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| <boost/python/return_internal_reference.hpp></title> |
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| <h3><a href="../../../../index.htm"><img height="86" width="277" |
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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_internal_reference.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_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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