1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Why is my automatic to-python conversion not being found?</title> 5<link rel="stylesheet" href="../boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Boost.Python"> 8<link rel="up" href="../faq.html" title="Chapter 5. Frequently Asked Questions (FAQs)"> 9<link rel="prev" href="how_can_i_automatically_convert_.html" title="How can I automatically convert my custom string type to and from a Python string?"> 10<link rel="next" href="is_boost_python_thread_aware_com.html" title="Is Boost.Python thread-aware/compatible with multiple interpreters?"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="" width="" height="" src="../images/boost.png"></td></tr></table> 14<hr> 15<div class="spirit-nav"> 16<a accesskey="p" href="how_can_i_automatically_convert_.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../faq.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="is_boost_python_thread_aware_com.html"><img src="../images/next.png" alt="Next"></a> 17</div> 18<div class="section"> 19<div class="titlepage"><div><div><h3 class="title"> 20<a name="faq.why_is_my_automatic_to_python_co"></a><a class="link" href="why_is_my_automatic_to_python_co.html" title="Why is my automatic to-python conversion not being found?">Why is my automatic 21 to-python conversion not being found?</a> 22</h3></div></div></div> 23<p> 24 <span class="emphasis"><em>Niall Douglas provides these notes:</em></span> 25 </p> 26<p> 27 If you define custom converters similar to the ones shown above the <code class="computeroutput"><span class="identifier">def_readonly</span><span class="special">()</span></code> 28 and <code class="computeroutput"><span class="identifier">def_readwrite</span><span class="special">()</span></code> 29 member functions provided by <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">python</span><span class="special">::</span><span class="identifier">class_</span></code> 30 for direct access to your member data will not work as expected. This is 31 because <code class="computeroutput"><span class="identifier">def_readonly</span><span class="special">(</span><span class="string">"bar"</span><span class="special">,&</span><span class="identifier">foo</span><span class="special">::</span><span class="identifier">bar</span><span class="special">)</span></code> is equivalent to: 32 </p> 33<pre class="programlisting"><span class="special">.</span><span class="identifier">add_property</span><span class="special">(</span><span class="string">"bar"</span><span class="special">,</span> <span class="identifier">make_getter</span><span class="special">(&</span><span class="identifier">foo</span><span class="special">::</span><span class="identifier">bar</span><span class="special">,</span> <span class="identifier">return_internal_reference</span><span class="special">()))</span> 34</pre> 35<p> 36 Similarly, <code class="computeroutput"><span class="identifier">def_readwrite</span><span class="special">(</span><span class="string">"bar"</span><span class="special">,&</span><span class="identifier">foo</span><span class="special">::</span><span class="identifier">bar</span><span class="special">)</span></code> 37 is equivalent to: 38 </p> 39<pre class="programlisting"><span class="special">.</span><span class="identifier">add_property</span><span class="special">(</span><span class="string">"bar"</span><span class="special">,</span> <span class="identifier">make_getter</span><span class="special">(&</span><span class="identifier">foo</span><span class="special">::</span><span class="identifier">bar</span><span class="special">,</span> <span class="identifier">return_internal_reference</span><span class="special">()),</span> 40 <span class="identifier">make_setter</span><span class="special">(&</span><span class="identifier">foo</span><span class="special">::</span><span class="identifier">bar</span><span class="special">,</span> <span class="identifier">return_internal_reference</span><span class="special">())</span> 41</pre> 42<p> 43 In order to define return value policies compatible with the custom conversions 44 replace <code class="computeroutput"><span class="identifier">def_readonly</span><span class="special">()</span></code> 45 and <code class="computeroutput"><span class="identifier">def_readwrite</span><span class="special">()</span></code> 46 by <code class="computeroutput"><span class="identifier">add_property</span><span class="special">()</span></code>. 47 E.g.: 48 </p> 49<pre class="programlisting"><span class="special">.</span><span class="identifier">add_property</span><span class="special">(</span><span class="string">"bar"</span><span class="special">,</span> <span class="identifier">make_getter</span><span class="special">(&</span><span class="identifier">foo</span><span class="special">::</span><span class="identifier">bar</span><span class="special">,</span> <span class="identifier">return_value_policy</span><span class="special"><</span><span class="identifier">return_by_value</span><span class="special">>()),</span> 50 <span class="identifier">make_setter</span><span class="special">(&</span><span class="identifier">foo</span><span class="special">::</span><span class="identifier">bar</span><span class="special">,</span> <span class="identifier">return_value_policy</span><span class="special"><</span><span class="identifier">return_by_value</span><span class="special">>()))</span> 51</pre> 52</div> 53<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 54<td align="left"></td> 55<td align="right"><div class="copyright-footer">Copyright © 2002-2015 David 56 Abrahams, Stefan Seefeld<p> 57 Distributed under the Boost Software License, Version 1.0. (See accompanying 58 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 59 </p> 60</div></td> 61</tr></table> 62<hr> 63<div class="spirit-nav"> 64<a accesskey="p" href="how_can_i_automatically_convert_.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../faq.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="is_boost_python_thread_aware_com.html"><img src="../images/next.png" alt="Next"></a> 65</div> 66</body> 67</html> 68
