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POSWIG, boost shared pointers and inheritance
 

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    <p>I'm having trouble with SWIG, shared pointers, and inheritance.</p> <p>I am creating various c++ classes which inherit from one another, using Boost shared pointers to refer to them, and then wrapping these shared pointers with SWIG to create the python classes.</p> <p>My problem is the following:</p> <ul> <li>B is a subclass of A</li> <li>sA is a shared pointer to A</li> <li>sB is a shared pointer to B</li> <li><p>f(sA) is a function expecting a shared pointer to A</p></li> <li><p>If I pass sB to f() then an error is raised.</p></li> <li>This error only occurs at the python level.</li> <li>At the C++ level I can pass sB to f() without a problem.</li> </ul> <p>I have boost 1.40 and swig 1.3.40.</p> <p>Below are the contents of 5 files which will reproduce the problem with:</p> <pre><code>python setup.py build_ext --inplace python test.py </code></pre> <p><strong>swig_shared_ptr.h</strong></p> <pre><code>#ifndef INCLUDED_SWIG_SHARED_PTR_H #define INCLUDED_SWIG_SHARED_PTR_H #include &lt;boost/shared_ptr.hpp&gt; class Base {}; class Derived : public Base {}; typedef boost::shared_ptr&lt;Base&gt; base_sptr; typedef boost::shared_ptr&lt;Derived&gt; derived_sptr; void do_something (base_sptr bs); base_sptr make_base(); derived_sptr make_derived(); #endif </code></pre> <p><strong>swig_shared_ptr.cc</strong></p> <pre><code>#include &lt;iostream&gt; #include "swig_shared_ptr.h" void do_something (base_sptr bs) { std::cout &lt;&lt; "Doing something." &lt;&lt; std::endl; } base_sptr make_base() { return base_sptr(new Base ()); }; derived_sptr make_derived() { return derived_sptr(new Derived ()); }; </code></pre> <p><strong>swig_shared_ptr.i</strong></p> <pre><code>%module(docstring=" Example module showing problems I am having with SWIG, shared pointers and inheritance. ") swig_shared_ptr %{ #include "swig_shared_ptr.h" %} %include &lt;swig_shared_ptr.h&gt; %include &lt;boost_shared_ptr.i&gt; %template(base_sptr) boost::shared_ptr&lt;Base&gt;; %template(derived_sptr) boost::shared_ptr&lt;Derived&gt;; </code></pre> <p><strong>setup.py</strong></p> <pre><code>""" setup.py file for swig_shared_ptr """ from distutils.core import setup, Extension swig_shared_ptr_module = Extension('_swig_shared_ptr', include_dirs = ['/usr/include/boost'], sources=['swig_shared_ptr.i', 'swig_shared_ptr.cc'], ) setup (name = 'swig_shared_ptr', version = '0.1', author = "Ben", description = """Example showing problems I am having with SWIG, shared pointers and inheritance.""", ext_modules = [swig_shared_ptr_module], py_modules = ["swig_shared_ptr"], ) </code></pre> <p><strong>test.py</strong></p> <pre><code>import swig_shared_ptr as ssp bs = ssp.make_base() dr = ssp.make_derived() # Works fine. ssp.do_something(bs) # Fails with "TypeError: in method 'do_something', argument 1 of type 'base_sptr'" ssp.do_something(dr) </code></pre>
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