Re: [pygccxml-development] Recent Py++ modifications...

[Matthias B. <ba...@ir...>]

Roman Yakovenko wrote:
>> I've checked out Py++ from last week and gradually did updates to check
>> which one was responsible for the failure. The problematic modification
>> was done in revision 539:
>> http://svn.sourceforge.net/viewvc/pygccxml?view=rev&revision=539
>>
>> With this modification Py++ generates much more
>> implicitly_convertible<>() statements in the main function. For example,
>> I now have the following line which I think is responsible for the 
>> failure:
>>
>>      bp::implicitly_convertible< MFloatVector const &, MVector >();
>>
>> I can't say for sure what is going on inside of Boost.Python and why it
>> fails, but at least I know that everything has worked before this
>> modification.
>> What kind of problems was this modification supposed to fix?
> 
> I moved the logic whether to create "implicitly_convertible" code to
> decl_wrapper
> constructor class, where it should be.
> 
>> And how do
>> I get back to the previous behavior?
> 
> This test 
> http://svn.sourceforge.net/viewvc/pygccxml/pyplusplus_dev/unittests/casting_tester.py?view=markup&pathrev=539 
> 
> shows that it should work by default. Can you modify test case in a
> such way it will fail?

I created a small test file that demonstrates the problem. While doing 
so, I noticed that the problem only exists when I manually add the copy 
constructor to the bindings (which is what I'm doing for the Maya bindings).

Here's the C++ code:

struct Vector
{
   double val;

   Vector() : val(0) {}
   Vector(const Vector& v) : val(v.val) {}
   Vector(double x) : val(x) {}
};

struct FloatVector
{
   double val;

   FloatVector() : val(0) {}
   FloatVector(const FloatVector& v) : val(v.val) {}
   FloatVector(const Vector& v) : val(v.val) {}
   FloatVector(float x) : val(x) {}
};

Py++ doesn't wrap the copy constructor, so I do that manually for the 
FloatVector class:

root.Class("FloatVector").cdef("bp::init< const FloatVector& >()")

This adds the line

   bp::init< const FloatVector& >()

to the registration code of the FloatVector class.

The generated main function looks like this:

BOOST_PYTHON_MODULE(testlib){
     register_FloatVector_class();

     bp::implicitly_convertible< Vector const &, FloatVector >();

     bp::implicitly_convertible< float, FloatVector >();

     register_Vector_class();

     bp::implicitly_convertible< double, Vector >();
}


After compilation I try to create a FloatVector instance like this:

   fv = FloatVector(5.0)

The result of this is the following exception:

TypeError: No registered converter was able to extract a C++ reference 
to type Vector from this Python object of type float

When I remove the line

   bp::implicitly_convertible< Vector const &, FloatVector >();

then the above instantiation works.

- Matthias -