[C++-sig] Problems splitting up a library

[Pertti Kellomäki]

I am exposing a largish library using Py++ and Boost.Python, and I'm 
running into a bit of a problem when I try to expose it in manageable 
parts. I've tried to condense the problem below.

One module contains class NIT:

==================================================
class NIT : public IT {
public:
     static NIT& instance();
//...
}
==================================================

which is exposed by Py++ as follows:

==================================================
struct NIT_wrapper : TT::NIT, bp::wrapper< TT::NIT > {
//...
};

BOOST_PYTHON_MODULE(mach){
     bp::class_< NIT_wrapper,
                 bp::bases< TT::IT >,
                 boost::noncopyable >
     ( "NIT", bp::no_init )
         .def("instance"
             , (::TT::NIT & (*)(  ))
                  ( &::TT::NIT::instance )
             , bp::return_value_policy< bp::reference_existing_object 
 >() )
         .staticmethod( "instance" );
     //...
==================================================

In another module, there is a member function that uses NIT as a default 
value:

==================================================
class I {
public:
     I(const TT::IT& iT = TT::NIT::instance());
     //...
}
==================================================

This is exposed by Py++ as follows:

==================================================
BOOST_PYTHON_MODULE(program){
     bp::class_< TTAProgram::I,
                 boost::noncopyable >
          ( "I",
            bp::init< bp::optional< TT::IT const & > >
                 (( bp::arg("iT")
                     =TT::NIT::instance( ) )) )
     //...
==================================================

Importing the "mach" Python extension as

	import TCE.base.mach

succeeds, but

	import TCE.base.program

results in the error message

	Traceback (most recent call last):
	  File "<stdin>", line 1, in <module>
	TypeError: No to_python (by-value) converter found
	for C++ type: TTAMachine::NullInstructionTemplate

If I remove the default value from the signature, the problem 
disappears. Any ideas how to fix this?

Thanks in advance.
-- 
Pertti