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Merged revisions 48987,49230-49231 via svnmerge from https://svn.boost.org/svn/boost/trunk ........ r48987 | danieljames | 2008-09-28 13:21:39 +0100 (Sun, 28 Sep 2008) | 1 line Clean up some link errors. ........ r49230 | danieljames | 2008-10-09 23:13:48 +0100 (Thu, 09 Oct 2008) | 1 line position_iterator is meant to be a forward iterator, so avoid using operator+ with it. ........ r49231 | danieljames | 2008-10-09 23:14:14 +0100 (Thu, 09 Oct 2008) | 4 lines Work around the problems with window newlines in position_iterator. (I'm about to fix them, but this will get quickbook working immediately). Fixes #2155 ........ [SVN r49242]
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6.5 KiB
HTML
166 lines
6.5 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
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<!-- Software License, Version 1.0. (See accompanying -->
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<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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<html>
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<head>
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<meta name="generator" content=
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"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link rel="stylesheet" type="text/css" href="../../../../boost.css">
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<title>Boost.Python - CallPolicies Concept</title>
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</head>
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<body link="#0000ff" vlink="#800080">
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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"header">
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<tr>
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<td valign="top" width="300">
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<h3><a href="../../../../index.htm"><img height="86" width="277"
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alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3>
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</td>
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<td valign="top">
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<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
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<h2 align="center">CallPolicies Concept</h2>
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</td>
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</tr>
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</table>
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<hr>
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<dl class="page-index">
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<dt><a href="#introduction">Introduction</a></dt>
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<dt><a href="#composition">CallPolicies Composition</a></dt>
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<dt><a href="#concept-requirements">Concept Requirements</a></dt>
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<dd>
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<dl class="page-index">
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<dt><a href="#CallPolicies-concept">CallPolicies Concept</a></dt>
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</dl>
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</dd>
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</dl>
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<h2><a name="introduction"></a>Introduction</h2>
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<p>Models of the CallPolicies concept are used to specialize the behavior
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of Python callable objects generated by Boost.Python to wrapped C++
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objects like function and member function pointers, providing three
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behaviors:</p>
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<ol>
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<li><code>precall</code> - Python argument tuple management before the
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wrapped object is invoked</li>
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<li><code>result_converter</code> - C++ return value handling</li>
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<li><code>postcall</code> - Python argument tuple and result management
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after the wrapped object is invoked</li>
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<li><code>extract_return_type</code> - metafunction for extracting the return type from a given signature type sequence</li>
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</ol>
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<h2><a name="composition"></a>CallPolicies Composition</h2>
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In order to allow the use of multiple models of CallPolicies in the same
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callable object, Boost.Python's CallPolicies class templates provide a
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chaining interface which allows them to be recursively composed. This
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interface takes the form of an optional template parameter,
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<code>Base</code> which defaults to <a href=
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"default_call_policies.html#default_call_policies-spec"><code>default_call_policies</code></a>.
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By convention, the <code>precall</code> function of the <code>Base</code>
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is invoked <i>after</i> the <code>precall</code> function supplied by the
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outer template, and the <code>postcall</code> function of the
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<code>Base</code> is invoked <i>before</i> the <code>postcall</code>
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function of the outer template. If a <code>result_converter</code> is
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supplied by the outer template, it <i>replaces</i> any
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<code>result_converter</code> supplied by the <code>Base</code>. For an
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example, see <a href=
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"return_internal_reference.html#return_internal_reference-spec"><code>return_internal_reference</code></a>.
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<h2><a name="concept-requirements"></a>Concept Requirements</h2>
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<h3><a name="CallPolicies-concept"></a>CallPolicies Concept</h3>
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<p>In the table below, <code><b>x</b></code> denotes an object whose type
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<code><b>P</b></code> is a model of CallPolicies, <code><b>a</b></code>
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denotes a <code>PyObject*</code> pointing to a Python argument tuple
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object, and <code><b>r</b></code> denotes a <code>PyObject*</code>
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referring to a "preliminary" result object.</p>
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<table summary="CallPolicies expressions" border="1" cellpadding="5">
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<tr>
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<td><b>Expression</b></td>
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<td><b>Type</b></td>
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<td><b>Result/Semantics</b></td>
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</tr>
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<tr>
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<td valign="top"><code>x.precall(a)</code></td>
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<td>convertible to <code>bool</code></td>
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<td>returns <code>false</code> and <code><a href=
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"http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>() != 0</code>
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upon failure, <code>true</code> otherwise.</td>
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</tr>
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<tr>
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<td valign="top"><code>P::result_converter</code></td>
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<td>A model of <a href=
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"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>.</td>
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<td>An MPL unary <a href=
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"../../../mpl/doc/refmanual/metafunction-class.html">Metafunction
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Class</a> used produce the "preliminary" result object.</td>
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</tr>
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<tr>
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<td valign="top"><code>x.postcall(a, r)</code></td>
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<td>convertible to <code>PyObject*</code></td>
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<td>0 <code>0</code> and <code><a href=
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"http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>() != 0</code>
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upon failure. Must "conserve references" even in the event of an
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exception. In other words, if <code>r</code> is not returned, its
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reference count must be decremented; if another existing object is
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returned, its reference count must be incremented.</td>
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</tr>
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<tr>
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<td valign="top"><code>P::extract_return_type</code></td>
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<td>A model of <a href=
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"../../../mpl/doc/refmanual/metafunction.html">Metafunction</a>.</td>
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<td>An MPL unary <a href=
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"../../../mpl/doc/refmanual/metafunction.html">Metafunction</a> used extract the return type from a given signature. By default it is derived from mpl::front.</td>
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</tr>
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</table>
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Models of CallPolicies are required to be <a href=
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"../../../utility/CopyConstructible.html">CopyConstructible</a>.
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<hr>
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<p>Revised
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<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
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13 November, 2002
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<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
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</p>
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<p><i>© Copyright <a href=
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"http://www.boost.org/people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
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<p>Permission to copy, use, modify, sell and distribute this software is
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granted provided this copyright notice appears in all copies. This
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software is provided "as is" without express or implied warranty, and
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with no claim as to its suitability for any purpose.</p>
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</body>
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</html>
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