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<title>Boost.Python - <boost/python/handle.hpp></title>
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<h1 class="c1"><a href="../index.html">Boost.Python</a></h1>
<h2 class="c2">Header <boost/python/handle.hpp></h2>
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<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="#handle-spec">Class template
<code>handle</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#handle-spec-synopsis">Class <code>handle</code>
synopsis</a></dt>
<dt><a href="#handle-spec-ctors">Class <code>handle</code>
constructors and destructor</a></dt>
<dt><a href="#handle-spec-modifiers">Class <code>handle</code>
modifier functions</a></dt>
<dt><a href="#handle-spec-observers">Class <code>handle</code>
observer functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#borrowed-spec"><code>borrowed</code></a></dt>
<dt><a href="#allow_null-spec"><code>allow_null</code></a></dt>
</dl>
</dd>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><boost/python/handle.hpp></code> provides
<code>class template handle</code>, a smart pointer for
managing reference-counted Python objects.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="handle-spec"></a>Class template <code>handle</code></h3>
<p><code>handle</code> is a smart pointer to a Python object type; it
holds a pointer of type <code>T*</code>, where T is its template
parameter. <code>T</code> must be either a type derived from
<code>PyObject</code> or a <a href="definitions.html#POD">POD</a> type
whose initial <code>sizeof(PyObject)</code> bytes are layout-compatible
with <code>PyObject</code>. Use <code>handle<></code> at the
boundary between the Python/'C' API and high-level code; prefer <code><a
href="object.html#object-spec">object</a></code> for a generalized
interface to Python objects.</p>
<p><a name="upcast"></a>In this document, the term "upcast" refers to an
operation which converts a pointer <code>Y*</code> to a base class
pointer <code>T*</code> via <code>static_cast<T*></code> if
<code>Y</code> is derived from <code>T</code>, or via C-style cast
<code>(T*)</code> if it is not. However, in the latter case the "upcast"
is ill-formed if the initial <code>sizeof(PyObject)</code> bytes of
<code>Y</code> are not layout-compatible with <code>PyObject</code>.</p>
<h4><a name="handle-spec-synopsis"></a>Class template handle
synopsis</h4>
<pre>
namespace boost { namespace python
{
template <class T>
class handle
{
typedef <i>unspecified-member-function-pointer</i> bool_type;
public: // types
typedef T element_type;
public: // member functions
~handle();
template <class Y>
explicit handle(detail::borrowed<null_ok<Y> >* p);
template <class Y>
explicit handle(null_ok<detail::borrowed<Y> >* p);
template <class Y>
explicit handle(detail::borrowed<Y>* p);
template <class Y>
explicit handle(null_ok<Y>* p);
template <class Y>
explicit handle(Y* p);
handle();
handle& operator=(handle const& r);
template<typename Y>
handle& operator=(handle<Y> const & r); // never throws
template <typename Y>
handle(handle<Y> const& r);
handle(handle const& r);
T* operator-> () const;
T& operator* () const;
T* get() const;
void reset();
T* release();
operator bool_type() const; // never throws
private:
T* m_p;
};
template <class T> struct null_ok;
namespace detail { template <class T> struct borrowed; }
}}
</pre>
<h4><a name="handle-spec-ctors">Class <code>handle</code> constructors
and destructor</a></h4>
<pre>
virtual ~handle();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XDECREF(</code><i>upcast</i><code><PyObject*>(m_p))</code></dt>
</dl>
<pre>
template <class Y>
explicit handle(detail::borrowed<null_ok<Y> >* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XINCREF(</code><i>upcast</i><code><PyObject*>(p));
m_p = </code><i>upcast</i><code><T*>(p);</code></dt>
</dl>
<pre>
template <class Y>
explicit handle(null_ok<detail::borrowed<Y> >* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XINCREF(</code><i>upcast</i><code><PyObject*>(p));
m_p = </code><i>upcast</i><code><T*>(p);</code></dt>
</dl>
<pre>
template <class Y>
explicit handle(detail::borrowed<Y>* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XINCREF(</code><i>upcast</i><code><PyObject*>(p));
m_p = </code><i>upcast</i><code><T*>(<a href=
"errors.html#expect_non_null-spec">expect_non_null</a>(p));</code></dt>
</dl>
<pre>
template <class Y>
explicit handle(null_ok<Y>* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>m_p = </code><i>upcast</i><code><T*>(p);</code></dt>
</dl>
<pre>
template <class Y>
explicit handle(Y* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>m_p = </code><i>upcast</i><code><T*>(<a href=
"errors.html#expect_non_null-spec">expect_non_null</a>(p));</code></dt>
</dl>
<pre>
handle();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> <code>m_p = 0;</code></dt>
</dl>
<pre>
template <typename Y>
handle(handle<Y> const& r);
handle(handle const& r);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>m_p = r.m_p; Py_XINCREF(</code><i>upcast</i><code><PyObject*>(m_p));</code></dt>
</dl>
<h4><a name="handle-spec-modifiers">Class <code>handle</code>
modifiers</a></h4>
<pre>
handle& operator=(handle const& r);
template<typename Y>
handle& operator=(handle<Y> const & r); // never throws
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XINCREF(</code><i>upcast</i><code><PyObject*>(r.m_p)); Py_XDECREF(</code><i>
upcast</i><code><PyObject*>(m_p)); m_p = r.m_p;</code></dt>
</dl>
<pre>
T* release();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> <code>T* x = m_p; m_p = 0;return
x;</code></dt>
</dl>
<pre>
void reset();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>*this = handle<T>();</code></dt>
</dl>
<h4><a name="handle-spec-observers">Class <code>handle</code>
observers</a></h4>
<pre>
T* operator-> () const;
T* get() const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>m_p;</code></dt>
</dl>
<pre>
T& operator* () const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>*m_p;</code></dt>
</dl>
<pre>
operator bool_type() const; // never throws
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> 0 if <code>m_p == 0</code>, a pointer
convertible to <code>true</code> otherwise.</dt>
</dl>
<h2><a name="functions"></a>Functions</h2>
<h3><a name="borrowed-spec"></a><code>borrowed</code></h3>
<pre>
template <class T>
detail::borrowed<T>* borrowed(T* p)
{
return (detail::borrowed<T>*)p;
}
</pre>
<h3><a name="allow_null-spec"></a><code>allow_null</code></h3>
<pre>
template <class T>
null_ok<T>* allow_null(T* p)
{
return (null_ok<T>*)p;
}
</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 class="c4">© Copyright <a href=
"http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002
.</p>
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