_ext)
{
class_<widget>("Widget")
.def("sensitive", &Widget::get_sensitive)
.def("sensitive", &Widget::set_sensitive, return_self<>())
;
class_<Label, bases<Widget> >("Label")
.def("label", &Label::get_label)
.def("label", &Label::set_label, return_self<>())
;
}
</pre>
<h3>Python code</h3>
<pre>
>>> from return_self_ext import *
>>> l1 = Label().label("foo").sensitive(false)
>>> l2 = Label().sensitive(false).label("foo")
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
19 July, 2003 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>© Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> and Nikolay
Mladenov 2003. </i></p>
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