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<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
<h2 align="center">Header
<boost/python/return_internal_reference.hpp></h2>
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<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_internal_reference-spec">Class Template
<code>return_internal_reference</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#return_internal_reference-spec-synopsis">Class
Template <code>return_internal_reference</code>
synopsis</a></dt>
<dt><a href="#return_internal_reference-spec-statics">Class
<code>return_internal_reference</code> static
functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>return_internal_reference</code> instantiations are models of <a
href="CallPolicies.html">CallPolicies</a> which allow pointers and
references to objects held internally by a free or member function
argument or from the target of a member function to be returned safely
without making a copy of the referent. The default for its first template
argument handles the common case where the containing object is the
target (<code>*this</code>) of a wrapped member function.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="return_internal_reference-spec"></a>Class template
<code>return_internal_reference</code></h3>
<table border="1" summary=
"return_internal_reference template parameters">
<caption>
<b><code>return_internal_reference</code> template parameters</b>
</caption>
<tr>
<th>Parameter</th>
<th>Requirements</th>
<th>Description</th>
<th>Default</th>
</tr>
<tr>
<td><code>owner_arg</code></td>
<td>A positive compile-time constant of type
<code>std::size_t</code>.</td>
<td>The index of the parameter which contains the object to which the
reference or pointer is being returned. If used to wrap a member
function, parameter 1 is the target object (<code>*this</code>). Note
that if the target Python object type doesn't support weak
references, a Python <code>TypeError</code> exception will be raised
when the function being wrapped is called.</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_internal_reference</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_internal_reference-spec-synopsis"></a>Class template
<code>return_internal_reference</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template <std::size_t owner_arg = 1, class Base = default_call_policies>
struct return_internal_reference : Base
{
static PyObject* postcall(PyObject*, PyObject* result);
typedef <a href=
"reference_existing_object.html#reference_existing_object-spec">reference_existing_object</a> result_converter;
};
}}
</pre>
<h4><a name="return_internal_reference-spec-statics"></a>Class
<code>return_internal_reference</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></dt>
<dt><b>Returns:</b> <code><a href=
"with_custodian_and_ward.html#with_custodian_and_ward_postcall-spec-statics">
with_custodian_and_ward_postcall::postcall(args,
result)</a></code></dt>
</dl>
<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_internal_reference.hpp>
class Bar
{
public:
Bar(int x) : x(x) {}
int get_x() const { return x; }
void set_x(int x) { this->x = x; }
private:
int x;
};
class Foo
{
public:
Foo(int x) : b(x) {}
// Returns an internal reference
Bar const& get_bar() const { return b; }
private:
Bar b;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(internal_refs)
{
class_<Bar>("Bar", init<int>())
.def("get_x", &Bar::get_x)
.def("set_x", &Bar::set_x)
;
class_<Foo>("Foo", init<int>())
.def("get_bar", &Foo::get_bar
, return_internal_reference<>())
;
}
</pre>
<h3>Python code</h3>
<pre>
>>> from internal_refs import *
>>> f = Foo(3)
>>> b1 = f.get_bar()
>>> b2 = f.get_bar()
>>> b1.get_x()
3
>>> b2.get_x()
3
>>> b1.set_x(42)
>>> b2.get_x()
42
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
13 November, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>© Copyright <a href=
"http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
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