| 1 | <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> |
|---|
| 2 | |
|---|
| 3 | <!-- Copyright David Abrahams 2006. Distributed under the Boost --> |
|---|
| 4 | <!-- Software License, Version 1.0. (See accompanying --> |
|---|
| 5 | <!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) --> |
|---|
| 6 | <html> |
|---|
| 7 | <head> |
|---|
| 8 | <meta name="generator" content= |
|---|
| 9 | "HTML Tidy for Windows (vers 1st August 2002), see www.w3.org"> |
|---|
| 10 | <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> |
|---|
| 11 | <link rel="stylesheet" type="text/css" href=../../../../boost.css> |
|---|
| 12 | |
|---|
| 13 | <title>Boost.Python - CallPolicies Concept</title> |
|---|
| 14 | </head> |
|---|
| 15 | |
|---|
| 16 | <body link="#0000ff" vlink="#800080"> |
|---|
| 17 | <table border="0" cellpadding="7" cellspacing="0" width="100%" summary= |
|---|
| 18 | "header"> |
|---|
| 19 | <tr> |
|---|
| 20 | <td valign="top" width="300"> |
|---|
| 21 | <h3><a href="../../../../index.htm"><img height="86" width="277" |
|---|
| 22 | alt="C++ Boost" src="../../../../boost.png" border="0"></a></h3> |
|---|
| 23 | </td> |
|---|
| 24 | |
|---|
| 25 | <td valign="top"> |
|---|
| 26 | <h1 align="center"><a href="../index.html">Boost.Python</a></h1> |
|---|
| 27 | |
|---|
| 28 | <h2 align="center">CallPolicies Concept</h2> |
|---|
| 29 | </td> |
|---|
| 30 | </tr> |
|---|
| 31 | </table> |
|---|
| 32 | <hr> |
|---|
| 33 | |
|---|
| 34 | <dl class="page-index"> |
|---|
| 35 | <dt><a href="#introduction">Introduction</a></dt> |
|---|
| 36 | |
|---|
| 37 | <dt><a href="#composition">CallPolicies Composition</a></dt> |
|---|
| 38 | |
|---|
| 39 | <dt><a href="#concept-requirements">Concept Requirements</a></dt> |
|---|
| 40 | |
|---|
| 41 | <dd> |
|---|
| 42 | <dl class="page-index"> |
|---|
| 43 | <dt><a href="#CallPolicies-concept">CallPolicies Concept</a></dt> |
|---|
| 44 | </dl> |
|---|
| 45 | </dd> |
|---|
| 46 | </dl> |
|---|
| 47 | |
|---|
| 48 | <h2><a name="introduction"></a>Introduction</h2> |
|---|
| 49 | |
|---|
| 50 | <p>Models of the CallPolicies concept are used to specialize the behavior |
|---|
| 51 | of Python callable objects generated by Boost.Python to wrapped C++ |
|---|
| 52 | objects like function and member function pointers, providing three |
|---|
| 53 | behaviors:</p> |
|---|
| 54 | |
|---|
| 55 | <ol> |
|---|
| 56 | <li><code>precall</code> - Python argument tuple management before the |
|---|
| 57 | wrapped object is invoked</li> |
|---|
| 58 | |
|---|
| 59 | <li><code>result_converter</code> - C++ return value handling</li> |
|---|
| 60 | |
|---|
| 61 | <li><code>postcall</code> - Python argument tuple and result management |
|---|
| 62 | after the wrapped object is invoked</li> |
|---|
| 63 | </ol> |
|---|
| 64 | |
|---|
| 65 | <h2><a name="composition"></a>CallPolicies Composition</h2> |
|---|
| 66 | In order to allow the use of multiple models of CallPolicies in the same |
|---|
| 67 | callable object, Boost.Python's CallPolicies class templates provide a |
|---|
| 68 | chaining interface which allows them to be recursively composed. This |
|---|
| 69 | interface takes the form of an optional template parameter, |
|---|
| 70 | <code>Base</code> which defaults to <a href= |
|---|
| 71 | "default_call_policies.html#default_call_policies-spec"><code>default_call_policies</code></a>. |
|---|
| 72 | By convention, the <code>precall</code> function of the <code>Base</code> |
|---|
| 73 | is invoked <i>after</i> the <code>precall</code> function supplied by the |
|---|
| 74 | outer template, and the <code>postcall</code> function of the |
|---|
| 75 | <code>Base</code> is invoked <i>before</i> the <code>postcall</code> |
|---|
| 76 | function of the outer template. If a <code>result_converter</code> is |
|---|
| 77 | supplied by the outer template, it <i>replaces</i> any |
|---|
| 78 | <code>result_converter</code> supplied by the <code>Base</code>. For an |
|---|
| 79 | example, see <a href= |
|---|
| 80 | "return_internal_reference.html#return_internal_reference-spec"><code>return_internal_reference</code></a>. |
|---|
| 81 | |
|---|
| 82 | |
|---|
| 83 | <h2><a name="concept-requirements"></a>Concept Requirements</h2> |
|---|
| 84 | |
|---|
| 85 | <h3><a name="CallPolicies-concept"></a>CallPolicies Concept</h3> |
|---|
| 86 | |
|---|
| 87 | <p>In the table below, <code><b>x</b></code> denotes an object whose type |
|---|
| 88 | <code><b>P</b></code> is a model of CallPolicies, <code><b>a</b></code> |
|---|
| 89 | denotes a <code>PyObject*</code> pointing to a Python argument tuple |
|---|
| 90 | object, and <code><b>r</b></code> denotes a <code>PyObject*</code> |
|---|
| 91 | referring to a "preliminary" result object.</p> |
|---|
| 92 | |
|---|
| 93 | <table summary="CallPolicies expressions" border="1" cellpadding="5"> |
|---|
| 94 | <tr> |
|---|
| 95 | <td><b>Expression</b></td> |
|---|
| 96 | |
|---|
| 97 | <td><b>Type</b></td> |
|---|
| 98 | |
|---|
| 99 | <td><b>Result/Semantics</b></td> |
|---|
| 100 | </tr> |
|---|
| 101 | |
|---|
| 102 | <tr> |
|---|
| 103 | <td valign="top"><code>x.precall(a)</code></td> |
|---|
| 104 | |
|---|
| 105 | <td>convertible to <code>bool</code></td> |
|---|
| 106 | |
|---|
| 107 | <td>returns <code>false</code> and <code><a href= |
|---|
| 108 | "http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>() != 0</code> |
|---|
| 109 | upon failure, <code>true</code> otherwise.</td> |
|---|
| 110 | </tr> |
|---|
| 111 | |
|---|
| 112 | <tr> |
|---|
| 113 | <td valign="top"><code>P::result_converter</code></td> |
|---|
| 114 | |
|---|
| 115 | <td>A model of <a href= |
|---|
| 116 | "ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>.</td> |
|---|
| 117 | |
|---|
| 118 | <td>An MPL unary <a href= |
|---|
| 119 | "../../../mpl/doc/refmanual/metafunction-class.html">Metafunction |
|---|
| 120 | Class</a> used produce the "preliminary" result object.</td> |
|---|
| 121 | </tr> |
|---|
| 122 | |
|---|
| 123 | <tr> |
|---|
| 124 | <td valign="top"><code>x.postcall(a, r)</code></td> |
|---|
| 125 | |
|---|
| 126 | <td>convertible to <code>PyObject*</code></td> |
|---|
| 127 | |
|---|
| 128 | <td>0 <code>0</code> and <code><a href= |
|---|
| 129 | "http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>() != 0</code> |
|---|
| 130 | upon failure. Must "conserve references" even in the event of an |
|---|
| 131 | exception. In other words, if <code>r</code> is not returned, its |
|---|
| 132 | reference count must be decremented; if another existing object is |
|---|
| 133 | returned, its reference count must be incremented.</td> |
|---|
| 134 | </tr> |
|---|
| 135 | </table> |
|---|
| 136 | Models of CallPolicies are required to be <a href= |
|---|
| 137 | "../../../utility/CopyConstructible.html">CopyConstructible</a>. |
|---|
| 138 | <hr> |
|---|
| 139 | |
|---|
| 140 | <p>Revised |
|---|
| 141 | <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan --> |
|---|
| 142 | 13 November, 2002 |
|---|
| 143 | <!--webbot bot="Timestamp" endspan i-checksum="39359" --> |
|---|
| 144 | </p> |
|---|
| 145 | |
|---|
| 146 | <p><i>© Copyright <a href= |
|---|
| 147 | "../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p> |
|---|
| 148 | |
|---|
| 149 | <p>Permission to copy, use, modify, sell and distribute this software is |
|---|
| 150 | granted provided this copyright notice appears in all copies. This |
|---|
| 151 | software is provided "as is" without express or implied warranty, and |
|---|
| 152 | with no claim as to its suitability for any purpose.</p> |
|---|
| 153 | </body> |
|---|
| 154 | </html> |
|---|
| 155 | |
|---|
