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1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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3<!-- Copyright David Abrahams 2006. Distributed under the Boost -->
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13    <title>Boost.Python - &lt;boost/python/make_function.hpp&gt;</title>
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17    <table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
18    "header">
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26          <h1 align="center"><a href="../index.html">Boost.Python</a></h1>
27
28          <h2 align="center">Header
29          &lt;boost/python/make_function.hpp&gt;</h2>
30        </td>
31      </tr>
32    </table>
33    <hr>
34
35    <h2>Contents</h2>
36
37    <dl class="page-index">
38      <dt><a href="#introduction">Introduction</a></dt>
39
40      <dt><a href="#functions">Functions</a></dt>
41
42      <dd>
43        <dl class="page-index">
44          <dt><a href="#make_function-spec">make_function</a></dt>
45
46          <dt><a href="#make_constructor-spec">make_constructor</a></dt>
47        </dl>
48      </dd>
49
50      <dt><a href="#examples">Example</a></dt>
51    </dl>
52    <hr>
53
54    <h2><a name="introduction"></a>Introduction</h2>
55
56    <p><code><a href="#make_function-spec">make_function</a>()</code> and
57    <code><a href="#make_constructor-spec">make_constructor</a>()</code> are
58    the functions used internally by <code><a href=
59    "def.html#def-spec">def</a>()</code> and <code>class_&lt;&gt;::<a href=
60    "class.html#class_-spec-modifiers">def</a>()</code> to produce Python
61    callable objects which wrap C++ functions and member functions.</p>
62
63    <h2><a name="functions"></a>Functions</h2>
64<pre>
65<a name="make_function-spec">template &lt;class F&gt;</a>
66<a href="object.html#object-spec">object</a> make_function(F f)
67
68template &lt;class F, class Policies&gt;
69<a href=
70"object.html#object-spec">object</a> make_function(F f, Policies const&amp; policies)
71
72template &lt;class F, class Policies, class KeywordsOrSignature&gt;
73<a href=
74"object.html#object-spec">object</a> make_function(F f, Policies const&amp; policies, KeywordsOrSignature const&amp; ks)
75
76template &lt;class F, class Policies, class Keywords, class Signature&gt;
77<a href=
78"object.html#object-spec">object</a> make_function(F f, Policies const&amp; policies, Keywords const&amp; kw, Signature const&amp; sig)
79</pre>
80
81    <dl class="function-semantics">
82      <dt><b>Requires:</b> <code>F</code> is a function pointer or member
83      function pointer type. If <code>policies</code> are supplied, it must
84      be a model of <a href="CallPolicies.html">CallPolicies</a>. If
85      <code>kewords</code> are supplied, it must be the result of a <a href=
86      "args.html#keyword-expression"><em>keyword-expression</em></a>
87      specifying no more arguments than the <a href=
88      "definitions.html#arity">arity</a> of <code>f</code>.</dt>
89
90      <dt><b>Effects:</b> Creates a Python callable object which, when called
91      from Python, converts its arguments to C++ and calls <code>f</code>. If
92      <code>F</code> is a pointer-to-member-function type, the target
93      object of the function call (<code>*this</code>) will be taken
94      from the first Python argument, and subsequent Python arguments
95      will be used as the arguments
96      to <code>f</code>. <ul>
97<li>        If <code>policies</code> are supplied, it
98      will be applied to the function as described <a href=
99      "CallPolicies.html">here</a>.
100<li>If <code>keywords</code> are
101      supplied, the keywords will be applied in order to the final
102      arguments of the resulting function. 
103<li>If <code>Signature</code>
104      is supplied, it should be an instance of an <a
105      href="../../../mpl/doc/refmanual/front-extensible-sequence.html">MPL front-extensible
106      sequence</a> representing the function's return type followed by
107      its argument types.  Pass a <code>Signature</code> when wrapping
108      function object types whose signatures can't be deduced, or when
109      you wish to override the types which will be passed to the
110      wrapped function.
111</ul></dt>
112
113      <dt><b>Returns:</b> An instance of <a href=
114      "object.html#object-spec">object</a> which holds the new Python
115      callable object.</dt>
116
117      <dt><b>Caveats:</b> An argument of pointer type may
118      be <code>0</code> if <code>None</code> is passed from Python.
119      An argument type which is a constant reference may refer to a
120      temporary which was created from the Python object for just the
121      duration of the call to the wrapped function, for example
122      a <code>std::vector</code> conjured up by the conversion process
123      from a Python list.  Use a non-<code>const</code> reference
124      argument when a persistent lvalue is required.
125    </dl>
126
127<pre>
128<a name=
129"make_constructor-spec"></a>template &lt;class T, class ArgList, class Generator&gt;
130<a href="object.html#object-spec">object</a> make_constructor();
131 
132template &lt;class ArgList, class Generator, class Policies&gt;
133<a href=
134"object.html#object-spec">object</a> make_constructor(Policies const&amp; policies)
135</pre>
136
137    <dl class="function-semantics">
138      <dt><b>Requires:</b> <code>T</code> is a class type.
139      <code>Policies</code> is a model of <a href=
140      "CallPolicies.html">CallPolicies</a>. <code>ArgList</code> is an <a
141      href="../../../mpl/doc/refmanual/forward-sequence.html">MPL sequence</a> of C++ argument
142      types (<i>A1,&nbsp;A2,...&nbsp;AN</i>) such that if
143      <code>a1,&nbsp;a2</code>...&nbsp;<code>aN</code> are objects of type
144      <i>A1,&nbsp;A2,...&nbsp;AN</i> respectively, the expression <code>new
145      Generator::apply&lt;T&gt;::type(a1,&nbsp;a2</code>...&nbsp;<code>aN</code>)
146      is valid. Generator is a model of <a href=
147      "HolderGenerator.html">HolderGenerator</a>.</dt>
148
149      <dt><b>Effects:</b> Creates a Python callable object which, when called
150      from Python, expects its first argument to be a Boost.Python extension
151      class object. It converts its remaining its arguments to C++ and passes
152      them to the constructor of a dynamically-allocated
153      <code>Generator::apply&lt;T&gt;::type</code> object, which is then
154      installed in the extension class object. In the second form, the
155      <code>policies</code> are applied to the arguments and result (<a href=
156      "http://www.python.org/doc/current/lib/bltin-null-object.html">None</a>)
157      of the Python callable object</dt>
158
159      <dt><b>Returns:</b> An instance of <a href=
160      "object.html#object-spec">object</a> which holds the new Python
161      callable object.</dt>
162    </dl>
163
164    <h2><a name="examples"></a>Example</h2>
165
166    <p>C++ function exposed below returns a callable object wrapping one of
167    two functions.</p>
168<pre>
169#include &lt;boost/python/make_function.hpp&gt;
170#include &lt;boost/python/module.hpp&gt;
171
172char const* foo() { return "foo"; }
173char const* bar() { return "bar"; }
174
175using namespace boost::python;
176object choose_function(bool selector)
177{
178    if (selector)
179        return boost::python::make_function(foo);
180    else
181        return boost::python::make_function(bar);
182}
183
184BOOST_PYTHON_MODULE(make_function_test)
185{
186    def("choose_function", choose_function);
187}
188</pre>
189    It can be used this way in Python:
190<pre>
191&gt;&gt;&gt; from make_function_test import *
192&gt;&gt;&gt; f = choose_function(1)
193&gt;&gt;&gt; g = choose_function(0)
194&gt;&gt;&gt; f()
195'foo'
196&gt;&gt;&gt; g()
197'bar'
198</pre>
199
200    <p>
201    <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
202  13 November, 2002
203  <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
204    </p>
205
206    <p><i>&copy; Copyright <a href=
207    "../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002.</i></p>
208  </body>
209</html>
210
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