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| <title>Boost.Python - <boost/python/ptr.hpp></title> |
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| <td valign="top"> |
| <h1 align="center"><a href="../index.html">Boost.Python</a></h1> |
| |
| <h2 align="center">Header <boost/python/ptr.hpp></h2> |
| </table> |
| <hr> |
| |
| <h2>Contents</h2> |
| |
| <dl class="page-index"> |
| <dt><a href="#introduction">Introduction</a> |
| |
| <dt><a href="#functions">Functions</a> |
| <dd> |
| <dl class="page-index"> |
| <dt><a href="#ptr-spec">ptr</a> |
| </dl> |
| |
| <dt><a href="#classes">Classes</a> |
| <dd> |
| <dl class="page-index"> |
| <dt><a href="#pointer_wrapper-spec">Class template <code>pointer_wrapper</code></a> |
| |
| <dd> |
| <dl class="page-index"> |
| <dt><a href="#pointer_wrapper-spec-synopsis">Class template <code>pointer_wrapper</code> synopsis</a> |
| |
| <dt><a href="#pointer_wrapper-spec-types">Class |
| <code>pointer_wrapper</code> types</a> |
| |
| <dt><a href="#pointer_wrapper-spec-ctors">Class |
| <code>pointer_wrapper</code> constructors and destructor</a> |
| |
| <dt><a href="#pointer_wrapper-spec-observers">Class |
| <code>pointer_wrapper</code> observer functions</a> |
| |
| </dl> |
| </dl> |
| |
| <dt><a href="#metafunctions">Metafunctions</a> |
| <dd> |
| <dl class="page-index"> |
| <dt><a href="#is_pointer_wrapper-spec">Class template <code>is_pointer_wrapper</code></a> |
| |
| <dd> |
| <dl class="page-index"> |
| <dt><a href="#is_pointer_wrapper-spec-synopsis">Class template <code>is_pointer_wrapper</code> synopsis</a> |
| </dl> |
| |
| |
| <dt><a href="#unwrap_pointer-spec">Class template <code>unwrap_pointer</code></a> |
| |
| <dd> |
| <dl class="page-index"> |
| <dt><a href="#unwrap_pointer-spec-synopsis">Class template <code>unwrap_pointer</code> synopsis</a> |
| </dl> |
| |
| </dl> |
| |
| |
| <dt><a href="#examples">Example(s)</a> |
| </dl> |
| <hr> |
| |
| <h2><a name="introduction"></a>Introduction</h2> |
| |
| <p><code><boost/python/ptr.hpp></code> defines the |
| <code>ptr()</code> function template, which allows users to |
| specify how to convert C++ pointer values to python in the context |
| of implementing overridable virtual functions, invoking Python |
| callable objects, or explicitly converting C++ objects to |
| Python. Normally, when passing pointers to Python callbacks, the |
| pointee is copied to ensure that the Python object |
| never holds a dangling reference. To specify that the new Python |
| object should merely contain a copy of a pointer <code>p</code>, |
| the user can pass <code><a href="#ptr-spec">ptr</a>(p)</code> instead of passing |
| <code>p</code> directly. This interface is meant to mirror the use |
| of <a href="../../../bind/ref.html"><code>boost::ref()</code></a>, |
| which can be similarly used to prevent copying of referents. |
| |
| <p><code>ptr(p)</code> returns an instance of <code><a |
| href="#pointer_wrapper-spec">pointer_wrapper<></a></code>, which |
| can be detected using the <code><a |
| href="#is_pointer_wrapper-spec">is_pointer_wrapper<></a></code> |
| metafunction; <code><a |
| href="#unwrap_pointer-spec">unwrap_pointer<></a></code> is a |
| metafunction which extracts the original pointer type from a |
| <code>pointer_wrapper<></code>. These classes can be thought |
| of as implementation details. |
| |
| <h2><a name="functions"></a>Functions</h2> |
| <pre> |
| |
| <a name="ptr-spec">template <class T></a> |
| pointer_wrapper<T> ptr(T x); |
| </pre> |
| |
| <dl class="ptr-semantics"> |
| <dt><b>Requires:</b> <code>T</code> is a pointer type. |
| |
| <dt><b>Returns:</b> <code><a href="#pointer_wrapper-spec">pointer_wrapper</a><T>(x)</code> |
| |
| <dt><b>Throws:</b> nothing. |
| </dl> |
| |
| <h2><a name="classes"></a>Classes</h2> |
| |
| <h3><a name="pointer_wrapper-spec"></a>Class template <code>pointer_wrapper</code></h3> |
| |
| <p>A "type envelope" which is returned by <a |
| href="#ptr-spec">ptr()</a>, used to indicate reference semantics |
| for pointers passed to Python callbacks. |
| |
| <h4><a name="pointer_wrapper-spec-synopsis"></a>Class |
| <code>pointer_wrapper</code> synopsis</h4> |
| <pre> |
| namespace boost { namespace python |
| { |
| template<class Ptr> class pointer_wrapper |
| { |
| public: |
| typedef Ptr type; |
| |
| explicit pointer_wrapper(Ptr x); |
| operator Ptr() const; |
| Ptr get() const; |
| }; |
| }} |
| </pre> |
| |
| <h4><a name="pointer_wrapper-spec-types"></a>Class template <code>pointer_wrapper</code> types</h4> |
| <pre> |
| typedef Ptr type; |
| </pre> |
| The type of the pointer being wrapped. |
| |
| <h4><a name="pointer_wrapper-spec-ctors"></a>Class template <code>pointer_wrapper</code> constructors and |
| destructor</h4> |
| <pre> |
| explicit pointer_wrapper(Ptr x); |
| </pre> |
| |
| <dl class="function-semantics"> |
| <dt><b>Requires:</b> <code>Ptr</code> is a pointer type. |
| |
| <dt><b>Effects:</b> Stores <code>x</code> in a the <code>pointer_wrapper<></code>. |
| <dt><b>Throws:</b> nothing. |
| </dl> |
| |
| <h4><a name="pointer_wrapper-spec-observers"></a>Class template <code>pointer_wrapper</code> observer |
| functions</h4> |
| <pre> |
| operator Ptr() const; |
| Ptr get() const; |
| </pre> |
| |
| <dl class="function-semantics"> |
| <dt><b>Returns:</b> a copy of the stored pointer. |
| <dt><b>Rationale:</b> <code>pointer_wrapper</code> is intended |
| to be a stand-in for the actual pointer type, but sometimes it's |
| better to have an explicit way to retrieve the pointer. |
| </dl> |
| |
| <h2><a name="metafunctions"></a>Metafunctions</h2> |
| |
| <h3><a name="is_pointer_wrapper-spec"></a>Class template <code>is_pointer_wrapper</code></h3> |
| |
| <p>A unary metafunction whose <code>value</code> is true iff its |
| argument is a <code>pointer_wrapper<></code>. |
| |
| <h4><a name="is_pointer_wrapper-spec-synopsis"></a>Class template <code>is_pointer_wrapper</code> synopsis</h4> |
| <pre> |
| namespace boost { namespace python |
| { |
| template<class T> class is_pointer_wrapper |
| { |
| static <i>unspecified</i> value = ...; |
| }; |
| }} |
| </pre> |
| |
| |
| <dl class="metafunction-semantics"> |
| <dt><b>Returns:</b> <code>true</code> iff <code>T</code> is a |
| specialization of |
| <code>pointer_wrapper<></code>. |
| <dt><code>value</code> is an integral constant convertible to bool of |
| unspecified type |
| |
| </dl> |
| |
| <h3><a name="unwrap_pointer-spec"></a>Class template <code>unwrap_pointer</code></h3> |
| |
| A unary metafunction which extracts the wrapped pointer type from a |
| specialization of <code>pointer_wrapper<></code>. |
| |
| <h4><a name="unwrap_pointer-spec-synopsis"></a>Class template <code>unwrap_pointer</code> synopsis</h4> |
| <pre> |
| namespace boost { namespace python |
| { |
| template<class T> class unwrap_pointer |
| { |
| typedef <i>unspecified</i> type; |
| }; |
| }} |
| </pre> |
| |
| <dl class="metafunction-semantics"> |
| <dt><b>Returns:</b> <code>T::type</code> if <code>T</code> is a |
| specialization of |
| <code>pointer_wrapper<></code>, <code>T</code> otherwise |
| </dl> |
| |
| |
| <h2><a name="examples"></a>Example(s)</h2> |
| |
| This example illustrates the use of <code>ptr()</code> to prevent an |
| object from being copied: |
| <pre> |
| #include <boost/python/call.hpp> |
| #include <boost/python/ptr.hpp> |
| |
| class expensive_to_copy |
| { |
| ... |
| }; |
| |
| void pass_as_arg(expensive_to_copy* x, PyObject* f) |
| { |
| // call the Python function f, passing a Python object built around |
| // which refers to *x by-pointer. |
| // |
| // *** Note: ensuring that *x outlives the argument to f() is *** |
| // *** up to the user! Failure to do so could result in a crash! *** |
| |
| boost::python::call<void>(f, ptr(x)); |
| } |
| ... |
| </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><i>© Copyright <a href="http://www.boost.org/people/dave_abrahams.htm">Dave |
| Abrahams</a> 2002. </i> Distributed |
| under the Boost Software License, Version 1.0. (See accompanying file |
| LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)</p> |
| |