RE: [boost] Python & smart pointers

From: Trevor Perrin (tperrin_at_[hidden])
Date: 2001-07-08 18:31:06

I included the variants; below (and attached, if that works) is my test
file.  Probably vc just sucks.  Since splicing the converters directly into
python_extension_class_converters works for me that's what I'm going to do.
Thanks for your help.

Error:
-----------------------
c:\boost\boost_1_22_0\boost\python\caller.hpp(1071) : error C2665:
'from_python' : none of the 61 overloads can convert parameter 2 from type
'struct boost::python::type<class boostold::shared_ptr<class hello> >'
        c:\boost\boost_1_22_0\boost\python\detail\functions.hpp(69) : see
reference to function template instantiation 'struct _object *__cdecl
boost::python::caller<void>::call(void (__cdecl *)(class
boostold::shared_ptr<class hello>),struct _objec
t *,struct _object *)' being compiled

Test case
-----------------------
#include <boost/python/class_builder.hpp>
namespace python = boost::python;

#include "boostold/smart_ptr.hpp"

//Below I attempt to define from_python() and to_python() converters for
boostold::shared_ptr
BOOST_PYTHON_BEGIN_CONVERSION_NAMESPACE

template <class T>
PyObject* to_python(boostold::shared_ptr<T> p)
{
    return
boost::python::python_extension_class_converters<T>::smart_ptr_to_python(p);
}

template <class T>
boostold::shared_ptr<T>& from_python(PyObject* p, boostold::shared_ptr<T>&)
    { return
boost::python::python_extension_class_converters<T>::smart_ptr_reference(p,
boost::python::type<boostold::shared_ptr<T> >()); }

template <class T>
const boostold::shared_ptr<T>& from_python(PyObject* p,
boostold::shared_ptr<T>)
    { return
boost::python::python_extension_class_converters<T>::smart_ptr_value(p,
boost::python::type<boostold::shared_ptr<T> >()); }

template <class T>
const boostold::shared_ptr<T>& from_python(PyObject* p, const
boostold::shared_ptr<T>&)
    { return
boost::python::python_extension_class_converters<T>::smart_ptr_value(p,
boost::python::type<boostold::shared_ptr<T> >()); }

BOOST_PYTHON_END_CONVERSION_NAMESPACE

class hello{};

void func(boostold::shared_ptr<hello>){}

BOOST_PYTHON_MODULE_INIT(testbp)
{
  try
  {
    python::module_builder this_module("testbp");
    python::class_builder<hello> hello_class(this_module, "hello");
                this_module.def(func, "func");
  }
  catch(...)
  {
    python::handle_exception(); // Deal with the exception for Python
  }
}

-----Original Message-----
From: David Abrahams [mailto:david.abrahams_at_[hidden]] 
Sent: Sunday, July 08, 2001 3:36 PM
To: boost_at_[hidden]
Subject: Re: [boost] Python & smart pointers

You probably didn't define enough variants. You need:

    friend boost::shared_ptr<T>& from_python(PyObject* p,
boost::python::type<boost::shared_ptr<T>&>)
        { return smart_ptr_reference(p,
boost::python::type<boost::shared_ptr<T> >()); }

    friend const boost::shared_ptr<T>& from_python(PyObject* p,
boost::python::type<boost::shared_ptr<T> >)
        { return smart_ptr_value(p, boost::python::type<boost::shared_ptr<T>
>()); }

    friend const boost::shared_ptr<T>& from_python(PyObject* p,
boost::python::type<const boost::shared_ptr<T>&>)
        { return smart_ptr_value(p, boost::python::type<boost::shared_ptr<T>
>()); }

The type inside boost::python::type<...> is the type of parameter you are
converting to, so unless the function you're wrapping takes a reference to a
boostold::shared_ptr, no variation on what you have below will work.

-Dave

----- Original Message -----
From: "Trevor Perrin" <tperrin_at_[hidden]>
To: <boost_at_[hidden]>
Sent: Sunday, July 08, 2001 4:04 PM
Subject: RE: [boost] Python & smart pointers

>
> Sorry, that mail was incomplete, I sent it by accident.  Anyways, I 
> tried the below and tweaking it in various ways (ie 
> wrapping/unwrapping the boostold::shared_ptr in boost::python::type<>) 
> to make from_python() work
in
> a similar stand-alone way to to_python() but couldn't; I'm using 
> vc6sp4;
is
> there a simple way to do this?  I kind of get the impression from 
> conversions.hpp I'm out of luck..
>
> Trevor
>
> -----Original Message-----
> From: Trevor Perrin [mailto:tperrin_at_[hidden]]
> Sent: Sunday, July 08, 2001 12:58 PM
> To: 'boost_at_[hidden]'
> Subject: RE: [boost] Python & smart pointers
>
>
>
> Thanks.  What about from_python()?  By analogy with 
> python_extension_class_converters I tried:
>
> template <class T>
> boostold::shared_ptr<T>& from_python(PyObject* p,
boostold::shared_ptr<T>&)
>

>   return
>
boost::python::python_extension_class_converters<T>::smart_ptr_reference(p,
> boost::python::type<boostold::shared_ptr<T> >());
> }
>
>
>
>
> -----Original Message-----
> From: David Abrahams [mailto:david.abrahams_at_[hidden]]
> Sent: Sunday, July 08, 2001 5:39 AM
> To: boost_at_[hidden]
> Subject: Re: [boost] Python & smart pointers
>
>
> The formula is simple: just use this technique: 
> BOOST_PYTHON_BEGIN_CONVERSION_NAMESPACE // this is a gcc 2.95.2 bug 
> workaround
>   template <class T>
>   PyObject* to_python(my_smart_ptr<T> p)
>   {
>       return 
> boost::python::python_extension_class_converters<T>::ptr_to_python(p);
>   }
> BOOST_PYTHON_END_CONVERSION_NAMESPACE
>
> -Dave
> ----- Original Message -----
> From: "Trevor Perrin" <tperrin_at_[hidden]>
> To: <boost_at_[hidden]>
> Sent: Saturday, July 07, 2001 11:22 PM
> Subject: [boost] Python & smart pointers
>
>
> >
> > An uninformed question by a Boost.Python newbie:
> >
> > I've previously created a modified boost::smart_ptr for myself, and 
> > moved
> it
> > into a 'boostold' namespace.  Now I'd like to use at least 
> > boostold::shared_ptr with Boost.Python.  As a first stab I 
> > duplicated the bottom 4 converter member functions in 
> > extension_class.hpp/python_extension_class_converters, which refer 
> > to 'boost::shared_ptr', and changed 'boost::shared_ptr' to 
> > 'boostold::shared_ptr'.
> >
> > Which seems to work (I'm using vc6sp4; also I don't care about 
> > cross-extension-module dependencies right now), but I'm wondering if
> there's
> > a cleaner way to insert these converters into boost.python than 
> > modifying its code.  I'm also quite confused by the shared_ptr 
> > converter code within conversions.hpp; what is "wrapped_pointer", 
> > for example?  Is the "MUST_SUPPORT_MSVC" code in the comments an 
> > idiom I should be using?
> >
> > Trevor
> >
> >
> > Info: http://www.boost.org  Unsubscribe:
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> >
>
>
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