[C++-sig] Re: (no subject)

[David Abrahams]

Raoul Gough <RaoulGough at yahoo.co.uk> writes:

> Also, if you want to manage Python objects in C++, the Boost.Python
> library has some code to help with the reference count management,
> mostly in the "object" class. Maybe grepping for the (undocumented?)
> borrowed_reference or new_reference in the libs/python/src tree will
> provide suitable examples?

Uhm.  Those are really not for user consumption, which is why they're
not in namespace boost::python::.  I'm not sure it was the right
choice, but users are supposed to go through handle<> to acquire
references.  Either:

handle<> x(whatever);   // new reference
handle<> x(borrowed(whatever));  // borrowed reference

object(x); // now we have an object.


I've been thinking a bit about this interface recently.  I think
something like the following might be better:

     class reference 
     {
      public:
         PyObject* get() const;
         ...
      protected:
         reference(PyObject*);
         reference();
      private:
         void operator delete(void*); // not defined
         void operator delete(void*, size_t);
     };

     class borrowed_reference : reference
     {
      public:
         borrowed_reference(PyObject*);
     };
     
     class new_reference : reference
     {
      public:
         new_reference(PyObject*);
     };
     
This allows python::references to be passed around, but not
constructed.  You have to say borrowed_reference or new_reference
explicitly.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com