[C++-sig] Providing a default value for a pointer argument

[Matthias Baas]

Hi,

I have a question about the "arg" class which can be used to provide 
names for keyword arguments and their default values. Should this 
default value also be taken into account for arguments that are actually 
pointers?
I have a function that takes a pointer as input whose default value in C 
is 0. When I wrap that function I provide the default value as 
arg("...")=0. I get no error when compiling such a module but the 
default value seems to be ignored and I must specify an argument 
explicitly (whereas I would have expected the default value to be None).
So is this a bug or just normal behavior? Below is a sample module that 
shows the problem. In this example it should be possible to call 
ptrarg() without any arguments, but when I do this I get the following 
error:

Boost.Python.ArgumentError: Python argument types in
     mod.ptrarg()
did not match C++ signature:
     ptrarg(class Spam * s=0)

Well, I do know how I can rewrite the module so that it does what I want 
(using thin wrappers, BOOST_PYTHON_FUNCTION_OVERLOADS, etc), I just 
thought I ask anyway because using "arg" would be rather convenient and 
maybe this is a bug in Boost.Python (as it also doesn't generate an 
error)...

- Matthias -


// Sample program:

#include <boost/python.hpp>

using namespace boost::python;

class Spam
{
};

int ptrarg(Spam* s=0)
{
   if (s==0)
     return 0;
   else
     return 1;
}

BOOST_PYTHON_MODULE(mod)
{
   class_<Spam>("Spam", init<>());

   def("ptrarg", ptrarg, (arg("s")=0));
}