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<title>Boost.Python - <boost/python/init.hpp></title>
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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">Headers <boost/python/init.hpp></h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href=
"#init-expressions"><em>init-expressions</em></a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#init-spec">Class template <code>init</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#init-spec-synopsis">Class template
<code>init</code> synopsis</a></dt>
<dt><a href="#init-spec-ctors">Class <code>init</code>
constructors</a></dt>
</dl>
</dd>
<dt><a href="#optional-spec">Class template
<code>optional</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#optional-spec-synopsis">Class template
<code>optional</code> synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><boost/python/init.hpp></code> defines the interface for
exposing C++ constructors to Python as extension class
<code>__init__</code> functions.</p>
<h2><a name="init-expressions"><em>init-expressions</em></a></h2>
An <em>init-expression</em> is used to describe a family of
<code>__init__</code> methods to be generated for an extension class, and
the result has the following properties:
<blockquote>
<dl class="properties">
<dt><b>docstring:</b> An <a href="definitions.html#ntbs">ntbs</a>
whose value will bound to the method's <code>__doc__</code>
attribute</dt>
<dt><b>keywords:</b> A <a href=
"args.html#keyword-expression">keyword-expression</a> which will be
used to name (a trailing subsequence of) the arguments to the
generated <code>__init__</code> function(s).</dt>
<dt><b>call policies:</b> An instance of a model of <a href=
"CallPolicies.html">CallPolicies</a>.</dt>
<dt><b>argument types:</b> An MPL sequence of C++ argument types
which will be used to construct the wrapped C++ object. An init
expression has one or more
<b>valid prefixes</b> which are given by a sequence of
prefixes of its argument types.</dt>
</dl>
</blockquote>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="init-spec"></a>Class template <code>init<T1 =</code>
<i>unspecified</i><code>, T2 =</code>
<i>unspecified</i><code>,</code>...<code>Tn</code> =
<i>unspecified</i><code>></code></h3>
<p>A <a href="../../../mpl/doc/refmanual/forward-sequence.html">MPL sequence</a> which
can be used to specify a family of one or more <code>__init__</code>
functions. Only the last <code>T</code><i><small>i</small></i> supplied
may be an instantiation of <a href=
"#optional-spec"><code>optional</code></a><code><</code>...<code>></code>.</p>
<h4><a name="init-spec-synopsis"></a>Class template <code>init</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
template <T1 = <i>unspecified</i>,...T<i>n</i> = <i>unspecified</i>>
struct init
{
init(char const* doc = 0);
template <class Keywords> init(Keywords const& kw, char const* doc = 0);
template <class Keywords> init(char const* doc, Keywords const& kw);
template <class CallPolicies>
<em>unspecified</em> operator[](CallPolicies const& policies) const
};
}}
</pre>
<h4><a name="init-spec-ctors"></a>Class template <code>init</code>
constructors</h4>
<pre>
init(char const* doc = 0);
template <class Keywords> init(Keywords const& kw, char const* doc = 0);
template <class Keywords> init(char const* doc, Keywords const& kw);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> If supplied, <code>doc</code> is an <a href=
"definitions.html#ntbs">ntbs</a>. If supplied, <code>kw</code> is the
result of a <a href="args.html#keyword-expression"></a></dt>
<dt><b>Effects:</b> The result is an <em>init-expression</em> whose
<em>docstring</em> is <code>doc</code> and whose <em>keywords</em> are
a reference to <code>kw</code>. If the first form is used, the
resulting expression's <em>keywords</em> are empty. The expression's
<em>call policies</em> are an instance of <a href=
"default_call_policies.html#default_call_policies-spec">default_call_policies</a>.
If <code>T</code><i><small>n</small></i> is <a href=
"#optional-spec"><code>optional</code></a><code><U1, U2,</code>...
<code>U</code><small><i>m</i></small><code>></code>, the
expression's <em>valid prefixes</em> are given by:</dt>
<dd>
<blockquote>
(<code>T1, T2,</code>...<code>T</code><i><small>n-1</small></i>),
(<code>T1, T2,</code>...<code>T</code><i><small>n-1</small></i>
<code>, U1</code>),
(<code>T1, T2,</code>...<code>T</code><i><small>n-1</small></i>
<code>, U1, U2</code>),
...(<code>T1, T2,</code>...<code>T</code><i><small>n-1</small></i>
<code>, U1, U2,</code>...<code>U</code><i><small>m</small></i>).
</blockquote>
Otherwise, the expression has one <em>valid prefix</em> given by the
the template arguments the user specified.
</dd>
</dl>
<h4><a name="init-spec-observers"></a>Class template <code>init</code>
observer functions</h4>
<pre>
template <class Policies>
<em>unspecified</em> operator[](Policies const& policies) const
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> Policies is a model of <a href=
"CallPolicies.html">CallPolicies</a>.</dt>
<dt><b>Effects:</b> Returns a new <a href=
"#init-expressions"><em>init-expression</em></a> with all the same
properties as the <code>init</code> object except that its <em>call
policies</em> are replaced by a reference to
<code>policies</code>.</dt>
</dl>
<h3><a name="optional-spec"></a>Class template <code>optional<T1
=</code> <i>unspecified</i><code>, T2 =</code>
<i>unspecified</i><code>,</code>...<code>Tn</code> =
<i>unspecified</i><code>></code></h3>
<p>A <a href="../../../mpl/doc/refmanual/forward-sequence.html">MPL sequence</a> which
can be used to specify the optional arguments to an <code>__init__</code>
function.</p>
<h4><a name="optional-spec-synopsis"></a>Class template
<code>optional</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template <T1 = <i>unspecified</i>,...T<i>n</i> = <i>unspecified</i>>
struct optional {};
}}
</pre>
<h2><a name="examples"></a>Example(s)</h2>
<p>Given the C++ declarations:</p>
<pre>
class Y;
class X
{
public:
X(int x, Y* y) : m_y(y) {}
X(double);
private:
Y* m_y;
};
</pre>
A corresponding Boost.Python extension class can be created with:
<pre>
using namespace boost::python;
class_<X>("X", "This is X's docstring.",
init<int,char const*>(args("x","y"), "X.__init__'s docstring")[
with_custodian_and_ward<1,3>()]
)
.def(init<double>())
;
</pre>
<hr>
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=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
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